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Chapter VIII: Case studies by topics

This section contains case studies covering various synoptic situations that have a severe impact on people and/or infrastructure. These case studies are training material in the sense that they point the reader's attention to past critical weather situations and provide useful material on how to analyze the synoptic situation. In order to facilitate the orientation, the cases have been subdivided into the following categories in alphabetic order:

Atmospheric waves


Unusual von Karman Vortex Streets near Azores Islands (Case Study, 30 minutes), 2009

On 25th April 2009, a possible but unusual pattern called von Karman vortex developed to the lee of Pico island. Very common in Madeira or Canary Islands, this feature is not so common in the Azores Islands mainly due to their location in Atlantic Ocean. Note that MSG Infra-red 10.8 and visible 0.6 channels on usual 3km sub-satellite pixel resolution can depict the pattern reasonably well in comparison to NOAA 1km resolution.

Convection


Weather Events Connected with the Advection of Warm Tropical Air Mass into Mid-Latitudes (Webcast, 22 minutes), 2017

A case study including three examples of tropical air advection into mid-latitudes is presented by Barbara Wrona from Polish Met Service (IMGW). These protrusions of warm and moist air caused convection and severe convection over a big part of the country. Barbara is going to analyze the latter one from the synoptic point of view and will tell us about the warnings that have to be issued in these cases.

A Case Study of the Severe Storm from 11 July 2016 (Webcast, 37 minutes), 2017

Izolda Marcinoniene from Lithuanian Met Service presented us the case study about a severe storm that happened on 11 July 2016 in Lithuania. Tropical air mass usually reaches Baltic states in the summer time and because of it convection develops in the region, but this case deserves a special treatment due to the intensity of the convection that happened. A mesoscale convective system (MCS) developed during the day over Poland and later shifted to Lithuania and Belarus.

Pukkelpop Storm (Case Study, 90 minutes), 2012

On 18 August 2011 a severe thunderstorm system developed over Belgium. It initiated over France and then passed over Belgium, the Netherlands and Germany. The studied thunderstorm grew fast and was long-lived. It was extremely severe; particularly the downdraft was extremely strong. The most intense part of the windstorm hit the Pukkelpop festival organized close to the city of Hasselt. There were 60 thousand people at the festival, staying mainly at the camping site. The strong wind flattened tents, uprooted trees, brought down festival light towers and TV screens, and caused a stage to collapse. Five people were killed and 140 people injured in the storm, ten of them seriously. The aim of this case study is to describe the synoptic situation in which the windstorm was initiated and developed, and to describe its characteristics by means of satellite, radar and lightning data and numerical simulation.

Storms of the 15th August 2010 (Case Study, 180 minutes), 2012

The storms, which occurred on August 15th 2010 in parts of central and eastern Europe, were interesting from many aspects, some of which are described in this case study. Given the highly variable appearance and characteristics of these storms the need existed to further examine in detail and to use the case for testing of various convection-related algorithms.

This case initially attracted our attention because of the severe hailstorm in Prague in the early evening, which caused an estimated 180 million EUR damage to property in less than one hour. This alone would not be a reason for focusing on this case; the main reason was the appearance of this storm's cloud top. From the MSG satellite perspective, the storm could have easily been overlooked due to its relatively warm cloud top and small size, as seen in the Meteosat 8 IR10.8 BT image below.

MPEF Divergence (Case Study, 60 minutes), 2011

On September 12th 2010 a major PV anomaly, in the rear of a cold front, moved over France and hit Germany and Switzerland in the late evening and also Austria during the night. On the front side of this anomaly convective cells developed and brought some rain showers and thunderstorms. At first the ECMWF-model, especially the 00 UTC run from September 12th, was lacking performance shifted the PV maximum more westward. In this case study we analyse not only the synoptic situation, but also the model error. In the following we take a look at the MPEF (Meteosat Product Extraction Facility) Divergence product, how it works and whether it would have been helpful in this case as a nowcasting tool.

Severe Convective Outbreak (Case Study, 150 minutes), 2011

A severe convective outbreak with big hail and thunderstorms occurred over parts of western and central Europe on Monday, May 25th 2009. Overnight, a strong squall-line developed that produced gusts in excess of 35 m s-1 across Northern France, Belgium and the Netherlands uprooting trees and causing considerable damage to property. In addition, hail with diameter of 10 cm. was recorded.

High Impact Weather (Webcast, 30 minutes), 2011

The EUMETCAL High Impact Weather group addressed a series of convective events over Europe between 5 and 9 August 2010. This events affected many countries from southern areas - Mediterranean/Balkans - to northern areas - Baltic/Scandinavia. In the 30-minute presentation the group analyzed the events, combining the analysis of convection, namely by satellite, with the impacts perspective.

Extreme case of convection over Austria associated with severe windbursts and hail (Case Study, 30 minutes), 2009

The 23rd of July 2009 was marked by a fast transition of a cold front (about 80 km/h) from west to east which went along with severe thunderstorms and hail. The catastrophic event caused enormous agricultural damage and the Austrian farmer alliance reported that about 60 000 hectare arable lands were devastated. The destruction mostly caused by hail was estimated to sum up 15 million euro. On this account people insist on investigations to find out what exactly caused the event. Besides on the meteorological perspective there is always great interest in improving forecast methods and forecast tools. In principle the following report provides a detailed analysis of the weather event. Basically the high potential of prefrontal thunderstorms was known, although there were diverse estimations about its development. It was the change of the wind direction due to the interaction between the convergence line and the foehn that induced the following weather development. Contributing to the wiki case studies this report should lead to a better understanding of the atmospheric conditions that special day and introduce new now casting-products (GII and SAI).

Convective clouds merging over Huaihe River in China (Case Study, 30 minutes), 2008

The 22nd of July 2008 was marked by a motion of a vortex with several convective cells along a frontal cloud band. At the leading edge of a frontal cloud system, lots of thunderstorms reported on the ground stations, and heavy rain, strong wind and lighten were observed. All of this weather events with caused enormous agriculture damage and economical lost. As the movement of vortex, several convective cells emerged and became a larger MCC because of merging each other, then the MCC was merged with a north MCC and brought severe weather in cloud area. So in this case, two different merging were analyzed in this case, first is the merger of cells and the second is a MCC merging with another one.

Cold U/V Storm Case over Western Turkey (Case Study, 30 minutes), 2008

A severe thunderstorm occurred at 5th of November 2007 at Cameli town at the western part of Turkey. After the thunderstorms phone calls have been made by persons from the municipality of Cameli and with eye-witnesses. According to them, a small-scale tornado had been observed and three villages in the suburbs of Cameli have been affected.

Mesoscale Convective System over the Balearic Island of Mallorca (Case Study, 180 minutes), 2007

On 4th October 2007 at 1530 UTC, a large Mesoscale Convective System (Mesoscale Convective System), passed over the Balearic Island of Mallorca. Associated to the Mesoscale Convective System an F2 tornado was reported. The Mesoscale Convective System was accompanied by severe wind gusts that spread the damage in numerous areas of the island. The longevity of the Mesoscale Convective System was quite remarkable (approx. 12 hours!), and in some stages of its life cycle, it showed a fast movement, taking a very short time, less than 1 hour, to cross Mallorca island.

Large Amounts of Precipitation over the Iberian Peninsula (Case Study, 120 minutes), 2007

The meteorological background to this case is rather classical with a persistent cyclone over the Atlantic and a frontal system over the Iberian Peninsula. Especially in the upper layers of the atmosphere the cyclone over the Atlantic causes a continuous flow of warm humid air in the direction of Spain. In the lower layers in the beginning of the case a frontal zone is recognized over Central Spain.

Within this frontal zone already at the beginning convective cells are seen embedded. Occasionally the development of V-shape storms indicates how fierce the convection is at these areas. A final extra chapter on a F2 Tornado in Mallorca concludes this case study.

Severe Convection over Central Europe (Case Study, 180 minutes), 2007

The period from 21th to 23rd June 2007 was marked by high convective activity in Central Europe. The thunderstorms were associated with hail and heavy wind bursts that killed several people and caused enormous financial damage. This case study bases on the reports provided by the meteorological services of Austria, Croatia and the Czech Republic. Next to Radar Observations and Stability analyses, now casting products will be assessed. It should be further noted that the so called cold ring shape in satellite imageries can be a major index for severe convection.

Summer convection over Central Europe (Case Study, 120 minutes), 2006

The case study describes the development of severe convection over Germany on 27 July 2006, which took place in the forefront of a cold front and an upper air trough. With the troughs approach the potential unstable warm and moist air over Central Europe was lifted. Supported by solar isolation, single cells and multi cells as well as super cells developed over eastern France and Germany, finally forming a north-south oriented squall line. Heavy precipitation of up to 30 mm/h and gusts of up to Beaufort 10 were registered.

Severe Convection over Austria (Case Study, 60 minutes), 2006

This case study addresses the formation of convection over Central Europe on 19th June. During that day the former tropical depression Alberto moved from the British Isles towards Scandinavia. In the warm sector of the frontal system several large Mesoscale Convective Systems developed rapidly. The convection was characterized by an extremely unstable atmosphere and a thickness ridge. The onset of convection and also its dissolution were clearly connected to the diurnal cycle.

After sunset only some remnant CBs remained. The comprehensive analysis of this weather event includes numerical parameters, single satellite imageries as well as combined products such as RGBs. Moreover, nowcasting tools like the NWCSAF, Radar measurements as well as the INCA analysis were analyzed closely.

Series of convective development over Turkey (Case Study, 60 minutes), 2006

The case study describes s series of convective developments which took place in front of a cold front as well as within the transition of that cold front. On 25th May first convective development were noticed over Romania at the leading edge of the front. Within the next few hours the convective developments started ahead of the front and were induced by orography.

During the night the convection was linked to the further movement of the cold front. The explosive convective development over Turkey on 26th May is nicely depicted in the set of radar-image and satellite images.

Prefrontal Convergence (Case Study, 60 minutes), 2005

On July 30th 2005 a prefrontal convergence line formed at the leading edge of a cold front. The long convergence line stretched from Italy over Austria into Poland and the Baltic States. Based on satellite imagery a sequence of thunderstorms could be observed. Moreover, it should be noted that this form of prefrontal convergence is clearly linked to the diurnal cycle. As night sets in, most of the cells dissolve.

Since convection is a rather small scale phenomenon, it can be beneficial to address high resolution limited area models such as ALADIN-AUSTRIA. The comprehensive analysis of ALADIN-AUSTRIA revealed converging motions at 925 hPa and the divergence (e.g. outflow of air near the cloud top) at 700 hPa. In regard to the stability analysis the nowcasting tool GII (Global Instability Index) provided by EUMETSAT proved to be useful.

Severe Convection over Central and Eastern Europe (Case Study, 120 minutes), 2005

In the case study two types of convective development are observed and addressed. At the 30th of May a broad N-S oriented frontal zone is covering Western Europe. On the leading side of this front several convective cells emerge. A further index for frontal intensifications is the dry intrusion which can be detected in the WV imagery can be observed.

Apart from that several cells emerge in Greece and Turkey. The convective development in Greece and Turkey can be characterized as fair weather convection. In this case study it will be shown that both convective developments have similarities but also differences. Based on satellite imageries and derived numerical parameters these differences and similarities will be accentuated. However, both weather events were associated with hail and lead to major damages in agriculture.

Severe Convection over the Ukraine (Case Study, 60 minutes), 2004

This case study addresses the formation of a mesoscale convective systems over the Ukraine on 9th and 10th July 2004 associated with heavy rainfall and hail. Cloud top temperatures of up to -70 degrees Celsius were observed. Moreover, it should be noted that the Carpathian Mountains played a central role, since the mountain ridge triggered a set of cells.

In this study the development will be observed closely based on satellite imageries and the NWP-field. Since the vertical stratification is essential for the formation of convection, stability indices will be assessed as well.

Mesoscale Convective System in Northern Germany and Denmark (Case Study, 120 Minutes), 2004

The case from 09 June 2004 is an example of an unusual development of a super cell because it developed over the relative cool water of the North Sea and a second phase of intensifying occurred about 4 hours after sunrise over Northern Germany. Precipitation amounts up to 20 mm and gusts up to Beaufort 10 were registered.

An intense frontal zone extended from England to Eastern Europe. The Southern parts of the North Sea and Northern Germany were affected by its warmer edge. Near the passage of the super cell the radio soundings exhibited a strong vertical wind shear, potential instability between 1 and 5 km height and a tropopause at about 12 km with -64°C.

The warm front was super-imposed by warm air advection and positive vorticity advection at the right entrance of a jet streak. That induced the development of a warm front wave. Within the potential unstable air during the evening of the 8th June a super cell developed near Scotland and moved after a temporary decaying and splitting till the morning of the 9th June to Hamburg. The right cell reached its maximum intensity at around 07 UTC.

Hail Catastrophe - 4 July 2003 (Case Study, 120 minutes), 2003

This catastrophic case describes the development of a Mesoscale Convective System starting in the Mid-Adriatic Sea and moving towards Bosnia and Herzegovina and then further NE. Heavy precipitation and flash flooding occurred in some Dalmatian towns, with severe hail inland.

Hail Catastrophe - 13 May 2003 (Case Study, 120 minutes), 2003

This case study deals with convective cells over Austria in a pre-frontal unstable airmass causing exceptionally intensive hail and a tornado in Vienna which is a rare phenomenon in this region.

Strong convective activity in a pre-frontal Convergence Line over Northeastern Europe: 29 May 2000 (Case Study, 120 minutes), 2000

The purpose of this study is to investigate the circumstances which caused this particular pre-frontal convergence line to develop and to compare them with those typical for the conceptual model Non-Orographic Convergence Line.

Case study of a Mesoscale Convective System associated to a convergence line, 11 June 1998 (Case Study, 30 minutes), 1998

In this case study a Mesoscale Convective System associated to a convergence line is described. The zone of strong convective activity initially extends from Estonia to Russia. During the life cycle it propagates to the North and finally reaches Southern Finland and causes heavy precipitation.

Prefrontal convection over Western Europe and France: 24-25 August 1997 (Case Study, 120 minutes), 1997

This case study shows prefrontal convection over western Europe and France. Numerous CB clusters and a dominating MCS are described.

Cyclogenesis


Mediterranean tropical-like cyclones (Medicanes) (Webcast, 50 minutes), 2018

The Mediterranean tropical-like cyclones are intense sub-synoptic maritime lows with strong winds, axisymmetric warm-core structure and tropical cyclone features, such as a cloud-free eye and spiral deep convection. They are frequently referred to as medicanes (MEDIterranean hurriCANES) due to their resemblance to tropical cyclones. Despite their low frequency (of about 1.1-1.6 systems per year), medicanes constitute a serious natural hazard to life, property and the environment of the coastal regions of the Mediterranean basin and the Black Sea. Their accurate prediction is a challenge for the numerical weather prediction models. This presentation includes some past cases of medicanes, the description of their structure and characteristics, criteria that are used to define them, the development mechanisms, climatology, consequences and finally a detailed case study of medicane Qendresa (November 2014).

Genoa Cyclone with Mistral (Case Study, 120 minutes), 2005

In this case the development of cyclone started in the Genoa Bay triggered by the strong north upper level flow. At the beginning of cyclogenesis, the flow of the cold air was tunneled through the Garonne Valley between the Pyrenees and the Massif Central and through the Rhone Valley between the Massif Central and the Alps. What makes this case special is the fact that the cyclogenesis was linked to a very strong Mistral over West Mediterranean during the whole period.

Rapid Cyclogenesis over Central Europe (Case Study, 120 minutes), 2004

In November 2004 a rapid cyclogenesis took place over central Europe. The cold front crossed central Europe in NW direction and brought intense precipitation in these areas. Strong gusts in Germany were restricted to higher regions. The storm reached its maximum on 19 November in the Tatra Mountains (Slovakia, southern Poland) where winds were orographically strengthened. On the lee side of the High Tatra, Wind speeds reaching about 80 to 100 kt in gusts were measured which had major impact on the environment.

The case study follows the development of a rapid cyclogenesis event with its origin over the Atlantic Ocean. Over central Europe an advanced stage of the Rapid Cyclogenesis can be observed. The mature stage is reached over Eastern Europe, represented by the development into a huge cloud spiral moving over Russia.

Rapid Cyclogenesis over Iceland (Case Study, 120 minutes), 2004

In this study a development of a mid-latitude cyclone will be shown. The development takes place because of the interaction between an upper level PV anomaly and a tightening/sharpening baroclinic zone, which can be identified as a low-level PV anomaly. Mutual interaction takes place which eventually leads to a deep surface cyclone. What makes this case special is the fact that the surface cyclone does not show much displacement, especially during the deepening phase. This could be linked to the effect of the orography in Iceland and the fact that the upper level trough is quasi-stationary.

In this investigation the development of this system will be closely observed on the basis of satellite imageries and the NWP-field. Moreover, the results will be linked to two conceptual models, namely Rapid Cyclogenesis and Upper Level Low.

Cyclogenesis over Scandinavia and the Baltic states (Case Study, 120 minutes), 2004

A cyclogenesis is a rather complex process leading to an occlusion stage of a frontal system. There are at least two main theories: the classical occlusion process according to the polar front theory and the rapid cyclogenesis being a result of several processes where stratospheric and tropospheric features are acting together.

This case shows a very intensive development from a small-scale comma to a synoptic scale cloud spiral. What makes this case so special is the fact that the cloud configurations are deviating from the usual development process of an occlusion spiral. Moreover, the relevant NWP parameters demonstrate a situation with high potential for further developments.

Cyclogenesis in the Mediterranean (Case Study, 120 minutes), 2004

The Mediterranean Sea favours the development of weak low-pressure systems. In many cases the development begins in or near the Genoa Bay in the mid Mediterranean. Cyclones then move either towards south-east, along the southern coast of Italy and end up in the eastern Mediterranean, or towards north-east, into the Adriatic, where in many cases they get stronger or trigger secondary cyclogenesis. However, once the cyclones are formed, they often produce periods of rainy weather. In this case the development started in the Mid Mediterranean and the cyclone moved north-east, into the Adriatic and was linked to high precipitation and strong bora winds.

Delay in Rapid Cyclogenesis over the Atlantic through the Development of an Upper Level Low: 2-3 August 1997 (Case Study, 120 minutes), 1997

This case study shows a delay in rapid cyclogenesis over the Atlantic through the development of an upper level low. Analysis of cloud features for separation of two CMs acting together.

Floods


Managing extreme weather and floods in the UK - winter of 2013/14 (Webcast, 30 minutes), 2014

The Flood Forecasting Centre (FFC) is a successful working partnership between the Environment Agency and the Met Office. We bring together the sciences of hydrology and meteorology in a jointly staffed specialist centre.

The winter of 2013-14 was the wettest for 250 years across England and Wales, with a succession of storms bringing sustained flooding from all natural sources, coastal, fluvial, surface water and groundwater. The presentation will start with an overview of the meteorological conditions that led to the largest coastal surge down the East Coast of England since 1953. The hydrometeorological conditions and flooding through late December 2013 to March 2014 will then be considered, along with examples and mechanisms of communicating the high impact conditions to emergency responders and Central Government. This included two briefings directly to our Prime Minister. Meteorological drivers and the possible teleconnections behind the exceptional conditions will also be considered.

Floods in SE Europe (Webcast, 35 minutes), 2014

From the beginning, spring 2014 was very rainy in large parts of central and south-eastern Europe. The soil was already saturated with water in the beginning of May, when mid-May a huge cyclone, persisting over Bosnia and Herzegovina, Serbia and Croatia for 3 days, caused extreme precipitation. The amounts measured in Serbia and Bosnia and along Sava river in Croatia were in some areas larger than ever measured before. Catastrophic flooding left thousands of people homeless and the consequences will be visible for a long time.

Heavy rain and floods (Case Study, 60 minutes), 2012

Last days of summer 2010, Slovenia and Croatia were marked by heavy rainfall and floods. The precipitation amounts in some parts of Slovenia was exceeding all recorded rainfall amounts in the last 100 years causing immense property damage and even human casualties. In the western part of Slovenia locally more than 500 mm of rain fell in 48 hours. Huge part of Slovenian territory was flooded, which included also more than 8200 houses.

The amount of rain in Croatia was not so great. In Gorski Kotar region (mountain area in the western part of Croatia) and in Istria in three days 200 to 300 mm of rain was reported causing mostly flash floods. The main problem in Croatia was the water that was brought by Sava river from Alpine region. Because of the instantaneous unit hydrograph, the southern part of Zagreb was flooded for several days.

Even though the prognostic material was giving the clear sign of a probability of heavy rain and the warnings were issued several days in advance, the amount of precipitation was so big that the damage was not possible to avoid.

This case study explains the processes that led to severe flooding and specialty of this study is that it brings and introduces H-SAF as a tool for detail monitoring which is of great help to the meteorological and hydrological specialists during and after the event. In this case study products of H-SAF are explained and some samples are presented.

Flash Flood in Pula (Case Study, 60 minutes), 2011

The case study shows that the flash floods in Pula were the result of a convective system which developed in the convergence zone caused by a specific placing of two Mediterranean cyclones. Generally, the Mediterranean region is recognized as one of the most cyclogenetic regions in the world. Mediterranean cyclones are classified in 3 major types: Genoa cyclones, Adriatic cyclones and non-Genoa cyclones. Although it is rather rare, the major-type cyclones can exist simultaneously belonging to the theoretical category of twin or eyeglass cyclones. The most common twins are the simultaneous Genoa and Adriatic cyclones (Brzovic, 1999), therefore classified as the 4th type of Mediterranean cyclones. Depending of the season and general synoptic conditions, the paths of the cyclones in the Mediterranean basin are diverse. On their way through this complex geography, they can produce a range of extreme weather phenomena such as heavy orographic precipitation, thunderstorms, supercells and mesoscale convective systems.

Catastrophic Flash Flood on Madeira Island (Case Study, 30 minutes), 2010

In the coastal city of Funchal at 20 February 2010 an amount of 111.5 mm (05:10-11:10 UTC) occurred in a 6-hour period (with a 24h amount of 144.3 mm). Higher amounts were recorded in the mountainous weather station Pico do Areeiro, at 1510 meters, with a 6-hour peak of 272.1 mm (08:50-14:50UTC). This mountain area is right upstream of Funchal, therefore, the precipitation in the mountain simply flowed downslope along rivers that are usually small, summing up to an already high amount of water in lower altitudes. A precipitation time-lag between Funchal and Areeiro is clearly depicted in the temporal evolution of 10-minute precipitation. Note values in excess of 10 mm/10 minutes in Funchal and 15mm/10 minutes in Areeiro during the most intense time periods. The Portuguese met. service followed this extreme event issuing gradually higher levels of precipitation warnings since the day before: yellow warning at 19:27 UTC on 19th, orange warning at 08:53 UTC on the 20th and red warning one hour later, at 10:03 UTC.

Silent Heavy precipitation in Madeira Island mountain areas (Case Study, 30 minutes), 2009

On 1st October 2009 almost 60 mm of precipitation have fallen in 6 hours (16-22 UTC) on a mountain station in Madeira Island (Areeiro, with a height of 1510m), which fitted the orange warning criteria (40 to 60 mm in 6 hours) used at the time at the Portuguese Met. Service. In a 24-hour period (12UTC on 1/10/2009 to 12 UTC on 2/10/2009) a total amount of 101 mm was recorded at the same weather station. An old large-scale low-pressure system was located over the Azores, to which a clear convective activity was related. These convective events were taking place to the northwest of Madeira Island and no special signal could be detected in satellite imagery at a first look over the island. Therefore, this episode could be considered to be kind of silent for this mean of observation.

Flash Flood in Istanbul (Case Study, 30 minutes), 2009

Torrential rainfall during the second week of September caused floods in the Istanbul area in Turkey. As a result, there were 32 casualties. Below we have pictured some satellite images with NWP. Striking is the Upper Level Low found over Central Turkey. This results in the advection of moist, unstable airmass from the Black Sea and topographic uplift which result in numerous rounds of showers and thunderstorms in the region. The cold temperatures found in the upper layers of the cold core low and its contrast to the warm surface causes the CBs to grow extreme in the vertical and producing lots of rain. Moreover, a weak wind field results in the slow storm movements.

Abundant rainfall Iberian Peninsula (Case Study, 30 minutes), 2008

On 23 September 2008 an amazing amount 326 mm in three hours was recorded in Sueca in the Province of Valancia. The convective events leading up to this event are discussed in this small case study by Ramon Vazquez. The satellite images as well as the radar and data from the ground are presented and discussed.

Flash Floods in Slovenia (Case Study, 60 minutes), 2007

This case-study presents the analysis of catastrophic flash floods in Slovenia that occurred on 18 September 2007. The flooding caused five casualties and huge material damage, estimated to more than 150 million Euro.

NWP models forecasted precipitation amounts of up to 100 mm/24h. That was the reason that the forecaster issued a warning for the precipitation at a rate of more than 100 mm/day, but the real values were much higher.

Besides analyzing synoptic and mesoscale conditions, that caused the extreme amount of precipitation, the objective of this study is also to show how nowcasting material can help a forecaster to issue additional warnings.

The synoptic analysis shows that on the day of the catastrophic event the area of low pressure was situated over the Northern Europe. A cold front was approaching the Alps and over Slovenia a series of prefrontal convective developments took place. In many regions in Slovenia the precipitation values were extremely high (>100 mm/day) with the maximum precipitation of 304 mm/24h officially measured in Kneske Ravne.

A long heavy rain period in the Baltic States and Finland (Case Study, 60 minutes), 2005

This study concentrates on two areas at the opposite sides of the low pressure area in the period 9 to 11 August 2009. The objective is to provide a detailed insight into the mechanisms that govern the formation of convection within a cold front (Finland) as well as prolonged rain within an occluded front (Lithuania).

In Lithuania the event was characterized by extreme rainfall (locally more than 250 mm in 3 days), leading to floods and severe damage. The south-westerly gusts on the 10th August caused uprooting of trees and further economic loss in excel of 45 million Euro. In Finland the most remarkable events were those connected with the passing of the cold front in the evening of August 9, associated with the intensive precipitation and lightning.

Flood Catastrophe Central Europe: 06 - 13 August 2002 (Case Study, 120 minutes), 2002

In August 2002 two Mediterranean low pressure systems developed, taking a so-called 5b path. Such occurrences are rather unusual in summer as was the very rapid repetition rate of two events within about 8 days. The first event happened between 06 and 08 August, the second between 10 and 13 August.

Life cycle of an Upper Level Low over the Bay of Biscay and the Iberian Peninsula: 24-30 September 1997 (Case Study, 120 minutes), 1997

This case study shows the life cycle of an upper level low over the Bay of Biscay and the Iberian Peninsula. Associated convective activity causes heavy precipitation and flooding in Spain.

Flood Catastrophe Central Europe: 04 - 08 July 1997 (Case Study, 120 minutes), 1997

Flood catastrophe in Central and Eastern Europe due to an Upper Level Low. Convective precipitation and barrage effects lead to extraordinary precipitation events.

Fog and low clouds


Fog and Stratus Cloudiness (Case Study, 60 minutes), 2012

This case study presents an analysis of radiation in a fog event over the Pannonian Basin that took place from 18th to 20th November 2011. It is an example of the conceptual model of fog and stratus cloudiness. Special attention is dedicated to the analysis of vertical atmospheric profiles (temperature, humidity and wind) combined with satellite observation.

Dense Fog on the south coast of Finland (Case Study, 30 minutes), 2009

On 21st May 2009 a dense advection fog coming from the Gulf of Finland caused low visibilities across the region around Helsinki. The fog started to move inland from the Gulf around 1700 UTC and persisted until next morning on land areas while coastal water areas cleared during daytime.

These kind of fog situations typically occur in the Southern coast of Finland in April-May when the sea temperature is still cold and warm humid air is advected over the water from Central Europe or the Baltic area (and in the autumn months in reverse fashion as the water is still warm and land cold). This case study is focused on comparing how a global model (ECMWF) and a local model (AROME) performed in forecasting this situation.

Prolonged Fog Episode in the UK (Case Study, 60 minutes), 2006

This case study presents the synoptic analysis of an event that took place from the 18th to 23th December over the UK. During this period dense fog was covering many places in the UK causing extremely bad conditions for aviation. For a busy international airport like Heathrow the cancellation of hundreds of flights just at the peak travel season (a few days before Christmas) meant chaos and significant economic loss. Changes in travel plans affected at least tens of thousands of passengers.

Fog itself is a common event on the British Isles at this time of the year. However, the duration of the episode justifies a closer look at the event. In addition, the visibility within the fog was at times very low, and this heavily affected the air-traffic even at airports having the most advanced instrumentation for low-visibility flight operations.

This study concentrates only on the area in the southeastern UK, but basically similar synoptic conditions with reduced visibility at times prevailed also on the European continent during this episode. What makes this case study differ from many other case studies is the absence or small influence of atmospheric fronts or dynamic forcing (such as PVA or PV anomalies).

Forest fires


Catastrophic Forest Fires in Caramulo Mountains (Case Study, 120 minutes), 2013

From 20 August to 2 September 2013 the Caramulo Mountains in central Portugal experienced a series of three large and devastating forest fire events that caused a total burned area of about 9415.5 ha and 6 casualties. The Caramulo fires had overwhelming ecological, social and economic consequences that will be felt for several years. They were the result of a complex combination of variables from human factors to adverse meteorological and topographic conditions. This case study will address these variables of the Caramulo fires, which lead to environmental disaster.

Forest Fires in Portugal and Russia (Webcast, 30 minutes), 2010

Presentation by Nuno Moreira (IM) and Andreas Wirth (ZAMG) on the exceptional summer of 2010 when a large scale crest was covering the two countries. As a result of the exceptional high temperatures and extreme low dew-point temperature the conditions were very dry. This resulted in a wide amount of forest fires. Within the high pressure and the lack of a governing flow the smoke caused many problems to Moscow.

Fronts and frontal systems


Passage of intense cold front over Europe (Case Study, 120 minutes), 2008

From 29 February to 1 March 2008, partly heavy thunderstorms with severe gusts and hail caused damages at several regions in Middle Europe. During only 12 hours a cold front and a succeeding convective line crossed Germany.

The storm Emma was a typical example of line convection with downbursts during a southeast movement of a storm field over the North Sea. The average velocity of the convective line was 110 km/h, sometimes 150 km/h. Behind the cold front dry atmospheric air (equivalent to high Potential Vorticity (PV)) could be recognised in the Airmass RGB.

Based on satellite imageries and numerical parameters the development of this event can be observed.

Meteorological perspective of a Meteo Tsunami on Island Losinj in the Adriatic Sea (Case Study, 30 minutes), 2008

On 15 August 2008, at about 17 UTC, a sea wave flooded the harbor of Mali Losinj on the island Losinj in the northern Adriatic. The flood was about 50 to 80 cm high above the ground what, together with the height of the ground above mean sea level, gives the wave height (trough-to-crest) of more than 2 m. This study is aimed to show that the flooding was caused by a Meteo Tsunami.

Severe cold front over Iberian Peninsula with later intensification by Jet (Case Study, 30 minutes), 2008

In northwestern Portugal, a maximum of 41 mm in 6 hours was obtained in an automatic weather station (AWS) in a mountain area and a maximum of 20 mm in 1 hour in a coastal area, both reaching the orange warning lower threshold for meteoalarm (40mm in 6 hours and 20mm in 1 hour, respectively). The Portuguese meteorological service (IM) issued a yellow warning with 24 hours advance, and the orange warning has been issued 7 hours before the beginning of the period of heaviest precipitation.

Cold Front over Middle Europe (Case Study, 120 minutes), 2006

This case study follows a cold front propagating from the Atlantic towards eastern Europe at the leading side of a deepening upper level trough. Special attention is paid to two waves developing on the cold front. Both of them show similar phases of development, from the first appearance of a cloud bulge to the formation of a cloud spiral.

The whole process can be observed in several types of satellite images: IR, WV and Airmass RGB composite. In the IR images the formation of the both wave bulges, intensification of the frontal cloudiness and cloud spiral development can be followed. The WV images enable the detection of the jet and the intrusion of dry stratospheric air. In the Airmass RGB the different air mass types as well as the position of the jet stream can be detected.

Formation of a Squall Line over Germany (Case Study, 60 minutes), 2004

During the 18th August a frontal cloud pattern moved from Western France to Central Germany. From noon until the evening this cloud pattern transformed into a squall line due to cyclonic vorticity advection induced by a short-wave trough. From the afternoon to the evening a mesoscale low with negative surface pressure tendencies developed east of the squall line. In combination with the increasing temperature contrast between the front and rear of the squall line, the velocity of the wind reached 100 km/h. Gusts of up to Beaufort 9 (flat areas) and 11 (mountainous regions) and precipitation of about 30 mm over Eastern France and Western Germany were observed.

Wave development over Eastern Europe (Case Study, 120 Minutes), 2004

This case study addresses the development of two waves within a frontal system over Central and East Europe. Waves are substructures of a cold front which indicates the initial stage of (secondary) cyclogenesis.

For this investigation two different waves will be analyzed using single satellite images as well as combined channel products. Moreover, conceptual models which base on a certain selection of numerical parameters will be introduced. Based on the development of the two different wave systems, the quality of the background information (satellite imagery, NWP-field) can be assessed.

Front Intensification from Sweden to Bosnia (Case Study, 120 minutes), 2004

This case study presents an interesting case of frontal intensification caused by jet crossing. The intensification of the frontal cloudiness takes place when a jet streak approaches the frontal cloud band.

In the satellite images elongated cloud fibres often indicate the location of jet axis, whereas the intensification area is well recognizable through much brighter grey-shades within the frontal cloud band. The areas of intensification are usually characterized by more intensive precipitation, often in shower form, sometimes accompanied by lightning.

Case study of a dark stripe associated to a depression over the Atlantic. 27 October 2002 (Case Study, 120 minutes), 2002

This case study will concern a Dark Stripe visible in water vapour imagery behind a Cold Front. This Dark Stripe indicates the presence of descending dry air, which can be of stratospheric origin. The stripe develops along the cyclonic side of the white water vapour band. Typical places of appearance of Dark Stripes are the rear of Cold Fronts and Occlusions, and the forward sides of Warm Fronts.

Front Decay over Central and Northern Europe: 2-3 June 2000 (Case Study, 120 Minutes), 2000

Front Decay over Central and Northern Europe. The impact of CA and distinct sinking within a frontal cloud band is shown in detail.

Case study of low-pressure systems with associated cloud bands over Eastern, Northeastern and Southern Europe, 14 - 15 June 1998 (Case Study, 120 minutes), 1998

Typical summer time distributions of low-pressure systems with associated cloud bands over Eastern, Northeastern and Southern Europe (Black Sea Low). Development of frontal parameters and weather events relevant for Scandinavia are discussed in detail.

Frontal System across Europe with Wave Development, 12 - 13 November 1997 (Case Study, 120 minutes), 1997

A frontal system located over Europe shows a wave development over south and south-eastern Europe and a front intensification over Spain between 12 and 13 November 1997. Special interest is focused on convective developments within the prefrontal area and the thickness ridge over the Balkan.

Convergence Cloud band in front of a Cold Front over Central and Eastern Europe: 29 July 1997 (Case Study, 120 minutes), 1997

This case study shows numerous cloud bands from west to central and eastern Europe are described. Special attention is drawn to the convergence cloud band in front of a cold front over central and eastern Europe, containing pronounced convective cloud features.

Cold Front containing strong convective activity over Western Europe: 7 June 1997 (Case Study, 120 minutes), 1997

This case study shows a cold front containing strong convective activity over western Europe. The development and life cycle of the convective cloud features are examined in detail.

Pronounced frontal system over the Atlantic and western Europe: 19 February 1997 (Case Study, 120 minutes), 1997

This case study shows a huge frontal system over the Atlantic and western Europe. A rapid cyclogenesis is associated with this system but deviating from the initial CM.

Cold Front with a distinct Wave over France: 17 April 1996 (Case Study, 120 minutes), 1996

This case study shows a cold front with a distinct wave over France and a special investigation about a rapid cyclogenesis over the northern Atlantic.

Extended long frontal cloud band west of Europe: 9-10 April 1996 (Case Study, 120 minutes) 1996

This case study shows an extended long frontal cloud band west of Europe consisting of cold front in cold advection and cold front in warm advection is diagnosed. Frontal substructures and a succeeding rapid cyclogenesis over the Atlantic are analyzed.

Cold Front over Western Europe: 12 March 1996 (Case Study, 120 minutes) 1996

This case study shows a dominating cold front over Western Europe. Special attention is drawn to the substructures within the frontal cloud band associated with the jet streak: Front Intensification and Wave.

Pronounced frontal system over West and Central Europe, causing strong precipitation: 18-19 February 1996 (Case Study, 120 minutes), 1996

Pronounced frontal system over West and Central Europe, causing strong precipitation. All associated Conceptual Models and the development of a Back Bent Occlusion are addressed in detail.

Storms


West storm moving east south of Iceland, and a case where forecasts and observations seem contradictory (Webcast, 30 minutes), 2018

Case 1: Between April 2. and April 4. 2018, gale to storm force winds from the west propagated from Cape Farewell, the southernmost point of Greenland over 1000 nautical miles across the Atlantic towards and past the Faroes Islands with high waves. This type of eastward wind/wave field propagation south of Iceland happens few times a year with varying intensity. Case 2: A showcase of the westerly Greenland tip jet creating large waves – but looking at the forecasted winds and waves versus observations, they seem contradictory, making the forecaster think twice.

An Atlantic Storm observed by Jason-2 - Significant Wave Height Altimetry (Case Study, 60 minutes), 2014

This case study treats a storm over the Atlantic which started its development on 14 April 2012 and lasted until 17 April. The deepening depression and associated strong surface winds gave birth to high waves and sea swell affecting the northern Spanish coasts. The case study focuses on the wave height altimetry data provided by Jason-2. A comparison with ECMWF wave model (WAM) is undertaken.

The aim of the case study is to show the quality of Jason-2 data in comparison with model data and in situ measurements.

Cyclone Emma on 1 March 2008 (Webcast, 30 minutes), 2012

On 1 March 2008, the powerful late winter cyclone Emma caused widespread damage and claimed 14 lives in Central Europe. Embedded in the synoptic-scale storm field, deep convection along the cold front played a significant role in further enhancing the wind gusts. This presentation aims to unfurl an outstanding case of a rapid cyclogenesis, to match the events at the earth's surface with the storm structures seen in satellite and radar data, and finally to track down possible mechanisms which may have contributed to paving the way for one of the strongest downbursts ever documented worldwide.

Storm Xynthia (Webcast, 30 minutes), 2012

In this presentation Nuno Moreira talks about Xynthia, a storm that affected North Atlantic and Europe in the end of February 2010. He focuses on the cyclogenesis process, which fits the classification of a "bomb", and on the remote observations of the storm. This observation does not only cover MSG imagery, but also ASCAT wind data and derived mean sea level pressure estimates. The advantages and disadvantages of using ASCAT wind in nowcasting for this kind of storms is also discussed.

Rapid Cyclogenesis or Medicane (Webcast, 25 minutes), 2012

This case study took place in Mediterranean basin from 7th to 8th November 2011, with some interesting weather phenomena occurred there. It is show that the sequential cloudiness type bands were; not organized convective system in the first step, then Comma feature in the next step, deep convection and finally Occlusion. Because of confusing weather features connected to it, this weather phenomenon cannot be classified as Tropical cyclone nor the Rapid Cyclogenesis. The case is treated only by a synoptic point of view, using Meteosat 9 satellite images and ECMWF numerical fields from ePort web site and other graphical elaborations with Metview.

Winter Storm Klaus (Case Study, 30 minutes), 2009

23 -24 January 2009 Storm Klaus was reaching explosive development rates as high as 34 mb in 24 hours, and registered maximum surface wind gusts of the order of 200 km/h. Klaus cyclone, as a system with a clear surface pressure signal, approximately started on day 23 about 00 UTC, in the middle of the Atlantic, at position shown below, with a minimum MSLP value of 1000 mb, according to ECMWF / HIRLAM analysis. The track of the cyclone was purely zonal and its speed was markedly high, reaching values above 100 km/h. A minimum surface pressure of about 964 mb at cyclone center took place on day 24 at about 00 UTC, more or less maintained for several hours during the warm seclusion phase of the system.

Hurricanes over the Atlantic (Case Study, 120 minutes), 2005

The extra tropical transition (ETT) of Hurricanes over the Atlantic is something that happens about 5 times a year and can severely disrupt the weather forecast. In this CAL the important features of ETT are addressed and physical theories are presented. After each chapter several exercises allow you to test the theory.

Extra Tropical Transition (Case Study, 60 minutes), 2004

This study concentrates on the case of hurricane Alex as it progressed though transition zone and crossed the Atlantic as an extra tropical cyclone. Between 31 July and 6 August 2004 the hurricane reached the Outer Banks in North Carolina. At this stage his intensity was classified as category 1. Within the further movements the hurricane strengthened and reached category 3.

This study will introduce the concept of ETT and compare it to other conceptual models. Therefore, several indicators from the satellite imageries as well as the derived numerical parameters will be analyzed.

Storm Catastrophe 13 - 16 November 2001 (Case Study, 120 Minutes), 2001

From 10th to 16th of November 2001 a series of intensive storms moved over the Northern Atlantic and passed through Scandinavia and Finland to the east. A few of the storms were remnants of hurricanes but the one storm that caused extensive damage, at least to Finland, was of a smaller scale. It was named "Janika".

Storm Catastrophe Atlantic and Western Europe: 25 - 28 December 1999 (Case Study, 120 minutes), 1999

Christmas Storms over Western and Central Europe due to successive Rapid Cyclogenesis development.

Winter weather


Forecasting Extreme Weather Using Probabilistic Tools (Webcast, 37 minutes), 2017

Cold lows that bring significant amounts of snow are quite rare in Israel and if they do appear they usually affect the mountainous area of the central part of the country. One such event happened in December 2013 and brought a lot of problems in traffic, power supply and also took lives. Shay Frenkel from Israeli Met Service described the synoptic situation of the event and told us what other tools to use and how did the climatology of the area affect the prediction.

Black Ice Case in January 2017 (Webcast, 29 minutes), 2017

Forecasting winter weather is a challenging job for a forecaster because of snow, ice, freezing rain, fog, etc. In this presentation Lars Kirchhuebel is presenting how are the winter weather situations, especially black ice phenomena, forecasted and warned in Deutscher Wetterdienst and during this walkthrough he will present the black ice case of 7th of January 2017.

Winter 2013/14 in USA (Webcast, 25 minutes), 2014

The cool season months of 2014 (JFM) over the U.S. mainland can best be described as much colder than normal across portions of the Great Lakes, Northeast, and Midwest, and much drier and warmer than normal over the west coast, especially California. This talk offered a review of three aspects of the winter/early spring seasons. The first was a review of 12 UTC temperatures for every day in January across the continental U.S. and the relationship of some of the colder mornings with the longer-term record of January mornings back to 1979. The second event of note was the onset of exceptional drought in California. The third event, coming at the end of March, was a look at significant cyclogenesis off the U.S. eastern seaboard on March 25-26.

Cold Air Outbreak (Case Study, 120 minutes), 2011

A Cold Air Outbreak directed by a strong anticyclone near Greenland directed polar air towards Europe. With the still relative warm waters of the North Sea and the genesis of several small-scale disturbances over Scandinavia and Germany the ingredients were in place for many centimeters of snow in the UK, Netherlands and Germany.

The largest impacts the snow brought were experienced from 16 to 20 December. The largest railway station in the Netherlands (Utrecht CS) was closed on 17 December due to snowfall leaving thousands of passengers stranded. During the morning rush hour of 18 December there was a record breaking 671 kilometers of traffic jam. In England the snowfall had also lead to chaos when motorists were stuck on the A21 during the evening and night of 17 to 18 December. The next night five international EUROSTAR trains were stuck in the tunnel under the English Channel leaving 2.000 passengers trapped for 16 hours.

From a meteorological point of view this cold air outbreak is interesting as many parts of Europe were affected and that there were different conceptual models responsible which can be distinguished using satellite and numerical weather data. All of these are described in detail in this case study.

Cold front with strong gusty winds over southwestern Finland (Case Study, 120 minutes), 2011

A cold air outbreak took place in Finland on September 29, 2009. The most interesting part of this particular cold air outbreak was unexpectedly strong wind gusts. Operational models, except one, did not give a hint about strong wind gusts. The strongest observed gust was 30 m/s but fortunately no hazards or problems were reported from the sea areas around Finland. Newspapers reported some fallen trees and observations of roofs being blown off properties in southwest Finland. In this article, this particular event is evaluated and presented together with observational and operational model data.

Strong wind gusts also affected the standard measured 10-minute average wind speeds, so that the forecasted maximum was 12 m/s and the observed 20 m/s, which is close to official storm wind speed threshold in Finland. Operational forecaster on duty corrected forecasts quickly after observations showed higher than forecasted wind speeds.

Heavy snowfall Austria (Case Study, 60 minutes), 2010

Between 10 and 12 February 2010 a Mediterranean low caused extreme snowfall in Styria and Carinthia, the south of Austria. This case study describes the synoptic situation and the further weather development during that time period. The comparison of the expected with the actual precipitation should show the accuracy of the forecast. On the basis of this case, an overview of the difficulties of precipitation forecast, especially for snowfall, is given.

Heavy Snowfall in Central Europe (Case Study, 60 minutes), 2010

An upper level cold core low depresses due to heavy cold air advection backside of the trough over the Iberian Peninsula. Heavy Snowfall in the Mediterranean area and in the following days in Austria and East Europe was the result of an intense cyclogenesis over the relatively warm Mediterranean Sea.

In addition to the heavy snowfall a very strong Bora established in the east Adriatic coast due to the great temperature and pressure gradient over the Dinaric coastal mountain. As a result of the very strong wind even some infrastructure was damaged in this area.

Case Studies with snow in Croatia and Lithuania (Webcast, 60 minutes), 2010

Izolda Marcinoniene will present a case study. According to Lithuanian criteria for meteorological phenomena it was a local-scale catastrophic event that affected the city of Nida, located on Baltic coast. Based upon the physical parameters of the atmosphere and the satellite information obtained, the situation was typical for Comma cloud. The main features and reasons for development of this catastrophic heavy snow event will be presented using detailed information such as vertical cross-sections, tephigrams and various satellite images.

The second talk will be presented by Natasa Strelec Mahovic from the Croatian Meteorological Service (DHMZ). DHMZ will give a presentation on the forecast and analysis of heavy snowfall in Croatia in February 2009, when snow was recorded even on the remote islands in Southern Croatia!

Massive Snowfall over the Netherlands and Germany (Case Study, 120 minutes), 2005

The case study describes the merging process of a comma-like cloud feature with a cold front cloud band. The term instant occlusion is used because the mature stage of the development shows a cloud spiral similar to that of a normal occlusion. But the meteorological processes are totally different from an occlusion process where advection of cold air lifts warm air. The process took place in an area of cold air without a warm front being present.

The subsequent snowfall caused an outage of power plants leaving people without heating and electricity for several days.

Polar Low: 27-29 January 2004 (Case Study, 120 minutes), 2004

In this case a Polar Low affected North-western Europe between the 27th and 29th of January 2004. The Polar Low moved along the Norwegian coast then southwards in a northerly flow and turned over the North Sea in the direction of the German Bight. Eventually the Polar Low made landfall over the border between the northern parts of The Netherlands and Germany.

Avalanche Catastrophe in the Alpine Area: 05 - 25 February 1999 (Case Study, 120 minutes), 1999

Avalanche catastrophe in the Alpine Area. Extraordinary high amount of snowfall due to persisting barrage effect at the Alps.

Case study of various CMs over Eastern Europe and a WV Eye over the Mediterranean, 15 - 16 March 1998 (Case Study, 120 minutes), 1998

Case study of various CMs over Eastern Europe and a WV Eye over the Mediterranean. Chronologically changing behavior of CMs during a cold air outbreak in the Mediterranean is the focus of interest.

Arctic cold air outbreak over western Scandinavia and successive Rapid Cyclogenesis., 29 - 30 January 1998 (Case Study, 120 minutes), 1998

Arctic cold air outbreak over western Scandinavia and successive Rapid Cyclogenesis at the Lee side of the Scandinavian mountains. The further development and severe weather events are investigated under the light of frontal connected jet streaks.