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Chapter IX: Conceptual Models

This section contains Webcasts on various conceptual models. The presentations do not focus on a particular case, instead they treat a conceptual model in a general manner so that the acquired knowledge becomes applicable to any similar weather event. Satellite imagery is always the starting point for the identification of a conceptual model; additional data from NWP, weather stations and Radar complete the mental picture of a conceptual model.

For a better orientation, the available Webcasts have been grouped into the following subchapters:

Most of the Webcasts were held at the "Synoptic and Mesoscale Analysis of Satellite Images" courses organized by EUMeTrain. They complement the "Manual of Synoptic Satellite Meteorology".

About conceptual models in general


The Manual on Synoptic Satellite Meteorology (Webcast, 56 minutes), 2016

Getting a good, actual weather picture within short time is essential for a forecaster who has to react quickly and adequately on weather changings.

The huge amount of weather data which are available makes it almost impossible for a human being to handle. Thinking in conceptual models is the only way to deal with this problem.

Meteorological satellites opened a whole new field in the conceptual model thinking in operational meteorology. Now there was an opportunity to recognize weather systems by detecting cloud patterns and verify this first guesses with observations and numerical parameters.

Within 20 years of the project fifty-three different conceptual models were described in a manual: Sat Manu. Also for the southern hemisphere, we have already fifteen CM's described.

The Manual on Synoptic Satellite Meteorology (Webcast, 65 minutes), 2014

Getting a good, actual weather picture within short time is essential for a forecaster who has to react quickly and adequately on weather changing's.

The huge amount of weather data which are available makes it almost impossible for a human being to handle. Thinking in conceptual models is the only way to deal with this problem.

Meteorological satellites opened a whole new field in the conceptual model thinking in operational meteorology. Now there was an opportunity to recognize weather systems by detecting cloud patterns and verify this first guesses with observations and numerical parameters.

Within ten years, European project fifty different conceptual models are described in a manual: Sat Manu. Last year a new project has started to describe also conceptual models which are typical for the southern hemisphere. Already eight of these CM's are described yet.

Satmanu (Webcast, 56 minutes), 2012

Conceptual models are everywhere around us, even in our heads. Human brain as it is, can store lot of impressions but processing these informations can be a big problem. That is why we need conceptual models in everyday communication to know what do others even talking about. All the model data, satellite data, observations, radar data, etc. require good processing of one forecaster so he can cope with all this information - that is where conceptual model fits in. Very chaotic processes in the atmosphere are today reduced to a smaller number of conceptual models, for the aim of better understanding of whole atmosphere. In this one-hour presentation Ab Maas, is introducing manual of conceptual models called Manual of synoptic satellite meteorology (Satmanu). This project started in 1995 and until now there were more than 50 conceptual models described in it, still now maintenance and updating of new models is present. Some of the features and examples of conceptual models are brought in this lecture.

Conceptual Models (Webcast, 10 minutes), 2010

A ten-minute recorded PowerPoint including audio and explaining you on what conceptual models are and why we use them in many of the training resources of EUMeTrain. The PowerPoint also shows examples from Sat Manu and provides you the basis to go to satreponline.org and learn this technique in more details.

Cyclogenesis and occlusions


Cyclogenesis and Occlusion Cloud Bands I (Webcast, 75 minutes), 2016

Cyclogenesis and occlusion cloud bands are common meteorological phenomena which are tightly connected. While "cyclogenesis" is a process, describing the development of a low centre, which can last from few hours to several days, the occlusion cloud bands are the result of this cyclogenesis process. Occlusion cloud bands differ from cold and warm front bands because of their history as well as their physical status.

The two lectures start from the classical cyclogenesis (occlusion) processes which are related to the classical polar front theory and introduce then the conveyor belt view of these processes culminating in the warm and cold conveyor belt occlusion types.

The occlusion cloud band types are described and compared to cold and warm front types in their horizontal as well as vertical depiction.

Also special subtypes of occlusion processes like "instant occlusion" and "cold air development" are mentioned.

Cyclogenesis and Occlusion Cloud Bands II (Webcast, 79 minutes), 2016

In this second part of the Cyclogenesis and Occlusion Cloud Bands lecture, a special form of cyclogenesis is treated in detail: the "rapid cyclogenesis" which is connected with very severe and often catastrophic weather events.

All processes and weather systems are presented from the aspect of "Conceptual Model thinking"; that means the typical appearance in satellite images is connected to the physical background which is responsible for the cloud configurations; then these results are connected to relevant numerical parameters in horizontal and vertical presentation. And all of the presented CMs are connected to the typical connected weather events. This combination of different meteorological material is especially important in forecasting and nowcasting.

Cyclogenesis and Occlusion Cloud Bands I (Webcast, 60 minutes), 2014

Cyclogenesis and occlusion cloud bands are common meteorological phenomena which are tightly connected. While "cyclogenesis" is a process, describing the development of a low center, which can last from few hours to several days, are the occlusion cloud bands the result of this cyclogenesis process. Occlusion cloud bands differ from cold and warm front bands because of their history as well as their physical status.

The two lectures start from the classical cyclogenesis (occlusion) processes which are related to the classical polar front theory and introduce then the conveyor belt view of these processes culminating in the warm and cold conveyor belt occlusion types.

The occlusion cloud band types are described and compared to cold and warm front types in their horizontal as well as vertical depiction.

Also special subtypes of occlusion processes like "instant occlusion" and "cold air development" are mentioned.

In the second part a special form of cyclogenesis is treated in detail: the "rapid cyclogenesis" which is connected with very severe and often catastrophic weather events.

All processes and weather systems are presented from the aspect of "Conceptual Model thinking"; that means the typical appearance in satellite images is connected to the physical background which is responsible for the cloud configurations; then these results are connected to relevant numerical parameters in horizontal and vertical presentation. And all of the presented CMs are connected to the typical connected weather events. This combination of different meteorological material is especially important in forecasting and nowcasting.

Cyclogenesis and Occlusion Cloud Bands II (Webcast, 68 minutes), 2014

Cyclogenesis and occlusion cloud bands are common meteorological phenomena which are tightly connected. While "cyclogenesis" is a process, describing the development of a low centre, which can last from few hours to several days, are the occlusion cloud bands the result of this cyclogenesis process. Occlusion cloud bands differ from cold and warm front bands because of their history as well as their physical status.

The two lectures start from the classical cyclogenesis (occlusion) processes which are related to the classical polar front theory and introduce then the conveyor belt view of these processes culminating in the warm and cold conveyor belt occlusion types.

The occlusion cloud band types are described and compared to cold and warm front types in their horizontal as well as vertical depiction.

Also special subtypes of occlusion processes like "instant occlusion" and "cold air development" are mentioned.

In the second part a special form of cyclogenesis is treated in detail: the "rapid cyclogenesis" which is connected with very severe and often catastrophic weather events.

All processes and weather systems are presented from the aspect of "Conceptual Model thinking"; that means the typical appearance in satellite images is connected to the physical background which is responsible for the cloud configurations; then these results are connected to relevant numerical parameters in horizontal and vertical presentation. And all of the presented CMs are connected to the typical connected weather events. This combination of different meteorological material is especially important in forecasting and nowcasting.

Rapid Cyclogenesis (Webcast, 60 minutes), 2013

Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure systems that occur in the middle latitudes and are associated with fronts (cold front, warm front and occlusion) and horizontal gradients in temperature and dew point, known as baroclinic zones. Extratropical cyclones are the everyday phenomena which, along with anticyclones, drive the weather over much of the Earth, producing anything from cloudiness and mild showers to heavy gales and thunderstorms. Evolution of these depressions can be recognized in the developing of the cloud systems. These cloud developments are the footprints of physical processes in the upper air. In case of explosive deepening it is called rapid cyclogenesis. Satellite imagery, especially recognition of cloud patterns and water vapour structures, can be a great help for marine forecasters to find the area where these cyclogeneses occurs. The deepening of the depression, where you can expect the strongest wind speeds at sea surface and what will be the distribution of the precipitation are issues which will be covered during the lecture. In general, the lecture will give insight in physical processes which can explain the development and life-cycle of rapid cyclogenesis by using single channel satellite images and RGB-images in combination with NWP model fields.

Lee Cyclogenesis in the Mediterranean (Webcast, 30 minutes), 2012

The classification of cyclones and their tracks in the Mediterranean will be presented, with a special attention on the lee cyclones and their tracks when moving farther from the initiation area. Furthermore, the atmospheric ingredients at play during lee cyclone formation and development will be reviewed, such as the crucial role of the upper-level dynamical factors, but also the near-surface lee-side thermal or potential vorticity (PV) anomalies and surface fluxes, including their interactions with the orography and mutual non-linear synergies. In addition, the use of "PV thinking" will be demonstrated for easier conceptual understanding of the formation mechanisms. The results of numerical studies show that the intensity and track of lee cyclones are very sensitive to the details of the upper-level trough, such as its exact position relative to the mountain, the intensity and existence of sub-synoptic vorticity cores, which may result in reducing the predictability of lee cyclones in the Mediterranean area.

Cyclogenesis (Webcast, 50 minutes), 2012

Two conceptual models from Satmanu manual are introduced by Barbara Zeiner from ZAMG; Rapid Cyclogenesis and Instant Occlusion. These are two kinds of cyclogenesis, but not the classical forms of an occlusion. In normal or classical occlusion there would be a broken wave in a polar front, but in this case we have somewhat different situation. In short, Rapid Cyclogenesis describes a very fast and intensive development of an Occlusion cloud spiral from a low level cloud head. Upper air processes are driving factors in such a development. On the other hand, Front intensification by jet crossing is development of thicker and mostly more convective cloud within a frontal cloud band in the left exit region of a jet streak during frontal crossing. All these processes in this lecture are supported by satellite images and lot of schematics from Satmanu Manual.

Occlusions (Webcast, 75 minutes), 2012

This lecture is somehow extension of previous lecture in the satellite course, and is given by Dr. Veronika Zwatz-Meise. She is speaking about Occlusions. There are five features connected to them and these are; Back-Bent Occlusion, Cold Air Development, Instant Occlusion, Cold Conveyor Belt Type and a Warm Conveyor Belt Type of Occlusion. Presentation is constructed in a way that first there is an explanation of how do occlusion cloud bands look like in different satellite images. Question of processes that take place in the troposphere that lead to what we see in satellite images is also discussed. After that meteorological numerical parameters that describe the occlusion processes in a best way are observed (both on isobaric and isentropic surfaces). And at the end answer to a question "Which special developments at/with occlusion cloud bands take place during their life cycle?" are answered.

Fronts and frontal substructures


Mesoscale Precipitation Bands within Cyclones (Webcast, 50 Minutes), 2016

Precipitation within extratropical cyclones often organizes into mesoscale substructures known as precipitation bands. The purpose of this presentation is to better understand how precipitation organizes into bands. We will discuss about Shapiro-Keyser and the Norwegian models of cyclones, why do they form, the differences between them, also where in cyclones precipitation bands form, their structures and evolutions, what controls their locations and intensities, and techniques to diagnose precipitation bands. In the end we will discuss about occlusion bands and how do they actually form considering latest researches.

Frontal Structures (Webcast, 52 minutes), 2016

Fronts as described in the "Bergen school" by Vilhelm Bjerknes are early conceptual models. Parameters typical for the changing of air masses were named and used by forecasters to recognize transition zones (fronts) between air masses. Satellite information expressed how right Bjerknes was in his CM thinking, but this information showed also that fronts can have much more complicated structure and life cycle Bjerknes could imagine.

In SatManu there are 5 different types of cold- and 3 different types of warm fronts that are recognized and described.

In this lecture we concentrate on warm- and cold fronts and show how we can analyze them with help of CM thinking.

Frontal Structures (Webcast, 52 minutes), 2016

Fronts as described in the "Bergen school" by Vilhelm Bjerknes are early conceptual models. Parameters typical for the changing of air masses were named and used by forecasters to recognize transition zones (fronts) between air masses. For nearly a century the method from the Bergen school is applied in the majority of weather rooms all over the world. Satellite information expressed how right Bjerknes was in his CM thinking, but this information showed also that fronts can have a much more complicated structure and live cycle Bjerknes could imagine.

In SatManu eight different types of warm- and cold fronts were recognized and described.

In this lecture we concentrate on warm- and cold fronts and show how we can analyze them with help of CM thinking.

Frontal Substructures (Webcast, 61 minutes), 2016

When observing the development of frontal zones in satellite imagery, forecasters should always keep an eye on frontal sub-structures like upper waves, front intensifications or rapid cyclogenesis. It is important to look for frontal substructures, because they often show new developments. NWP models sometimes catch the situation, sometimes not. Especially for rapid or small scale developments, model performance may leave a lot to be desired.

Here we focus on comparison of model outputs and satellite data regarding frontal substructures. Because the data are easily compared and show great results, satellite images are a good tool for model output verification.

Mesoscale Precipitation Bands within Cyclones (Webcast, 53 Minutes), 2014

Precipitation within extratropical cyclones often organizes into mesoscale substructures known as precipitation bands. The purpose of this presentation is to better understand how precipitation organizes into bands. We will discuss where in cyclones such precipitation bands form, their structures and evolutions, what controls their locations and intensities, and techniques to diagnose precipitation bands.

Frontal Substructures (Webcast, 53 minutes), 2014

When observing the development of frontal zones in satellite imagery, forecasters should always keep an eye on frontal sub-structures like upper waves, front intensifications or newly developing systems. NWP models sometimes catch the situation, sometimes not. Especially for rapid or small scale developments, model performance may leave a lot to be desired.

In this presentation, the focus will be on comparison between model output and satellite data in relation to fontal sub-structures. Model output such as simulated satellite imagery is easily compared to the most recent satellite images and hence form a perfect tool for estimating the model performance.

Frontal Structures (Webcast, 60 minutes), 2012

A weather front is a boundary separating two masses of air of different temperatures and humidity, thus different densities. They are often connected to a significant phenomenon such as showers and thunderstorms, and more generally to instability of the atmosphere. This lecture is based on two frontal structure types - Cold and a Warm font. In Satmanu there are five types or conceptual models related to Cold front; Arctic Cold Front, Cold Front (divided into Ana and Kata types), Cold Front in Cold Advection, Cold Front in Warm Advection and a Split front. Among Warm Front features there are; Detached Warm Front, Warm Front Band and a Warm Front Shield. In Satrep manual there are five chapters on each of above mentioned features; Cloud Structure in Satellite Images, Meteorological Physical Background, Key Parameters, Typical Appearance in Vertical Cross Sections and Weather Events. Ab Maas, will try to introduce these chapters to you, dealing with above mentioned types of Cold and Warm fronts.

Frontal Substructures (Webcast, 60 minutes), 2012

This one-hour presentation on Frontal Structures, brought by Andreas Wirth from ZAMG, is following content of chapter called "Substructures in fronts and initial stages of cyclogenesis", from Satmanu manual. But not all features under this chapter will be discussed. Lecture starts with Front Decay and Front Intensification by Jet Crossing. These are two very similar conceptual models but they show the opposite effect. This is followed by Upper Wave and Wave. Presenter will show these two conceptual models together to see the differences or the common features between them. Finally, presentation finishes with Secondary Low Centres in Occlusion Cloud Bands, which is feature easy to detect and not very complicated conceptual model.

Sting Jets (Webcast, 30 minutes), 2012

The presentation will discuss the strong winds that are sometimes found in the southwest quadrant of a cyclone and which on occasion can cause damaging winds at the surface. A conceptual model will be presented showing how these winds are related to air streams in the cyclone. Evidence for a distinct airflow known as a 'sting jet' will be presented - this is a descending jet of air reaching the top of the boundary layer a little behind the cold front. Reference will be made to results from recent experimental field campaigns to study this phenomenon.

New Concepts in Cyclone and Frontal CM (Webcast, 60 minutes), 2012

This talk presents new conceptual models in cyclone structures and evolutions. How does the large-scale flow in which the cyclone is embedded determine the type of frontal evolution that occurs? What are new ideas in occluded cyclone structure and formation? How does the air flow through cyclones, and what can this tell us about the possibility for deep, moist convection and organized precipitation bands? Are bands on satellite imagery really the location of fronts at the surface? Should we expect that the temperature gradient and wind shift necessarily are collocated with all fronts? How are our conceptual models of fronts being revised through new research? This talk concludes with general principles for how forecasters can improve their skill through the use of conceptual models in operational forecasting.

Cold air conceptual models


Polar Lows, facts and forecasting (Webcast, 55 Minutes), 2018

Polar Lows can be seen as small Arctic hurricanes, and they have a severe impact on shipping and coastal communities in Scandinavia. They are most common in the Barents Sea and the Norwegian Sea, but are also known to occur in the central North Sea and surrounding coastal areas. Polar lows are the most intense type of wintery convection weather phenomenon in this area. Thus, a familiarity with Polar Lows will also increase our ability to forecast the more common snow shower events in the winter season. This talk will present some facts on Polar Lows, how they are forecasted, and give examples of interpretation of satellite imagery.

Comma Clouds - Mesoscale Features in cold Air (Webcast, 60 minutes), 2016

Commas are meso-scale structures developing within cold air, that can cause severe weather on the ground, often behind frontal cloud bands. They occur mainly during the cold season and are a common feature for Northern and Western Europe - nevertheless commas can also be found in the south. In this lecture life cycles and the appearance of commas in satellite imagery will be demonstrated. Different types of development exist - Within the cold air commas can grow out of EC starting as a small feature which is growing in to the typical meso-scale cloud spiral. On the other hand, commas can be found in connection with occlusion when they split off the cloud spiral and become a separate feature on their own. Typical weather events are storms and heavy precipitation (in form of showers and thunderstorms). Examples of real cases will be shown and they shall illustrate the typical synoptic situations.

Polar lows (Webcast, 51 minutes), 2016

Polar Lows are generally characterized by severe weather in form of strong winds, snow showers sometimes even hail, which sometimes results in loss of lives, especially on the sea. Sometimes these systems are also connected with the term Arctic Hurricane, which had been used for especially intense Polar lows. Compromising definition of Polar low is: small, but fairly intense low in northern maritime regions.

The polar lows are formed in cold air outbreaks, north of the polar front, mostly in the regions east of 0°E and south of 75°N. Favorable season for them is the cold part of the year. By size, they are smaller (200-600 km) than ordinary synoptic lows with life-span typically around 18 hours, and with very intense change of weather.

Why was it difficult to forecast polar lows and what are the improvements in that area since 2000? In my presentation I will also show you how we are forecasting Polar lows, which models we are using and of course satellite products.

Comma Clouds - Mesoscale Features in cold Air (Webcast, 35 minutes), 2014

Commas are meso-scale structures developing within cold air, often behind frontal cloud bands. They occur mainly during the cold season and are a common feature for Northern and Western Europe - nevertheless commas can also be found in the south. As commas can cause severe weather this conceptual model is of high interest for forecasters. In this lecture life cycles of commas will be demonstrated and how they appear in satellite imagery - seen by MSG and polar orbiting satellites. On the theoretical side the physics behind these developments will be explained. Different types of development exist - Within the cold air commas can grow out of EC starting as a small feature which is growing in to the typical meso-scale cloud spiral. On the other hand, commas can be found in connection with occlusion when they split off the cloud spiral and becoming a separated feature on their own. The most important numerical parameters in connection with commas and their synoptic surrounding will be discussed. Typical weather events are storms and heavy precipitation (in form of showers and thunderstorms). Examples of real cases will be shown and shall illustrate life cycle and typical synoptic situations.

Polar lows (Webcast, 44 minutes), 2014

Polar Lows are generally characterized by a severe weather in form of a strong winds, showers and occasionally heavy snow, which had sometimes resulted in loss of lives, especially on the sea area. Sometimes these systems are also connected with term Arctic Hurricane, which had been used for especially intense Polar lows. Compromising definition of Polar low is; small, but fairly intense low in maritime regions.

They are formed in cold air outbreaks, north of the polar front, mostly in the regions east of 0°E and south of 75°N. Favorable season for them is cold part of the year. By size, they are smaller than the ordinary synoptic lows (200-600 km) with the life-span typically around 18 hours, and with very intense change of weather.

In my presentation I will show you how we are forecasting Polar lows, which models we are using and of course satellite products.

Polar lows (Webcast, 52 minutes), 2013

Polar lows are small but fairly intense lows that develop during cold air episodes during the winter season in the marine Arctic. The lecture will address some of the basic formation processes, the climatology and traditional forecasting based on deterministic short-range models. Recently, Polar Lows are tracked using fine scale EPS based on the UM, and presently the Harmonie 2,5 km model. Results are represented as an estimate of probability for PL tracks, wind and precipitation.

Polar Lows (Webcast, 30 minutes), 2012

The forecasting of Polar Lows is one of the most challenging tasks in weather forecasting in the arctic. The lecture will give a demonstration of basic forecasting methodology at the Norwegian Meteorological Institute, and show some typical signatures of the polar low as seen from satellite IR/visible imagery, from ASCAT and from other observational data. A climatologic survey is also given by the presenter.

Polar Lows - Arctic Hurricane (Webcast, 50 minutes), 2012

Polar Lows are generally characterized by a severe weather in form of a strong winds, showers and occasionally heavy snow, which had sometimes resulted in loss of lives, especially on the sea area. Sometimes these systems are also connected with term Arctic Hurricane, which had been used for especially intense Polar lows. Compromising definition of Polar low is small, but fairly intense low in maritime regions. They are formed in cold air outbreaks, north of the polar front, mostly in the regions east of 0°E and south of 75°N. Favorable season for them is cold part of the year. By size, they are smaller than the ordinary synoptic lows (200-600 km) with the life-span typically around 18 hours, and with very intense change of weather. As it is said before, within these Polar lows very strong winds can occur (15-25 KT, max. 52 KT) so understanding of these systems is of a great safety (and other) importance. All these facts and very nice example of Polar lows are presented by Justyna Wodziczko, from Norwegian Meteorological Institute.

Convection


Convective Cloud Features in Typical Synoptic Situations (Webcast, 50 minutes), 2016

Convection can be found everywhere on the planet. However, in meteorological way of thinking in mid-latitudes there is convection in different airmasses and also at the boundary of these airmasses. Convection at the boundaries belongs to the sub-features of frontal systems and we won't deal with convection in the frontal systems.

In this lecture a few examples of unstable air Conceptual models will be shown, for instance: Cumulonimbi, Enhancement of convection by PV, Spanish Plume, etc. The typical environment is one part and the organization modes is the second part of the lecture.

Convective Cloud Features in typical synoptic Situations (Webcast, 52 minutes), 2014

Convection can be found everywhere on the planet. However, in meteorological way of thinking in mid-latitudes there is convection in different airmasses and also at the boundary of these airmasses. Convection at the boundaries belongs to the sub-features of frontal systems and this lecture won't deal with the convection in the frontal systems.

Fortunately, as forecasters we know a lot about warm and cold airmass and especially when we are using the so-called airmass-RGB.

In this lecture a few examples of the cold air will be treated. However, most time will spend about convection in the warm air. The typical environment is one part and the organization modes is the second part of the lecture.

Tropopause Folding and Convection (Webcast, 30 minutes), 2012

Forecasting convective storms is one of the most difficult forecast challenges. One feature that has been claimed to have a positive influence and a negative influence on convective storms are tropopause folds, layers of stratospheric air that have been intruded down into the troposphere. To determine the relationship between tropopause folds and convective storms, this talk presents first the main conceptual models for the evolution of the upper-level fronts and associated tropopause folding. "Potential vorticity thinking" represents the framework for this discussion, thus advocating once more the utility of "PV thinking" for operational forecasters, not only as means of understanding the atmospheric dynamics, but also as a useful tool in the forecast process. In the second part of the talk, we will try to disentangle the conflicting paradigms that tropopause folds both promote and suppress convection, by analyzing the influence of tropopause folds on the ingredients for deep, moist convection. At the end of the talk we present some tools that can be used by the operational forecasters to assess the influence of tropopause folds on convection.

Convection in Typical Synoptic Situation (Webcast, 50 minutes), 2012

This lecture is about conceptual models connected to strong convective processes. For easier detection and understanding of these clusters, Key parameters are introduced. Most of times there is (Equivalent) Thickness (e.g between 1000 and 500hPa) given along with Potential (Wet Bulb) Temperature at 850 hPa, and together they present parameters for detection of warm areas in Troposphere suitable for convective processes. Low Level Convergence is a key parameter used for detection of areas of high convergence, thus triggering convective areas. Of course, Instability indices are given to track the areas of unstable atmosphere also suitable for cloud development. Some of the physical background and examples of convective processes is shown it this lecture, with help of Satmanu module and satellite images. Also one of the convective cloud features known as a Spanish Plume is described, along with four main types of thunderstorms (Single call, Multicell cluster, Multicell line and Supercell). Presenter of this lecture is Frans Debie, from KNMI.

Fog and low clouds


Shallow Clouds and related Weather Phenomena (Webcast, 66 minutes), 2016

Satellite image interpretation of shallow clouds and related weather phenomena is a very important task for nowcasting because NWP-models and statistical methods exhibit still deficiencies in simulating these phenomena in a proper way. Especially over oceans but also over land observation networks are often too coarse meshed for nowcasting.

The theory and the most suitable satellite products will be explained first. In combination with other data (e.g., observations, radio soundings, radar products) examples will be discussed for the following application areas:

  1. Diagnosing shallow clouds in respect to water content and related weather, e.g., drizzle of different intensities;
  2. Identifying fog and low stratus and how to estimate the fog/stratus layer's thickness. The likelihood of dissolving and connected weather phenomena (e.g., freezing drizzle) will be covered, too.

Shallow Clouds and related Weather Phenomena (Webcast, 67 minutes), 2014

Satellite image interpretation of shallow clouds and related weather phenomena is a very important task for nowcasting because NWP-models and statistical methods exhibit still deficiencies in simulating these phenomena in a proper way. Especially over oceans but also over land observation networks are often too coarse meshed for nowcasting.

The theory and the most suitable satellite products will be explained first. In combination with other data (e.g., observations, radio soundings, radar products) examples will be discussed for the following application areas:

  1. Diagnosing shallow clouds in respect to water content and related weather, e.g., drizzle of different intensities;
  2. Identifying fog and low stratus and how to estimate the fog/stratus layer's thickness. The likelihood of dissolving and connected weather phenomena (e.g., freezing drizzle) will be covered, too.

Orographic clouds


Convergence lines over Sea and Lakes (Webcast, 45 minutes), 2012

The intention of this case study lecture is to demonstrate the effect of an intensifying, marine cloud street (originated in continuing cold air advection over warm seawater) as a result of divergence and convergence at low levels over coastal regions and narrow straits. Frictional convergence and high instability appear to be the most important aspects for intense line convection. Although the divergence at low altitudes was not always very clear depicted in this case the large-scale divergence patterns at higher levels, the extreme low temperatures and the left exit of the Polar Jet streak overhead appeared to have a major impact. As a result, the marine cloud streets changed into active lines of hail and snow showers over sea and especially over land with quite a number of thunderstorms at time of the maximum temperature. The use of satellite imagery, surface and upper air weather charts almost simultaneously is of great help in detection and very short term weather forecasting (nowcasting). In very cold air objective instability indices, like Boyden, appear to be very helpful in forecasting low topped winter storms.

Convergence lines over Sea and Lakes in Denmark and Sweden (Case Study, 30 minutes), 2007

This a new example of the Conceptual Model, Convergence Lines over Seas and Lakes, is about a cloudstreet, developing into a well pronounced convergence line over the Sont, the narrow strait between Denmark and the southwest coast of Sweden. The evolution downstream over the west part of the Baltic Sea into the northwest part of Poland is studied as well. Coastal Convergence Lines, the other CM about developing convective clouds in cold air advection over warmer seawater, has a great similarity to convergence lines over sea and lakes. - Cloud streets, developed over sea, may intensify over land at a much larger distance from the coastline into an active squall line with embedded TS. An example of this side effect is presented as well.