Understand NWP outputs

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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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 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.

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South Africa is by nature a dry country, which has very short wet periods, mainly confined to the coastal areas and eastern half of the country. During the dry season, the hot, windy conditions result in a favourable environment for fires to spread uncontrollably and cause large scale damage to the local vegetation and to infrastructure. To be able to anticipate and forecast the risk of runaway fires in South Africa, a forecaster needs to have many sources of information, ranging from precipitation amounts to an understanding of the local vegetation. The inclusion of satellite imagery interpretation is an invaluable part of the forecasting process and the monitoring of fires can be done accurately and on a 24hour basis. This presentation will outline the risk the fires pose within South Africa and our forecasting processes dealing with this environmental hazard.

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Meteorologists and weather technicans from the German Meteorological Service (DWD) attended the entire MOSAiC expedition, the largest-scale Central Arctic research expedition of all time. They were responsible for permanent weather observations and daily meteorological forecasts for scientists, ship master and officers, as well as helicopter pilots. Our presentation will report about personal experiences of a meteorologist on board of the research icebreaker POLARSTERN, with the focus on the daily work of the forecaster and the importance of using satellite images in Polar Regions.

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Snowy winters lead to heavy snow loads on buildings and constructions. Surprisingly often, the snow load assessment basis of international and national standards are regionally reached or exceeded. Damages or even collapses do occur, cause expenses and threaten human lives. However, extreme snow loads only rarely are considered as natural hazards. This talk puts heavily burdened roofs in the spotlight by presenting recent efforts in updating the Austrian snow load standard and showing an actual example of snow load monitoring and hazard management.

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