Forecasting of the weather involves predicting conditions beyond the range of linear extrapolation of current conditions. For severe thunderstorms, this typically means from an hour or so ahead to a few days and covers spatial regions out to the order of thousands of kilometers. Nowcasting is restricted to shorter time and space scales, frequently focusing on short-term, local changes in the environments and in the behavior of individual thunderstorms.
Forecasting of severe thunderstorms begins with an understanding of the ingredients that the atmosphere requires for thunderstorms (lower tropospheric moisture, mid-tropospheric potential instability, and an initiation mechanism), and adds in the organizing effect of tropospheric wind shear. Although pattern recognition techniques can play a role in identifying situations in which those ingredients can come together, they are limited in their quantitative application.
Nowcasting uses a variety of tools and sensors to look at short-term changes in the atmosphere. Much of its information comes from qualitative sources (e.g., satellite imagery to detect boundary locations, radar images depicting an individual thunderstorm). Although successful nowcasting requires an understanding of the likely events of a particular day developed by forecasting, the short time scales involved add the additional requirement of rapid decision-making by the meteorologist.
Relationships between large-scale environmental conditions and the weather events that occur, assuming storms are initiated, have been developed over the years with the use of proximity sounding studies, particularly using data from the United States. Given the relatively modest values of instability in Europe compared to the United States, relationships focusing on typical European conditions are needed. A further point of interest comes from recent work that suggests that, given those conditions, storms are more likely to be initiated in Europe than with similar conditions in the US. The nature and forecasting of convective-initiating boundaries provide a wide array of research problems that need to be addressed to improve forecasting.
There are many challenges to nowcasting severe storms in Europe. The relative lack of experience in radar interpretation and in the development of algorithms to assist forecasters in making decisions limits what can be done. Beyond that, given that a primary goal of public sector forecasting is to provide information to protect life and property, the general low level of public awareness of severe thunderstorms makes communicating important messages difficult. It also frequently means that forecasters don?t receive information on events that could improve the next set of forecasts in a timely manner. Developing relationships and tools to communicate information into and out of the forecast process are areas that are ripe for research.
We invite submissions of contributions on all the above aspects.