Automatic recognition of squall line – a way to longer validity of some extrapolation rainfall nowcasting?

Most of meteorological phenomena that have significant impact upon society and infrastructure – such as heavy precipitation, thunderstorms, lightning, hail, hurricanes and tornadoes are related to convection. Therefore their recognition and forecasting play major role in operational aspects of national weather services, especially in the regions where such phenomena constitute one of the major weather features. Notwithstanding convective phenomena typical for mid latitudes are not so spectacular like those appearing in tropical regions, they are still the most devastating and causing majority of material losses. Squall line, being an important convective system, quite often bringing severe weather phenomena, is worth to be recognised automatically in order to monitor and forecast strong precipitation and related effects. As it normally lives longer than simple non-organised convection the extrapolation nowcasting of accompanied rain should be valid for longer time. Many attempts were done to work out the method of forecasting different aspects of convection (Agee, Chen, Dowell, 1973). A lot of failures resulted from very short life time of isolated convective cell and difficulties with predicting of triggering processes. Therefore we decided to focus on more stable phenomena, having simultaneously wider range. Basically, convective phenomena can be associated with three major types of convection (Markowski, 2005b). The first type is ordinary convection. The term covers variety of deep moist convection that is single-celled and a lifetime of which is approximately 45 minutes. This type of convection usually occurs near or shortly after the time of maximum daytime heating and dissipates after sunset. It rather seldom produces hail or wind gusts that could be classified as severe. In case severe weather is produced, its character is short lived and marginal. In contrast to ordinary convection, multicellular convection consists of numerous updrafts. This kind of phenomena is very common in mid latitudes. Such convective system has a