Storm Forecast
Valid: Tue 18 May 2010 06:00 to Wed 19 May 2010 06:00 UTC
Issued: Mon 17 May 2010 22:46
Forecaster: KOROSEC

A level 1 was issued for Belarus, Baltic states and parts of western Russia mainly for large hail and lesser extent for excessive convective rainfall.

SYNOPSIS

A large scale upper low with moderately cooled mid-levels dominates over eastern Europe and the Balkans and remains mostly stationary during the forecast period. On the eastern flank of the northwards building ridge, another, rather small scale upper low moves southwards across Germany and reaches the Alps on Wednesday morning. At surface, a weak surface low with an attendant quasi-stationary front over parts of eastern Europe and western Russia serves as a focus for main convective activity.

DISCUSSION

... Belarus, Baltic states and parts of western Russia ...

With the main upper low vortex staying stationary today, a daytime driven convective activity is expected along the well defined surface frontal boundary again. Mixing ratios near 10-12 g/kg suggest that MLCAPE of around 1500 J/kg will result. It seems that the main jet streak along the northern flank of this upper low is only partly overlaping with the instability, as the most CAPE stays to its north. Given the almost uncapped environment, its expected that widespread coverage of showers and thunderstorms will be mostly around the surface front. Despite the only weak to moderate shear, it will still support organized storms as numerous multicells as well as isolated supercells. Some of them with a threat for marginally large hail as well as excessive convective rainfall given the weaker wind field where CAPE is maximized.

... southern Germany...

An afforementioned small scale vorticity maxima crosses Germany from NW towards the Alps. A rather cold mid-levels with steep lapse rates will result in moderate destabilization. Marginal instability of several hundreds J/kg is likely given the expected good daytime surface heating. Favorable ascent associated with DCVA will lead into storms intiation along the progressing trough axis by midday and will continue towards the evening hours. Instability overlaps with moderate 20-25m/s deep-layer shear and therefore mostly elevated storms could be quite well organized. A threat for marginally large hail will exist, but the currently expected low coverage and especially only marginal instability precludes a threat level 1. However, the situation will be closely monitored for a possible upgrade if conditions improve significantly.

The rest of low probability lightning areas in central Italy and western Balkans (Apennini and Dynaric mountain range) will only see isolated storms where some of them could support some hail, but with sub-severe threat.