Storm Forecast
Valid: Wed 02 May 2012 06:00 to Thu 03 May 2012 06:00 UTC
Issued: Wed 02 May 2012 06:14
Forecaster: PUCIK

A level 1 was issued for Germany mainly for excessive precipitation and large hail.

A level 1 was issued for Belgium and SE Netherlands mainly for excessive precipitation.

SYNOPSIS

The main macrosynoptic feature at mid-levels will be a cyclonic vortex over the Atlantic, with a trough stretching into Northern Italy in the beggining of the forecast period. Satellite images as of Tuesday 21 UTC reveal a well developed cyclonic vortex within this trough. Towards the east/southeast a n inconspicuous higher geopotential fields prevail. Going to the north a brisk mid-level flow with several disturbances covers Central to Northern Scandinavia. Closer to the surface, an unseasonably warm airmass is present over much of Central Europe. This airmass is characterised by rather steep lapse rates and relative dryness although dewpoints did increase slightly over the area during the recent few days. A diffuse frontal boundary is predicted over Germany and a sharp frontal zone running from Scandinavia to Russia.

DISCUSSION

... Central to Southeastern Europe ...

Numerical models are in general disagreement regarding the degree of instability and convective initiation for this region. Major obstacles regarding the certainity are the low level dew points and the position of mesoscale lifting mechanisms. Tuesday 12 UTC soundings reveal more unstable and moister conditions over W Poland, Germany and the Adriatics. As of Tuesday evening, several convective clusters were ongoing over Germany/Poland border, western half of Poland and Austria. As of early morning status, an MCS is ongoing over W Germany/France border and over Central Germany. Outflow boundaries laid out by these clusters might be the focus for thunderstorm initiation during this day. High LCLs and CAPE predominantly in hail growth zones point to the chances of marginally large hail within stronger cells despite weak wind shear limiting storm organisation. Nevertheless, questionable degree of instability and storm initiation prevent issuance of Lvl 1 for most of this area.

... Germany, Belgium, SE Netherlands ...

The best agreement between different NWP regarding the instability/initiation question should be this area with moderate instability release predicted by GFS, ECMWF, HIRLAM and numerous WRF runs. Instability could locally exceed 1000 J/kg with rather weak DLS, generally under 10 m/s. Moderate values should be observed in the western/southern part of Lvl 1 thanks to the vicinity to the approaching trough. Frontal zone along with the advancing trough from south should act as the lifting factors for this situation. Generally speaking, situation will favor unorganised convection, most likely in the form of multicell clusters. More organised convection, including some marginal supercells is more likely above W and SE Germany where DLS around 15 m/s and enhanced SREH ahead of the surface low is forecast. This notion is well supported by Stuttgart, Munich and Idar-Oberstein 00 UTC soundings. Moderate instability along with most of CAPE in the hail growth region could lead to marginally large hail in the stronger cells. Also, enhanced mixing ratios over the area with slow storm motions could cause locally excessive precipitation within thunderstorm clusters that manage to develop a training pattern of cell. A Lvl 1 is issued for this region due to the combination of these two threats. Threat for excessive precipitation should be the highest over western, while for hail mostly over central to southeastern part of the highlighted area.