Storm Forecast
Valid: Wed 11 May 2011 06:00 to Thu 12 May 2011 06:00 UTC
Issued: Tue 10 May 2011 22:49
Forecaster: PUCIK

No threat levels have been issued.

SYNOPSIS

One of the main macrosynoptic features of the day at mid levels of troposphere will be a large ridge stretching from Southwestern Europe ino central parts of the continent and then subsequently into Scandinavia. Especially the western fringes of the ridge are expected to weaken and retreat with the arrival of two short-wave troughs associated with a cyclonic vortex centered over Iceland. Another significant feature will be a cold-core cut-off low over Southeastern Europe, almost stagnant and forecast to influence the weather over the region for a few consequent days. Relatively weak flow without any strong jet-streams is forecast, especially within the above mentioned large-scale pressure systems. Closer to the surface, a very inconspicuous situation with relatively high pressures over most of Europe, except for Southeastern Europe and Northwestern Europe. One of the main features regarding the thunderstorm development will be a cold front, which is expected to slowly progress across Western Europe.

12 UTC soundings and surface measurements reveal that models, especially GFS have overestimated surface dew points as well as the degree of CAPE and this mostly for the region ahead of the aforementioned surface cold front. Taking this into the considerations and refering to GFS simulations with a grain of salt, severe threat will be very low over most of the abundant thunderstorm regions over Europe. Diurnally driven thunderstorms are forecast over Central France, Germany, Northern Spain, Northern Portugal and over much of Southeastern Europe, where the cold mid-levels steepen considerably the lapse rates below.


DISCUSSION

... Northern/Northeastern Germany ...

The only region worth of discussion should be under a relatively stronger flow at mid-levels compared to the other regions (DLS increasing 15 m/s across the western fringes of the unstable region). Moreover, the passage of the shallow short-wave trough at mid-levels and the upward motion ahead of the surface cold front might help to eliminate any CIN and initiate thunderstorms. The factor of instability is, however, rather questionable with GFS simulating instability values around 1000 J/kg with dew points over 16°C. Current readings of several °C and approximately 12°C over Western Europe ahead of the flow do not seem to support the simulation and the instability will likely be less, as e.g. shown by ECMWF model. Nevertheless, should the GFS instability values prove right, slight threat of marginally large hail from multicellular convection would exist. At the moment, uncertainity prevents the issuance of Level 1.