Storm Forecast
Valid: Fri 18 Jul 2008 06:00 to Sat 19 Jul 2008 06:00 UTC
Issued: Thu 17 Jul 2008 13:08
Forecaster: TUSCHY

SYNOPSIS

The main steering mechanism is a cyclonic vortex east of Iceland. Embedded in a strong polar front jet, numerous upper troughs and smaller scale disturbances rotate around this feature, affecting most parts of NW / N and central Europe. At the surface multitudinous fronts can be analyzed although the most active one can be found over eastern Europe, running from extreme W - Russia all the way down to the northern Adriatic coast. The atmosphere stays warm and stable over the Mediterranean, getting very hot over Spain and Portugal.

DISCUSSION

... Western Russia ...

The past few days already showed how unstable the atmosphere can be east of the eastward moving cold front with readings locally above 2500 J/kg MLCAPE. Not much change is forecast for the following 24 hours as moist BL and steep mid - level lapse rates overlap. In addition to at least widespread 1000 - 1500 J/kg MLCAPE just east of the front, DLS in the order of 20 m/s and enhanced LL shear can be found there, too. Large hail, strong to isolated severe wind gusts and a few tornadoes are all possible.

... Central Italy, Croatia, Bosnia and Herzegovina and the N - Adriatic Sea ...

The main inhibiting factor in this event will be a quite warm atmosphere with weak lapse rates. As a weakening frontal boundary moves southwards during the day, better BL moisture ahead of this front should support MLCAPE values around 500 J/kg. DLS is between 15 - 20 m/s , so multicells / an isolated supercell will evolve with an isolated large hail and strong wind gust risk.

Another round of thunderstorms develops over the western Alpine region during the later afternoon and evening hours as main upper trough axis and thermal trough approaches from the WNW. Despite a slow BL recovery during the day, lacking surface moisture will be an inhibiting factor for more robust instability release. DLS is quite strong so a few strong to isolated severe thunderstorms can evolve with a marginal hail and strong wind gust risk. We have to monitor the area for an higher hail threat if BL can recover better than currently anticipated.

... The rest of Europe ...

As a consequence of low geopotential heights and moderately steepened mid - level lapse rates, there is an extensive area where thunderstorms can evolve in a weakly to moderately sheared environment with low - end to modest instability release. Scattered, mainly diurnal driven thunderstorms will evolve with a marginal hail and strong wind gust risk. There are indications that locally enhanced LL CAPE release and low LCLs could support a tornado report, but run to run inconsistency and overall weak signals prohibit any level areas.

There is a chance for a few organized storms between a 00Z - 06Z time - frame over NE Ireland and northern / central parts of UK as a strong upper trough crosses the area from the WNW. Very limited instability release precludes any higher probabilities at the moment.



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