Storm Forecast
Valid: Sun 01 Jun 2008 06:00 to Mon 02 Jun 2008 06:00 UTC
Issued: Sat 31 May 2008 22:36
Forecaster: SCHLENCZEK

SYNOPSIS

An upper level cut off low centered over the Bay of Biscay will picked up by a longwave trough west of Ireland during the period. Ahead of this upper low, a 45 m/s jet streak at 300hPa over western France / northeastern Spain will translate northward while weakening. An upper ridge that stretches from Libya towards Scandinavia will slowly move eastward. Very warm and moist air remains over a large area between southern Italy / Greece in the south and Germany / Poland in the north. Cold and dry air should be in place over northeastern Europe while cool and moist maritime air overspreads southwestern and western Europe.

DISCUSSION

...Eastern France...

Some hundred J/kg of CAPE will form in the afternoon on the right side of the jet axis. About 15 to 20 m/s deep layer shear should be in place and organized multicells may develop, posing a threat of isolated large hail. In the late afternoon, an upper level vort max should overspread the region and a MCS may form. About 20 m/s at 700hPa suggest that isolated severe gusts may occur.

...Northern / northeastern Germany, Czech Republic, Slovakia, Hungary, northwestern Romania...

Although vertical shear is rather weak (less than 15 m/s deep layer shear), some organized storms with isolated large hail may develop in an environment with about 1,5 kJ/kg MLCAPE. A marginal level-one threat seems to be warranted. Storm may persist for several hours over some regions which leads to an enhanced flash flood threat.

...Western France, northern Spain...

Low-end to moderate instability should be present in the vicinity of the upper low in the afternoon. Weak vertical shear should preclude severe weather but an isolated large hail report is not completely ruled out. Steep LL lapse rates and low LCL heights suggest that an isolated funnel / short-lived tornado is not ruled out either but overall threat appears to be too low to warrant a level-one. Thunderstorms should diminish after sunset as the major part of CAPE is surface-based and forcing is rather weak.
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