Storm Forecast
Valid: Sun 11 May 2008 06:00 to Mon 12 May 2008 06:00 UTC
Issued: Sat 10 May 2008 22:41
Forecaster: SCHLENCZEK

SYNOPSIS

A weakening upper level cut off low over the Balearic Islands remains almost stationary. At its southern flank, a jet streak with 40 m/s at 300hPa moves across northern Algeria. The British Isles and large portions of central Europe are dominated by an upper high. Accumulation of rich BL moisture will lead to instability at the southwestern flank of the upper high.

Another upper low will lead to unsettled conditions over Belarus and Poland. A small 30 m/s jet streak at 500hPa associated with this low will cross eastern Poland during the afternoon.

DISCUSSION

...Northeastern Iberia...Balearic Islands...

Underneath the upper low, steep mid level lapse rates and rich BL moisture will lead to some hundred J/kg of CAPE. 0-6 km deep layer shear is expected to stay below 15 m/s which minimizes the chance for severe convection. Some multicells may develop and an isolated large hail report is not ruled out. The region with CAPE in order of 500 J/kg should spread northeastward towards northern Italy during the evening.

... East-central France...

Rich BL moisture has accumulated over central France which will result in about 1,5 kJ/kg MUCAPE. A surface low is forecast to develop over southeastern France and western Switzerland and upward motion due to the convergent LL wind field should lead to widespread convection. Even though vertical shear is very low, isolated large hail is not ruled out as steep mid level lapse rates create strong buoyancy. Storms may persist for several hours in this region which may lead to flash floods.

...Eastern Poland...Belarus...

Ahead of the upper low, a few hundred J/kg of CAPE should be present in an environment with 20 to 25 m/s deep layer shear. As the upper level vort max moves southwestward, organized multicells will develop with isolated large hail being the main threat. Some of them may contain short-lived mesocyclones. As CIN is rather low, storms will tend to cluster and severe threat should decrease during the evening. A level-one threat should be marginally warranted, though.

...British Isles...

About 1 kJ/kg MUCAPE should be present in the warm and moist airmass over southern UK and diurnally driven thunderstorms will develop. The kinematic environment is rather weak but diurnal heating may create steep LL lapse rates. As LCL heights are expected to be rather low, an isolated funnel / brief tornado is not ruled out. However, tornado threat seems to be too low to issue a level-one threat.

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