Storm Forecast
Valid: Sun 07 Jun 2009 06:00 to Mon 08 Jun 2009 06:00 UTC
Issued: Sun 07 Jun 2009 06:27
Forecaster: SCHLENCZEK

A level 2 was issued for W Ukraine, SW Russa and SE Belarus mainly for strong tornadoes, large hail and damaging gusts.

A level 2 was issued for SE Austria, E Slovenia and SW Hungary mainly for damaging gusts and large hail.

A level 1 surrounding both level 2 areas was issued for Italy towards S Balkans, SW Russia, N Belarus, SE Poland and E Austria mainly for large hail and severe gusts.

A level 1 was issued for NE France, S Belgium and W Germany mainly for tornadoes and severe gusts.


SYNOPSIS

Between a ridge over the eastern Mediterranean and a large upper trough over central Europe, hot and moist air is advected into parts of eastern and southeastern Europe. Numerous imbedded vort-maxima will cross northwestern - central Europe and also parts of eastern Europe during the period. One of the dominant upper level disturbances should be located over eastern Poland on early Sunday morning and will translate northeastward into western Russia till Monday.

Another well-defined low pressure system over the East Atlantic is forecast to move southeastward towards the Iberian Peninsula, affecting NW Portugal in the second half of the forecast period.

A cold and more stable airmass over Scandinavia will be advected southward towards northern Germany during the period. Some thunderstorms should be possible in the vicinity of a weak cold front that will cross NE France and W Germany on Sunday afternoon.


DISCUSSION

...W Ukraine, S-central Belarus, SW Russia...

In the warm sector of a low pressure system located over eastern Poland, moderately unstable air with 500 to 1500 J/kg MLCAPE will be advectd into W Ukraine and Belarus. 00 UTC soundings from SW Ukraine show remnants of an EML which provides some weak capping in the western part of the level 2 area. Even near the center of the surface low, GFS predicts some low-end instability - almost uncapped but located in a very favorable kinematic environment. Model guidance hints at deep layer shear in order of 25 m/s in most parts of the Ukraine with very strong LLS and SRH1 / SRH3 increasing towards the warm front which extends from the S Baltic States into W Russia. Sufficient lift is provided by an upper vort-max that is forecast to cross the area of interest in the late morning / early afternoon hours.

Right now, remnants of the convective systems that developed yesterday evening over the N Balkans move across eastern Europe and the cloudiness at mid levels will hinder insolation which results in smaller MUCAPE than anticipated. Nevertheless, convective initiation is very likely as shown by simulated CAPE also in the vicinity of the stratiform precip regions in the level 2 area and almost every storm should be capable of producing large / very large hail and damaging gusts. The main fraction of storms that will develop is expected to be long-lived supercells that may also produce some possibly strong tornadoes. The threat of severe weather will continue until the late evening. Locally, excessive convective rainfall may lead to flash floods.


...extreme SE Austria, S Slovak Rep, Slovenia, Hungary...

In the wake of the intense low over Poland, moderate instability should be present after diurnal heating in the vicinity of a 35 m/s jet streak which stretches from Sardinia towards NE Hungary. Even though MLCAPE should be limited to values below 1 kJ/kg, any storm will profit from 30 - 35 m/s deep layer shear and organize into bowing line segments and supercells, capable of producing large hail and damaging gusts. A tornado cannot be ruled out but due to a lack of good LLS / SRH1 the tornado probability is significantly lower than in the level 2 area further downstream.

...large portions of Italy, including Sicily...

Very strong (25 - 35 m/s) DLS is forecast over Italy in a region with some hundred J/kg of CAPE. Some capping will still exist due to an EML advected from the N Sahara and initiation should depend on sufficient forcing. Vertical motion for ascent will have its origin in an upper vort-max over N Italy which is forecast to cross the affected region around midday. Storms should become well-organized multicells and supercells, capable of producing large hail and severe gusts. In the late afternoon / evening, the threat of severe weather will decrease as the boundary layer becomes more stable and almost all CAPE vanishes.

...NE France, W Germany...

Ahead of an approaching upper low over the Channel region, some hundred J/kg CAPE should be available. Deep layer shear should be best near the left exit region of a 30 m/s jet streak over NE France where strong QG forcing is forecast. Initiation will take place around midday and there will be some organized multicells and maybe also a few short-lived supercells. Rich BL moisture and about 10 m/s LLS will provide good conditions for a few tornadoes but strong tornadoes should be unlikely. Additionally, some marginally severe hail is possible and severe gusts due to downward transport of momentum are not ruled out as there are quite strong winds in the mid and lower levels.