Storm Forecast
Valid: Fri 01 Jun 2007 06:00 to Sat 02 Jun 2007 06:00 UTC
Issued: Thu 31 May 2007 21:23
Forecaster: TUSCHY

SYNOPSIS

Taking a glanze on the latest satellite images exhibits a disturbed weather pattern over Europe.
A fierce cold front takes a constantly better shape as increasingly colder and drier air gets advected towards the southeast / east. The main and most progressive part of this front will be active well outside of the forecast area so no closer examination will be needed.
Two more or less pronounced upper-level disturbances over parts of central Europe will bring unsettled but warm conditions.
A groundbreaking synoptic evolution for the next few days ( regarding a possible blocking pattern ) will be underway as strong WAA downstream of a north-Atlantic trough will strengthen ridging over NW Europe, which also affects strong high pressure situated over N-Europe.

DISCUSSION

...Parts of Poland, Belarus, Hungary, Slovakia, Romania and Ukraine ...

A pool of marginal lowered geopotential heights drops off and slowly shifts towards the east towards the Black Sea region.
This weak trough can be barely seen on WV images, but can be tracked on latest 18 hours sounding loop and GFS seems to be on the right track.
Run-to-run inconsistency and gaps between models are strong but bit by bit it solidifies that the main activity can be expected along and northeast of the Carpathian Mountains.
A humid and moist airmass is forecast to enter the area from the east ( already during the morning hours ), spreading slowly towards the west. Not impressive but at least moderately steepened mid-level lapse rates will be present, too.
Main concern will be the gradual warm-up mainly at lower and mid-levels and possibly convective debris from nocturnal convection, but diabatic heating and WAA should be enough to erode the cap as early as the late morning hours.
A moderately unstable airmass,DLS in the order of 10-15m/s and scattered storms will develop with an isolated large hail risk, regarding the enhanced helical flow.
Low LCLs and locally augmented LL shear also enhance the tornado threat although widespread storm coverage / expected rapid clustering should limit the threat.
Thunderstorm activity should gradually increase during the afternoon hours as strong vort max will cross the area from the south and a convective system will evolve.
Severe wind gusts and an isolated tornado will be a threat with this slowly northwad moving activity but weak steering flow and repeated thunderstorm evolution should support the flash flood threat to be the main threat.

....Italy....

A leisurely southward shifting upper-level low pressure area and a weakly capped environment will be present and supportive for widespread thunderstorm evolution.
Weak shear and a moderately unstable airmass will favor a mixture of pulsating / multicell storms with an isolated large hail risk and gusty wind gusts. A broad level-1 area was anticipated to be the best solution for reflecting the selective occurence of storms producing strong to severe weather.

DLS over south-central Italy will increase during the evening hours and a combination of an approaching cold front and a streak from the NW favor the possible evolution of an organized cluster of storms due to enhanced forcing.
A few severe wind gust reports and hail matching locally our severe criteria will be the main threat.

...SE-Germany...

A southeastward moving upper-level system just west of the Alpes and a shaping and rapidly sharpening baroclinic zone will set up over S-Germany. Alignement of this boundary and lowering surface pressure over SE Bavaria will help to infiltrate a cooler airmass over S-Germany towards from the west.
Markedly strengthening cap could be eroded by diabatic heating, but right now confidence is more conservative that more than a few storms will be able to develop.
Nice lapse rates and some SRH3 could be enough for an isolated large hail report.

During the afternoon and early evening hours a possibly marginal severe line of storms should start to cross the extreme S-Germany from the west towards the east with an isolated severe wind gust and large hail threat.
The small level area should reflect the possibility of an isolated hail event matching our severe criterion. Enhanced SRH3 values and mid-level lapse rates approaching 7K/km support this low-end threat although DLS will be low ( between 10 and 15m/s ).

A belt of higher mixing ratios also covers parts of central Austria and a few storms can be expected. Absence of any shear should keep any storm short lived and subsevere.

...Parts of extreme western Russia...

Strong to severe thunderstorms will be expected along the slowly southward moving cold front. A combination of enhanced DLS , moderately instability release and nice lapse rates favor the risk for a few severe wind gusts / large hail reports. A better environment for more widespread severe weather should evolve east of our forecast area.