Storm Forecast
Valid: Wed 03 May 2006 06:00 to Thu 04 May 2006 06:00 UTC
Issued: Tue 02 May 2006 19:54
Forecaster: TUSCHY

SYNOPSIS

Highly amplified weather pattern continues over Europe with an impressive upper level trough over the NE Atlantic and another, more inactive, trough over eastern Europe.
The latter one will continue to infiltrate cool and stable air further towards the south... A weakening frontal system (Poland-Hungary) will be the focus for isolated to scattered storm development... Strongest acitivity should overlap with pool of best instability ( Slovakia and Hungary).... Main activity is expected well towards the east of best DLS, but there will be a marginal hail risk with strongest storms, which tend to develop further towards the west
(mainly over Croatia ).

Diurnal driven TSTM activity will go on mainly over the southern parts of Italy... Warming aloft should minimize TSTM activity further towards the north .

DISCUSSION

...most parts of Spain, the Strait of Gibraltar and eastward...

Models forecast a broad trough to slide towards the NE, crossing the area of interest during the forecast period... Latest satellite loops indicate that models like GFS master the situation pretty well ( with impressive subtropical jet presentation and landfall of the core along the W-coast of Morocco)... Main concern for severe TSTM development/ ongoing storms will be during the morning and noon hours mainly over the level 1 area...
Closed low-level depression consitently forecast to develop east of the Strait of Gibraltar, moving slowly towards the east and starting a weakening trend from the noon hours onward.
Despite the fact that shear parameters will ease pretty fast over the level 1 area, models indicate convective development/ ongoing storms in an environment with up to 20m/s DLS and enhanced LL shear... Instability will be confined to the coastal areas and offshore, where storms will be surface based... Current thinking is that storms will already have clustered and therefore tornado possibilities will be limited ( mainly with more discrete cells), but main risk will be a severe wind gust/ isolated large hail risk.
Storm coverage should slowly decrease during the late morning hours such as severe threat will do.

Scattered TSTMs should also develop over most parts of Spain as a consequence of widespread moderate instability release....kinematic parameters too weak for an organized severe weather threat, but don't want to exclude an isolated large hail report with stronger storms ( e.g. NW Spain/N-Portugal).


...N-France, Belgium, the Netherlands, extreme NW Germany and most parts of United Kingdom...

Complex forecast scenario unfolds for parts of southern Great Britain and parts of this highlighted area could need an upgrade later on.
Main focus for TSTM development will be a warm front, which should move northward during the late evening hours.
Diurnal heating and frontogenetic forcing should be enough for isolated to scattered TSTM development along the frontal boundary...DLS in the order of about 10-15m/s and up to 800 J/kg instability will be enough for an isolated large hail / severe wind gust threat ( mainly over N-France and Belgium ).

A southward digging trough west of France will help to turn the wind field in the mid-/upper- levels more towards the SW and this will support a slowly northward propagation of aforementioned warm front.
Main concern is airmass quality and diminishing instability, but conditions look alright for at least isolated TSTM development...Increasing LL and DLS would pose an hail risk with stronger storms, but current uncertainties preclude higher probabilities.