Storm Forecast
Valid: Fri 01 Apr 2011 06:00 to Sat 02 Apr 2011 06:00 UTC
Issued: Fri 01 Apr 2011 01:05
Forecaster: TUSCHY
A level 1 was issued for parts of the Aegean Sea, Turkey and Crete mainly for large hail and isolated severe wind gusts.
SYNOPSIS
A pattern change is underway with a large-scale trough gradually evolving over the far eastern Atlantic and a major ridge arching northward over W/CNTRL Europe. In fact, the GHGN index reveals the development of a deep warm anomaly over W-Europe throughout the period and onwards. Another trough over SE-Europe gradually moves off the east with marginal changes in strength and tilt. Finally, a progressive impulse over Sweden/Norway (Friday noon) gets caught within northeastward building height rises and this feature weakens betimes.
DICUSSION
... N-Portugal and NW-Spain ...
Latest SSMI/AMSRE data already indicates a plume of subtropical air ahead of a consolidating cold front, which
affects the forecast area during the night hours. However, this plume fans out as it approaches the coast, resulting in decreasing TPW values of 25-30 mm, probably even lower while spreading onshore. Model consensus is reasonable showing an increase of the dewpoints over the highlighted area, especially at 18 Z onwards. Air mass remains capped most of the time until late the night. As front moves in (Sa, 00Z onwards), weak PVA atop increasing frontogenetical forcing may assist in the development of an isolated thunderstorm, mainly along the mountainous areas. Forecast soundings reveal some elevated CAPE with shear magnitude increasing from 15 or 20 m/s (15Z) to 30 m/s (00Z) with some directional shear, but current thinking is that shear/instability fields remain mainly displaced throughout the period. Mid-level lapse rates increase, but warm 0-3 km layer may keep hail growth limited (despite model progs approaching severe criterion). No level will be issued.
During the night, strong moisture advection is forecast all the way to the UK with low-end MUCAPE developing up to the W-English Channel. Would not be surprised to see an isolated short-lived thunderstorm event that far north, but overall coverage/lifetime of thunderstorms will be too marginal for any highlighted area.
... S-Aegean Sea and Turkey ...
A classic set-up for the E-Mediterranean for organized convection as large-scale upper trough shiftes eastwards with a gradually consolidating LL depression. This time, the depression remains disorganized, which may keep severe probabilities below the threshold "widespread severe". However, good moisture advection beneath cooling mid-levels results in 500 - 1000 J/kg MLCAPE with highest values offshore/along the coast. Forecast soundings indicate good veering within broad CAPE layer and a nice overlap of shear/instability within the hail growth zone. Hence, multicells/isolated supercells are probable with large hail/isolated very large hail being the main hazard. Dependent on the strength of the LL depression, 0-3 km shear may increase to 15-20 m/s, which may also support a severe wind gust risk, however there are no hints on a significant deepening of the LL depression right now. Thunderstorms cluster betimes with locally heavy rainfall. They keep going all night long...mainly offshore.
... Central Europe ...
Weak CAPE fields evolve over parts of Germany, Austria, the Czech Republic and Poland during the daytime hours. 15 m/s DLS may assist in better organized updrafts, but current CAPE forecasts are not really impressive for longer lived thunderstorm events. Hence, a few short-lived thunderstorms between noon/evening are expected. No severe is forecast.
