Storm Forecast
Valid: Wed 03 Apr 2013 06:00 to Thu 04 Apr 2013 06:00 UTC
Issued: Tue 02 Apr 2013 20:44
Forecaster: PUCIK

A level 1 was issued for Southwestern Iberia and Algiers mainly for excessive precipitation, marginally large hail and severe wind gusts.

A level 1 was issued for Turkey mainly for excessive precipitation and to the lesser degree also for the other severe weather threats.

SYNOPSIS

With dominant high pressure system covering much of Northern Europe, very stable conditions along with dry easterly to northeasterly flow prevent any DMC activity with exception being the southernmost extents of the continent. Here, two features of interest will provide some opportunity for the thunderstorm occurrence. The first being a cyclonic vortex approaching Western Iberia during the day, gradually filling in as the center of the low is detached from the upper level forcing. The second one will be a short-wave trough crossing the Aegean Sea with strong south to southwesterly flow from low to upper levels of troposphere. Between both features, very strong jet-stream will stretch across the Southern Mediterranean and Northern Africa.

DISCUSSION

... Southwestern Iberia and Algiers ...

Belt of a moderate southwesterly flow along the flank of the low aloft should boost DLS values to the range of 15 to 25 m/s, which will only marginally overlap with an area of low-end CAPE. CAPE should mostly be a result of cooler mid-level temps spreading eastwards along with the cyclonic vortex, but the area of steeper mid-level lapse rates will be advected mostly behind the stronger flow. Degree of the overlap will thus be a decisive factor in this situation. A low end level 1 is issued for a possibility of well organised multicells (or even very isolated supercells) posing a threat of marginally severe hail or wind gusts. Threat should exist mostly in the period between 09 and 15 UTC. However, even outside this time-frame, numerous rounds of DMC might affect SW coastline, increasing the threat for excessive rainfall.

... Turkey ...

A strong low-level jet, pronounced especially during the early morning hours will rapidly transport enhanced low level moisture to the north. A belt of CAPE in order of hundreds J/kg should be available over the eastern Aegean Sea as the strong forcing spreads over this moist airmass on the forward flank of the rapidly advancing trough. Forcing should be most pronounced over southwestern coastlines area with the strongest low-level convergence signals. Current thinking is that a rather large parallel-stratiform MCS might form with slow advective motion towards the east, backbuilding southwards. Excessive rainfall would be thus the primary threat, but actually, slight chance of any kind of severe threat will be present. This chance is strongly dependent on the overlap of CAPE and wind shear, as CAPE should be most pronounced over the sea while the wind shear over the inland areas. In case of the more isolated development, also marginally severe hail or wind gusts / tornadoes could be possible thanks to the strong DLS / LLS.