Storm Forecast
Valid: Wed 18 Apr 2012 06:00 to Thu 19 Apr 2012 06:00 UTC
Issued: Tue 17 Apr 2012 20:52
Forecaster: SCHLENCZEK

A level 2 was issued for W Turkey for severe wind gusts, excessive convective precipitation and tornadoes and to a lesser extent for large hail.

A level 1 surrounds the level 2 for severe wind gusts and tornadoes.

A level 1 was issued for W and NW France mainly for severe wind gusts and an isolated tornado.

SYNOPSIS

There are three well-defined cyclonic vortices over the European region which may be associated with deep moist convection on Wednesday: One low pressure system is initially centered over the Irish Sea and moves eastwards towards Benelux and Germany. The second low crosses the Baltics and eastern parts of Scandinavia and continues towards the Barents Sea. The third low is located over the Aegean Sea and moves rapidly northeastwards into the Black Sea region.Intense gradient winds within the boundary layer are expected over the eastern Mediterranean region and over western Europe.

DISCUSSION

...British Isles, France, Benelux, W Germany...

Near the center of the low pressure system, a strong gradient flow will persist through the day. Given some hundred J/kg of uncapped MUCAPE and EL temperature in order of -30°C, showers and thunderstorms are likely to occur in this area. Wind speeds in order of 20 - 25 m/s at 850 hPa and 0-3 km shear around 15 - 20 m/s are fairly enough for some organized multicellular lines and clusters which may produce isolated severe wind gusts. A tornado is not ruled out either as LL shear in order of 15 m/s is present and 0-3 km SRH is also enhanced. According to the GFS model, the tornado threat is maximized along the coastline of W and NW France. The peak activity is expected in the early afternoon as most of the CAPE is tied to the diurnal cycle.

...Greece, Crete, Aegean Sea, Bosporus region, W Turkey...

Unstable air is present ahead of the low pressure system which should approach W Turkey around noon. A narrow region of the cold front shows an overlap of very strong deep layer shear (30 - 40 m/s), 300 - 400 m²/s² of SRH3 and a few hundred J/kg CAPE. As both GFS and HIRLAM show strong precipitation signals, convective initiation has to be expected. Under such environmental conditions, organized multicells and a few possible supercells will tend to merge into a MCS. Shortly after initiation, an isolated tornado and large hail threat should be prominent. The more severe threat is to be expected with a developing linearly-shaped MCS, which is likely to produce widespread severe wind gusts and excessive precipitation. This is a borderline LVL2 situation as instability is rather limited, but overall parameters show a high probability of severe weather for W Turkey and surrounding regions.

High SRH values and some instability is also found over Crete in the wake of the cold front. A slight chance for severe wind gusts and tornadoes is expected and therefore a LVL1 is issued.