Forecast Update
Valid: Wed 14 Oct 2009 17:00 to Thu 15 Oct 2009 06:00 UTC
Issued: Wed 14 Oct 2009 16:45
Forecaster: SCHLENCZEK
A level 1 was issued for S Turkey mainly for tornadoes and excessive precipitation and to a lesser extent for large hail.
A level 1 was issued for most parts of the Tyrrhenian Sea mainly for tornadoes.
A level 1 was issued for S Greece mainly for excessive precipitation.
SYNOPSIS
The upper flow pattern shows a stout ridge over the western and southwestern portions of Europe and an upper trough over Hungary which will dig southward. Between those features, a strong northerly upper level jet is present and CAA at lower levels will continue, leading to cold conditions with graupel and snow in the mountaneous parts of Germany, Poland and the Czech Republic and also in large parts of SE Europe. Ahead of this trough, a 992hPa surface low over E Poland is moving to the NNE with a well-defined cold front stretching from the W Black Sea via SE Ukraine towards W Russia and E Belarus. In the warm sector, a lot of moist and warm air is advected into parts of Russia with dewpoints in the lower tens and temperatures in the lower twenties. In the vicinity of the warm front, easterly winds near the surface enhance LL shear and SRH in this region.
Cyclogenesis near the southern tip of the upper trough over the eastern Mediterranean should be most important for severe convective storms on Wednesday. The airmass located in this region is moderately warm and very moist with dewpoints in the upper tens / lower twenties by 14 UTC surface observations. 12 UTC soundings show a near dry adiabatic layer from 850hPa up to 600hPa which may aid in production of reasonable values of MLCAPE.
Over the central Mediterranean, recent observations and satellite imagery show cyclogenesis between Sardinia and Sicily. Mid level lapse rates will steepen as CAA at upper levels continues. Dewpoints in order of 12 - 14°C near the surface are observed which results in a few hundred J/kg MLCAPE. Recently, isolated to scattered thunderstorms are present in the Tyrrhenian Sea / C Mediterranean.
DISCUSSION
...Tyrrhenian Sea, C Mediterranean, parts of Italy...
Near the cold core of the upper trough, steep mid level lapse rates and sufficient moisture in the boundary layer lead to some hundred J/kg CAPE. Especially near the upper jet streak over the Tyrrhenian Sea, deep layer shear in order of 30 m/s is expected and some storms should be well-organised. Storms may be accompanied by marginally severe hail and gusty winds but due to steep LL lapse rates and slightly enhanced values of SRH, also some tornadoes may occur. As most of the instability originates from the boundary layer, convective activity will decrease in the evening hours. Nevertheless, a level 1 threat for tornadoes should be warranted.
...S Turkey...
Over the E Mediterranean, a plume of very moist and unstable air with almost uncapped MLCAPEs around 1 kJ/kg is advected towards S Turkey. Near the coastline, easterly LL winds are observed. Given LL shear in order of 10 m/s and up to 20 m/s deep layer shear in an environment with 100 - 150 m²/s² SRH1, discrete storms may tend to develop rotating updraughts and also tornadoes. As the strong LL moisture convergence persists along the coastal regions, excessive precipitation may occur and flash floods are possible. Isolated large hail is not discounted either but tornadoes should be the main threat.
...S Greece...
Recently, a convective cluster is forming between Sicily and Greece, moving towards SW Greece during the evening / night hours. As an approaching shortwave trough will provide some QG forcing and instability is forecast not to decrease during the night, this system should strengthen and will pose a threat of excessive precipitation in extreme SW Greece. QPF in order of 50mm / 12hr and enhanced values of effective PWAT are forecast by GFS and therefore a level 1 was issued for this region.
