Storm Forecast
Valid: Tue 28 Sep 2010 06:00 to Wed 29 Sep 2010 06:00 UTC
Issued: Mon 27 Sep 2010 23:30
Forecaster: KOROSEC

A level 1 was issued for eastern Ukraine and western Russia mainly for strong wind gusts and marginally large hail.

A level 1 was issued for southern Mediterranean, parts of Algeria, Tunisia and parts of extreme southern Italy mainly for excessive rainfall, large hail, strong wind gusts and tornadoes.

SYNOPSIS

A large upper low over central Europe finally makes progress towards east during the forecast period. Two larger vorticity maxima will be embedded in this low, one places just south of Baltic states and another one moving from northern towards central Italy. At surface, rather large surface pressure system is placed over NE Europe and gets pushed towards Russia as the upper low moves further east. A surface front extends from this surface low southwards across extreme western Russia and rapidly shifts east.

... Eaatern Ukraine into Western Russia ...

Ahead of the eastwards advancing cold front, WAA pushes marginally unstable airmass into western Russia. Several hundreds of MLCAPE seem reasonable to release, as supported by the models. A rather limited large scale ascent suggests that widespread activity is not likely. However, isolated to scattered convective storms should still form. Given the around 10-15 m/s of deep-layer shear in place, mostly multicells can be expected, while rotating storms seem limited given the lack of SR helicity and LL shear/backing flow. The main threat with these storms should be strong wind gusts where the strongest cells could support some marginally large hail as well.

... parts of Northern Africa and Southern Mediterranean sea ...

A baroclinic zone streches from Northern Africa into southern Mediterranean. Rich BL moisture will be in place over southern Mediterranean sea (GFS pushes mixing ratio well above 16 g/kg) and high instability is expected. Rougly between 1500 and 2000 J/kg. With several near surface convergences, scattered storms will form. Ahead of an approaching trough from the north, a strong mid-level jet created environment of moderate to strong shear. Around 25-30 m/s should be easily available and support well organized storms. Those should combine numerous multicells as well as a few supercells. Severe storm with threat for large hail, strong wind gusts, a few tornadoes and intense rainfall can be expected locally. Any cluster could locally increase the rain amounts as well.

As the central European trough/low moves towards SSE, a DCVA on its back side moves from northern to central Italy. Enough ascent on its front side should support storm initiation along the eastern Ligurian sea where marginal instability will exist. 15-20 m/s of deep-layer shear will be available as well, which should be enough for some organized storms, although their coverage will not be too widespread. However, some strong wind gusts and intense rainfall should be their primary threat.

Warm SSTs and steep LL lapse rates over Liguarian sea, north-central Adriatic sea, as well as southern Mediteranean could also bring some threat for waterspouts. But with rather low probabilities, a threat level is not warranted.