Storm Forecast
Valid: Wed 17 Sep 2008 06:00 to Thu 18 Sep 2008 06:00 UTC
Issued: Tue 16 Sep 2008 21:39
Forecaster: PUCIK

SYNOPSIS

A blocking pattern persist over most of Europe, as a large surface high pressure system has settled over most of the NE part of Europe, advecting a polar continental air mass into Middle Europe and even the Medditerranean. In the mid-troposphere a deep trough with a cold core low in the middle is rotating over SE Europe . Around this feature, a strengthened flow exists, with 25 m/s windspeeds at 500hPa level. A shallow, but large surface cyclone which is associated with the frontal zone, extending from Greece to Ukraine will move only very slowly during the forecast period. As the cold front should strenghten when passing over the warm waters of Black Sea, depression is forecast to deepen slightly. As most of Europe is under CAA and stable conditions, only SE Europe and SW. The Mediterranean should experience a warm air intrusion and at least partially unstable troposphere.

DISCUSSION

...Black Sea region...

A warm and humid airmass should be present over the region during the forecast period. Models show also steep mid-level lapse rates overspreading the pre-frontal areas and thus, together with humid airmass, yielding moderately unstable environment. GFS is showing more than 2000 J/kg of MLCAPE over the region. However, these values might be exaggerated by presence of very humid airmass just over the sea waters, which might be mixed out prior to the convection development. Enhanced mid-level flow will sustain DLS values in order of 20 - 25 m/s, with shear in the lowest 3 kms between 15 - 20 m/s. These values are favourable for development of well-organised thunderstorms, including supercells. Backing low level wind-field, induced by the passage and slight deepening of surface cyclone should enhance SREH values in the evening, when MCS is forecast to pass the region. Values could be locally exceeding 200 J/kg and therefore, increasing chance for the development of rotating updrafts. Storms should be present in the region from early morning and will persist well into the night, supported by unstable conditions and large scale lift, induced by mid-level trough. In the morning, most of the convection should be confined to SW. part, with severe weather threats being tornadoes/waterspouts ( LLS over 10 m/s and low LCLs) or isolated large hail/ severe wind gust event. If supercells manage to develop during the day, large to very large hail is possible with any such cell as high CAPEs and steep lapse rates enhance this threat. Severe wind gusts are possible too. Very strong convergence signals and parallel flow to the frontal range suggest that MCS will form by the evening ( 18Z) and will move NE-wards across the region. Large hail should be the primary threat at first, then changing to marginally severe wind gusts, as low level wind field will strenghten with MCS moving over the N part of LVL 2 region. One or two tornadoes/waterspouts should also be possible as LLS will exceed 10 m/s and SREH0-1 km 200 J/kg.