Storm Forecast
Valid: Wed 01 Sep 2010 06:00 to Thu 02 Sep 2010 06:00 UTC
Issued: Wed 01 Sep 2010 06:33
Forecaster: PUCIK

A level 1 was issued for Central Spain mainly for marginally severe hail and wind gusts.

A level 1 was issued for Northern Algiers mainly for severe hail and wind gusts.

A level 1 was issued for the Black Sea and its adjacent coastal areas mainly for large hail, severe wind gusts and to the lesser extent for tornadoes.

A level 1 was issued for Central Ukraine mainly for marginally severe hail and excessive precipitation.

SYNOPSIS

The main macrosynoptic feature at mid-levels is a deep trough with its axis stretching from Scandinavia to Southeastern Europe. It involves double centers - one will be located over Northern Finnland and another one over Northern Romania/Western Ukraine at 12 UTC. Strong flow surrounds this trough, especially at its southern and eastern flank. To the west a complex pattern prevails with an insignificant ridge covering parts of Western Europe, such as British Isles, whereas a shallow trough will move over the Iberian penninsula during the forecast period.

Closer to the surface, a deep low pressure system will only slowly progress eastwards over Eastern Europe, centered over Ukraine and the Black Sea as of 12 UTC. Strong wavy frontal system will be associated with this low. High pressure system will stall over much of Northwestern Europe while to south a shallow low will be observed over Spain.

DISCUSSION

...Central Spain...

With the favorable PVA from the approaching trough and abundant low level flow convergence, daytime heating will likely result in the destabilisation with MLCAPEs possibly locally exceeding 1000 J/kg. Numerous thunderstorms are expected to form over Spain with little CIN to supress the storm development. Low end Level 1 is introduced for the region, where the stronger flow at mid and upper levels of troposphere is simulated and wind shear will reach at least moderate values, of 15-20 m/s in 0-6 km and the same in 1-8 km layer during the evening hours. With enhanced shear, better storm organisation might result in an occurence of marginally severe hail or wind gusts with the stronger cells.

...Northern Algiers...

Strong westerly flow at mid and upper levels of troposphere should result in the high wind shear values, over 25 m/s in 0-6 km layer, which is sufficient for sustaining very well organised convection. Models GFS and ECMWF also agree on the low to moderate destabilisation over the region, with the highest values of CAPE probably being observed close to the coastal areas. Nevertheless, only spotty precipitation fields and no hints of clear concentrated forcing suggest that initiation will probably be only isolated. Level 1 is introduced for the region with the highest probability of storm occurence. In strong wind-shear, supercellular convection might develop with threats of severe hail or severe wind gusts.

...Black Sea, Ukraine...

Ahead of the deep trough, in the strong southerly flow reaching over 25 m/s at 500 hPa, cold front slowly progresses to the east. Favorable synoptic scale forcing is forecast, especially over the region of Black Sea and its adjacent coastal areas. The same will also be true for the destabilisation - moderate to high values of CAPE are forecast over the Sea and its coasts. Likely contribution to such CAPEs is a strong WAA at the low levels, high moisture content over the sea and cooling midlevels. Overlaid by strong wind shear, reaching over 25 m/s in 0-6 km layer and also enhanced SREH, high potential will exist for well organised storms, including supercells with threat of large hail, strong wind gusts and especially in the morning and late evening hours, tornadoes are not ruled out either thanks to LLS exceeding 10 m/s. The highest potential will exist out of our forecast area, over central Black Sea, where a Level 2 would be probably necessary. Towards the north, in declining instability and its shift to a more "elevated nature" - threat will shift to marginally severe hail and excessive rainfall, as flow seems to be be almost parallel to the frontal system with chance of back-building or a repetitive cell training over certain areas.