Storm Forecast
Valid: Sun 29 Jun 2008 06:00 to Mon 30 Jun 2008 06:00 UTC
Issued: Sat 28 Jun 2008 22:55
Forecaster: SCHLENCZEK

SYNOPSIS

At Sunday 06 UTC, an upper level cut off low over the Northeast Atlantic will be the focus for fast cyclogenesis at its southwestern edge. The developing low pressure system will lead to strong WAA over western and central Europe in the following days. A weak upper trough over the Baltic Sea will lead to a cut off low over western Russia on Monday. At upper levels, an almost zonal jet with some embedded shortwaves and speed maxima around 45 m/s at 300hPa stretches from NE Canada to the Black Sea. A weak upper trough west of Portugal should move eastward during the day. A weak low pressure region at upper levels will remain oer the eastern Mediterranean. A plume of high theta-e is present over Iberia, southern France and Italy on the warm side of a deep layer frontal zone.

DISCUSSION

...Iberia...

During the afternoon, a vort-max ahead of the upper trough should overspread the region where some hundred J/kg of CAPE are present. Slightly enhanced (150 J/kg) SRH3 hints at possible mesocyclones with an attendant large hail threat. Isolated severe gusts are not ruled out as mid levels are very dry which is favourable for downdraft acceleration due to evaporative cooling. Rather weak precipitation signals in GFS 12 UTC and GFS 18 UTC show that storms should develop more isolated. A small level-one area should be warranted, though.

...France, Italy, Switzerland...

Contrary to the thermodynamic environment over Iberia, instability over France and Italy should be more robust with about 1,5 kJ/kg MUCAPE. Vertical shear is expected to stay well below 15 m/s but locally enhanced shear at lower levels could provide about 100 J/kg SRH3. Isolated organized multicells and perhaps a supercell may develop, posing a threat of large hail and severe gusts. Low LCL heights and good LL buoyancy suggest that a funnel / brief tornado are not completely ruled out. Thunderstorm activity should weaken after sunset as the major part of CAPE is surface-based.

... Southern Scandinavia, Finland, Baltic States...

Ahead of a weak upper trough, diurnal heating should provide some hundred J/kg of CAPE during the afternoon. Showers and thunderstorms are expected to develop. Some of them may be accompanied by small hail and gusty winds but severe weather is not expected. Steep LL lapse rates show that an isolated funnel / brief tornado is not ruled out but a level area is not warranted at the moment.

Another region with rather weak CAPE and moderate (20 m/s) DLS is expected over the North Sea / Denmark / northern Germany in the late evening. Some thunderstorms should develop but severe weather appears rather unlikely.
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