Storm Forecast
Valid: Thu 08 Nov 2007 06:00 to Fri 09 Nov 2007 06:00 UTC
Issued: Wed 07 Nov 2007 21:56
Forecaster: GATZEN

SYNOPSIS

Well-developed polar frontal zone affects Europe during the period, with several intense short-waves traveling eastward. An amplified trough is forecast over east Europe that will move further east on Thursday, reaching from western Russia to central Turkey at Friday morning. Following short-wave ridge is expected to cross the central regions of Europe during the day. Another intense short-wave trough quickly propagates north-eastward over British Isles and North Sea region. Associated jet streak reaching 80 m/s at the 300 hPa-level will lead to strong QG forcing, and latest models indicate cyclogenesis in the range of the occlusion point of north Atlantic frontal systems. Affected air mass is rather stable with neutral lapse rates at best and relatively rich boundary-layer moisture over British Isles initially, and thunderstorms seem to be not very likely. Over the Mediterranean, northerly low-level winds in the wake of the east European trough have led to stable conditions as warm mid-level air spreads into west Mediterranean. Best potential for thunderstorms is forecast over the east Mediterranean Sea underneath the trough axis of the eastern trough.

DISCUSSION

East Mediterranean and Black Sea

Rather warm sea surface temperatures and mid-level cold air mass in the range of the trough center will likely create rather steep lapse rates as indicated by latest soundings that show relatively strong low-level buoyancy like at LICT Trapani. It seems to be reasonable that comparable low-level thermodynamics will spread eastward with the trough axis.

Over the Mediterranean, the region with instability is expected to be rather small and limited to the sea as indicated by latest model output. Although the vertical wind shear increases in the northern part of the instable region, veering with height seem to be rather weak and given mostly weak low-level buoyancy it is not expected that a favorable set-up for low-level mesocyclones and tornadoes will develop. To the south, weak vertical wind shear may be more favorable for a few waterspouts, but given weak low-level convergence and limited buoyancy, chance seems to be not too high either.

Over the Aegean and Black Sea, low-level buoyancy is forecast to be even weaker, limiting the chance for severe events.

North Sea region, British Isles

Along the cold front of the developing surface low pressure system, a rather moist maritime air mass is forecast to spread into British Isles. Neutral lapse rates and maybe weak positive CAPE are forecast. Given strong QG forcing and low-level convergence in the range of the cold front, a stratiform rain band with embedded convection is forecast. As instability will be restricted to low levels, thunder seems to be not likely. Best potential exists near the trough center moving across Denmark in the evening hours as well as over south Germany where upslope flow and a higher equilibrium level are forecast.

Given strong low-level vertical wind shear, a few tornadoes are not ruled out especially near the coasts, where low-level buoyancy and low-level vertical wind shear may overlap. Indications are too weak for a level 1 though.

Southern Baltic Sea

At Thursday morning rapidly propagating uppe jet streak affects southern Baltic Sea, where a few thunderstorms may form. Vertical wind shear will be rather weak in the range of the trough axis, and severe convection is not expected.