Storm Forecast
Valid: Thu 11 Nov 2010 06:00 to Fri 12 Nov 2010 06:00 UTC
Issued: Wed 10 Nov 2010 14:05
Forecaster: GATZEN

A level 1 was issued for the Greece region mainly for large hail.

A level 1 was issued for the North Sea region and the Benelux region mainly for severe wind gusts and tornadoes.

SYNOPSIS

A long-wave trough is placed over Europe yielding a deep south-westerly jet across the east Mediterranean. In the wake of this trough, an intense frontal zone will expand rapidly eastward. This will be associated with increasing geopotential over Europe, and the long-wave trough will weaken and moves east. At the end of the period a cut-off low is expected to remain over the southern Mediterranean Sea.

DISCUSSION

Greece region

A frontal boundary is present at the eastern flank of the long-wave trough that will slowly move eastward during the period. Ahead of this front, warm air advection is expected from the African desert. The warm air mass is rather dry at low-levels and will tend to be stable. Along the frontal boundary, increasing boundary-layer moisture is forecast and CAPE is expected to develop. Low-level convergence along the cold front will assist thunderstorm development to the west of Greece during the day. Although the low-level wind field is rather weak, favourably veering profiles are expected and some storms may evolve mesocyclones capable of producing large hail. Main convective mode will be multicells in the strongly-sheared environment with 25 m/s 0-6km bulk shear. The potential for severe weather seems to be quite weak and only isolated wind/tornado events are forecast.

In the evening and night hours, the convective activity will likely spread eastward. Models suggest increasing low-level moisture over the Aegean Sea that will lead to CAPE. Initiation is rather questionable as QG forcing will be weak to the north of the developing cut-off low. However, storms that form may be capable of producing large hail given the strong deep layer vertical wind shear.

North Sea and Benelux region

An intense low pressure system will affect western Europe on Thursday. A strong mid-level jet streak reaching 60 m/s at 500 hPa will spread into northern Germany and Poland late in the period. At low levels, a low-level jet will evolve over France and Germany during the day. Latest models indicate that an occlusion will move over the North Sea in the evening hours. While the mid-level temperatures will decrease, neutral lapse rates are forecast over the North Sea. Along the occlusion, strong forced ascend is expected to support a narrow cold-frontal rain band that will move across northern Germany and Poland during the night. The potential for some thunder will increase near Denmark where rather low equilibrium level temperatures are expected. Given the strong low-level vertical wind shear, severe wind gusts are possible.

Farther south, the narrow cold frontal rain band will be rather shallow and is not expected to produce thunder. However, severe wind gusts and isolated tornadoes are not ruled out given the strong low-level vertical wind shear.