Storm Forecast
Valid: Tue 05 Feb 2008 10:00 to Wed 06 Feb 2008 06:00 UTC
Issued: Tue 05 Feb 2008 10:04
Forecaster: GROENEMEIJER/TUSCHY

SYNOPSIS

Tuesday at 08:00 UTC... a westerly Jet is located over the Atlantic Ocean southwest of the British Isles. A low pressure system over northern Ireland is moving eastward slowly. South of the low, a broad warm sector over southern England and western France is advected eastward. Over SE Europe, a mid/upper cut-off low moves from southern Italy to Crete.

DISCUSSION

Southern Britain, Benelux countries, Northern France, West Germany...

At 08:00 UTC, the warm front, forming the leading edge of the warm moist air, stretched from the southern North Sea via Dunkirk to Nantes. Behind it, a strong west-southwesterly low-level jet, with wind speeds between 25 and 30 m/s, advects this airmass northeastward. A few hundreds of J/kg CAPE are forecast within almost the entire warm sector per GFS. The 06 UTC sounding of Valentia, Ireland, supports this prediction, indicating steep low-level lapse rates and almost 200 J/kg CAPE.

A jet streak over the Atlantic Ocean is moving eastward. The left side of its exit region is expected to overspread southern Britain during midday. As a result, forcing for upward vertical motion should increase and scattered convection is expected to ensue over southern England during the afternoon. The strong (near 15 m/s) 0-1 km shear, deep layer shear around 30 m/s suggest that convection will rapidly organize into small lines and possibly a few low-topped supercells. These will have a threat of producing a few severe wind gusts, small hail, and more importantly, a few tornadoes.

A second impulse of upper-level forcing should start to affect the Channel region during the second half of the evening. As a result, the coverage of convection will likely increase over the English Channel, northern France and SE England before spreading eastward into Belgium and the Netherlands, and later into western Germany. Kinematics and forcing could be even slightly better than earlier in the day and should support linear organization, while the presence of near 300 m2/s2 0-3 km storm-relative helicity suggests a potential for rotating updrafts. With these storms, a few tornadoes are possible, as well as some severe wind gusts and possibly some small hail.

Southern Adriatic, Ionean Sea and Greece...

Scattered thunderstorms are expected over the area in the range of the mid/upper low. It is not excluded that a waterspouts form with the storms, but otherwise the low CAPE and weak shear strongly limit the chance of severe weather.