Storm Forecast
Valid: Thu 03 Feb 2011 06:00 to Fri 04 Feb 2011 06:00 UTC
Issued: Wed 02 Feb 2011 20:52
Forecaster: GATZEN

SYNOPSIS

A deep trough is located near Greece and will slowly move eastwards on Thursday. To the north, a strong westerly jet expands across northern Europe.

DISCUSSION

Scotland, North Sea, and south-western Scandinavia

A region of interest will be north-western Europe. A strong westerly flow will affect this area on Thursday. Late in the period, another, very strong mid-level jet streak is forecast to reach more than 60 m/s at 500 hPa over the northern British Isles. A frontal wave will be located to the east of this jet streak and will rapidly move eastward. Current scenario is that the moist low-level air mass will be not overlap with the deep lift near the jet streak axis, where quite cold mid-levels are forecast to lead to CAPE. So only a shallow line of convection may develop along the cold front and only sporadic lightning is forecast if any. Nevertheless, this strongly forced line may produce severe wind gusts and tornadoes given a bulk shear up to 20 m/s in the lowest kilometre. An upgrade to level 1 may be needed when sufficient instability will develop along the cold front.

To the west of the cold front, severe synoptic winds are forecast with the sting jet of the low. Weak instability in the cold air mass will likely assist for some showers that may lead to a mixing of the high winds that will be about 45 m/s at 850 hPa to the ground.

Aegean and surroundings, south Mediterranean

Given the cold mid-level air masses near the trough center, steep lapse rates are present over the Mediterranean Sea, and with some low-level moisture especially east of a surface low pressure system, CAPE is forecast to develop.

One focus of convection will be the center of the surface low, where the boundary-layer moisture will reach up to 8 g/kg. The low-level convergence and weak warm air advection from the south-east will result in precipitation that can be quite intense. Embedded thunderstorms may develop that can contribute to an excessive rain threat over the Aegean region. The weak instability will limit the severe thunderstorm potential. But given a rather strong southerly flow to the east of the low that will result in more than 10 m/s bulk shear in the lowest kilometre, a tornado is not ruled out near the cold front.

Farther west, showers and thunderstorms are forecast near the base of the trough in a low-level cold air advection regime. These storms will likely be rather weak due to the weak vertical wind shear and forcing.