Storm Forecast
Valid: Thu 26 Dec 2013 06:00 to Fri 27 Dec 2013 06:00 UTC
Issued: Wed 25 Dec 2013 23:16
Forecaster: GATZEN

A level 1 was issued for the western and central Mediterranean mainly for severe wind gusts.

A level 1 was issued for parts of the Adriatic and Aegean mainly for tornadoes and severe wind gusts as well as excessive precipitation.

A level 1 was issued of western Norway mainly for severe wind gusts.

A level 1 was issued for northern Ireland and western Scotland mainly for severe wind gusts.

SYNOPSIS

East of new intense cyclogenesis across the northern Atlantic, the old storm's trough is pushed into Europe. The southern part will cut off over the Mediterranean whereas the northern portions will cross the North Sea. Eastern Europe is affected by a southerly flow.

While well-mixed maritime air masses enter western and central Europe, dry air is present over eastern Europe except for improving low-level moisture across the east Mediterranean.

DISCUSSION

Western and central Mediterranean

A sharp trough over western Europe forms a cut-off low over the west Mediterranean Sea. A deeply mixed maritime air mass is located near the base of the trough and CAPE is expected although low-level moisture is quite marginal.

Storm organization will be limited due to the weak vertical wind shear near the trough's base. However, near the coasts, vertical wind shear will be stronger, allowing for some bowing lines to form. These will enhance the wind potential that is rather high even without deep moist convection and a level 1 is issued.

Further east, a rather strong southerly jet affects the area ahead of the developing cut-off low. DCVA is expected to spread from the Adriatic region to the Aegean at the end of the forecast period. At low levels, warm air advection is forecast and some lift will result in improving lapse rates. In the boundary-layer, a moist southerly flow is forecast and some CAPE is possible in the warm air advection regime ahead of the cold front. Although instability is limited and stratiform precipitation is also likely over most of the region, some embedded storms are forecast to develop.

Especially near the coasts, low-level vertical wind shear will be rather strong with 10-20 m/s in the lowest kilometer. Therefore, mesocyclones are not ruled out and tornadoes or severe wind gusts may be possible. Front-parallel flow will also be associated with a potential of excessive convective precipitation. Together with the cold front, the threat will move from the Adriatic Sea in the noon and afternoon to the Aegean Sea in the night and morning hours.

Western Norway

Near the center of the weakening Atlantic storm, a vort-max will travel northward affecting western Scandinavia on Thursday morning. The deeply mixed maritime air mass will allow for some CAPE, and showers or thunderstorms are expected.

Strong vertical wind shear near the coasts of Norway is expected to support storm organization. Especially bowing lines are forecast to be associated with an increasing wind potential, and a level 1 is warranted. Storm potential decreases during the period and moves north.

Northern British Isles

A new storm will affect the northern British Isles late in the period. Along the cold front, rather stable conditions are expected, and severe thunderstorms are rather unlikely. The best potential of a few embedded thunderstorms exost across northern Irleland on Thursday evening. These storms, however, may be capable of producing severe wind gusts given the strong background wind field. Additionally, a tornado is not ruled out.

In the wake of the cold front, a well mixed maritime air mass will enter the northern British Isles. Especially near the base of the trough, thunderstorms are possible. Given strong low-level vertical wind shear, some bowing lines are forecast to enhance the wind potential and a level 1 is warranted.