Storm Forecast
Valid: Thu 24 Nov 2016 06:00 to Fri 25 Nov 2016 06:00 UTC
Issued: Thu 24 Nov 2016 00:22
Forecaster: GATZEN

A level 2 was issued for the Tyrrhenian and Ligurian Sea region mainly for excessive precipitation and to a lesser extent for tornadoes.

A level 1 was issued Italy and southern France mainly for excessive rain and isolated tornadoes.

Synopsis

A large cut-off low is located across the Iberian Peninsula. A southerly flow affects the west Mediterranean ahead of it, and an embedded vort-max travels north during the period. Together with a moist south-easterly low-level flow, intense precipitation can be expected especially from the Tyrrhenian Sea region to the Ligurian Sea region. Behind a cold front, drier low-level air masses will spread into the regions further west what reduces the threat of excessive rain.

A ridge extends from the central Mediterranean to central Europe and the British Isles. Although lapse rates are quite steep to the north of the Alps, low-level cooling of the Föhn air takes place, so that no storms are expected. A cut-off low affecting western Turkey will also not be associated with storms due to a dry polar air mass that has entered the region earlier this week. Over northern Europe, intense polar trough is pushed into north-western Russia ahead of a ridge that expands into Scandinavia. Steep lapse rates near the center of the polar trough overlap with some Atlantic moisture over western Norway at the start of the period, where some thunderstorms can form along the western mountains of Norway.

DISCUSSION

Tyrrhenian and Ligurian Sea region

Ahead of the approaching cold front, moist low-level south-easterly flow continues. Parallel stratiform MCSs are expected along south-north orientated cold front. CAPE around 500 J/kg can be estimated given overlap with steep lapse rates from the west and stretching as the mid-level vort-max crosses the area. Excessive rain is quite likely again. CAPE will be weaker in the northern portions where low-level moisture is more limited. Therefore, precipitation can be stratiform in the Ligurian Sea region instead of convective.

Furthermore, tornadoes are not ruled out given strong low-level vertical wind shear.

Late in the period, threat weakens from the west as the cold front approaches, replacing the moist boundary layer.