Storm Forecast
Valid: Thu 01 Nov 2012 06:00 to Fri 02 Nov 2012 06:00 UTC
Issued: Wed 31 Oct 2012 22:12
Forecaster: GATZEN

A level 2 was issued for the northern Aegean mainly for excessive precipitation.

A level 1 was issued for the central and southern Adriatic, the Aegean, and surroundings mainly for excessive precipitation, severe wind gusts, tornadoes and large hail.

A level 1 was issued for

SYNOPSIS

Two intense troughs will affect Europe. The first actually present over the north Mediterranean will move north-eastwards into eastern Europe, while its trough axis crosses the east Mediterranean. From the north-west, a second intense trough will move into Europe. Its axis will cross France on Thursday.

Discussion

Adriatic and Aegean

A cold front will move eastwards across the Adriatic and the Aegean Sea during the period. Ahead and along the cold front, southerly low-level flow will advect rich moisture into the Adriatic and Aegean Sea.

At higher levels, models indicate a ridge of warm air spreading eastwards ahead of the trough axis. This air mass is characterized by steep lapse rates and models indicate increasing CAPE from the southern Adriatic Sea to the Aegean Sea.

A capping inversion will likely limit convective initiation in the southern portions of the Mediterraneran, whereas strong low-level convergence and upslope flow is forecast to lead to thunderstorms along the coasts and across the Aegean Sea.

Further north, uncapped instability is expected given the advection of moist-adiabatic lapse rates from the west, low-level moisture increase and further QG forcing. Thunderstorms are therefore forecast across the central Adriatic and surroundings as well.

Storms across the Aegean will develop in an favorably sheared environment with 15 to 20 m/s deep layer bulk shear and 10 m/s 0-1 km vertical wind shear. Given rather low LCL heights and strong low-level shear, tornadoes are forecast. Supercells or multicells may also produce large hail and severe wind gusts. Across the Adriatic, vertical wind shear is weaker, but a few wind events or a tornado are also not ruled out.

The main threat, however, is excessive precipitation along the coasts, although the cold front will move gradually eastward. This will be associated with decreasing thermodynamic profiles from the west, and severe potential will decrease.

Northern France, the Benelux countries, and surroundings

An intense polar trough will spread into western Europe from the north-west. A trough axis will cross northern France rapidly during noon and tilts negatively across the Benelux countries. Strong QG forcing is expected.

Latest models indicate rather steep lapse rates spreading eastwards with the trough. At low levels, moisture from the Bay of Biscay will advect into northern France and the Benelux countries during the day. Some diurnal heating will likely result in instability in the noon and afternoon hours.

Given the strong vertical wind shear that exceeds 20 m/s DLS and 10 m/s LLS across northern France and the Benelux countries, well organized multicells and mesocyclones are forecast. These rapidly moving storms may be capable of producing severe wind gusts. Additionally, tornadoes are not ruled out especially across the Benelux countries and surroundings. Briefly large hail may also occur with stronger storms.

Main limiting factor is the weak instability and additionally relatively weak low-level convergence along the trough axis. This may lead to weaker showers especially in the southern parts of the area. A low-end level 1 is issued. After sunset, low-level cooling is expected to limit convective potential significantly.