Storm Forecast
Valid: Thu 13 Nov 2014 06:00 to Fri 14 Nov 2014 06:00 UTC
Issued: Thu 13 Nov 2014 00:53
Forecaster: GATZEN

A level 1 is issued for Greece, the Aegean, and western Turkey region mainly for excessive precipitation and to a lesser extend waterspouts.

A level 1 was issued for Portugal and north-western Spain mainly for excessive precipitation and to a lesser extend tornadoes.

SYNOPSIS

A new intense north-Atlantic trough forms to the west of Europe. Downstream, ridging leads to an amplification of the European high. This is associated with a disappearing west-European trough that ends as a cut-off process across the Mediterranean. This cut-off will move to the Aegean Sea late in the period.

Greece and Aegean region, western Turkey

A southerly low-level flow has evolved across the Aegean Sea region as indicated by latest observations. A mixing ratio of more than 10 g/kg as indicated by latest GFS model is expected to be realistic in the morning hours. Rather steep 800 to 600 hPa lapse rates sampled by latest ASDE0211 sounding are forecast to advect east and will partly overlap with the rich moisture, resulting in some 100s J/kg CAPE. Main focus for initiation will be low-level convergence ahead of the approaching cut-off low due to QG lift, but upslope flow will also support persistent storms forming in the warm southerly flow regime.

Main severe threat will be excessive precipitation given the moist air mass and persistent deep moist convection. With weak vertical wind shear, degree of organization is low and other hazards are not forecast despite water spouts that can form especially late in the period below the cut-off centre.

Tyrrhenian to Adriatic and Ionian Sea region

The passage of the cut-off centre will be associated with strong showers and thunderstorms that may be accompanied by excessive precipitation locally. Waterspouts are forecast given some low-level CAPE overlapping with weak vertical wind shear. The threat of severe convective weather decreases later in the period.

Portugal, north-western Spain, Bay of Biscay region

Ahead of the approaching new Atlantic trough, a strong south-westerly low-level jet transports a tongue of very moist air spreads northward affecting the western Iberian Peninsula and the Bay of Biscay region. Parallel to the flow, precipitation bands with embedded convection are indicated by latest models. These can lead to excessive precipitation. Additionally, strong low-level vertical wind shear is forecast, and tornadoes are not ruled out near the coasts. Main focus will be southern Portugal with the best overlap of low-level CAPE and shear, but isolated events are not ruled out further north up to the Bay of Biscay. During the night, the cold front will cross the area leading to decreasing convective activity.