Storm Forecast
Valid: Thu 20 Nov 2014 06:00 to Fri 21 Nov 2014 06:00 UTC
Issued: Wed 19 Nov 2014 23:31
Forecaster: GATZEN

A level 1 was issued for the south-western Turkish coast mainly for excessive precipitation and to a lesser extend large hail and tornadoes.

A level 1 was issued for western Portugal mainly for excessive precipitation and to a lesser extend large hail and tornadoes.

SYNOPSIS / DISCUSSION

The European trough digs south-east and starts to form a cut-off across south-western Europe. Ahead of the cold front, a tongue of moist air becomes unstable due to steepening lapse rates, affecting the south-western Turkish area. Back-building storms along the cold front will pose a threat of excessive precipitation especially where upslope flow will assist the development of stronger storms. Vertical wind shear about 15 to 20 m/s in the lowest 6 km will also allow for a few well-organized storms capable of producing isolated large hail and tornadoes. The threat spreads east during the day as the cold front moves on.

Dry and cool air masses spread into the Mediterranean in the wake of the trough. Better moisture is present across the western Mediterranean, but ridging and the advection of elevated warm air leads to a strong capping inversion.

The only exception is the coast of Portugal. Ahead of an amplified Atlantic trough, a strong southerly low-level jet advects moist air into the region. Steep lapse rates spreading west from the Iberian Peninsula will overlap with the moist maritime air mass, allowing for CAPE in the order of 600-1000 J/kg. Within the axis of moist air, models agree on thunderstorms near the coasts along the land-sea-breeze convergence in an area of low-level warm air advection from the south-west.

Storms that form can quickly organize due to strong vertical wind shear exceeding 15 m/s in the lowest 3 km. Excessive rain due to line-parallel storm motion is not excluded, as well as large hail that is most likely in the southern part of the risk area. Additionally, tornadoes are not ruled out, although the low-level buoyancy is limited. Convective activity will spread west late in the period due to increasing easterly winds and a strengthening capping inversion from the east.