Storm Forecast
Valid: Sun 10 Jan 2010 08:00 to Mon 11 Jan 2010 06:00 UTC
Issued: Sun 10 Jan 2010 08:26
Forecaster: SCHLENCZEK

A level 1 was issued for NW Morocco, SW Portugal and S Spain mainly for excessive precipitation and severe wind gusts and to a lesser extent for tornadoes.

A level 1 was issued for NW Greece, Albania and W Serbia-Montenegro mainly for excessive precipitation.

A level 1 was issued for the Bosporus region and W Black Sea region mainly for severe wind gusts.

A level 1 was issued for W Turkey mainly for severe wind gusts and to a lesser extent for tornadoes.

SYNOPSIS

Cold air has overspread most parts of Europe and deep moist convection should be confined to two low pressure systems over the Mediterranean. The 1005 hPa surface low over northern Italy will move towards the Black Sea during the period. Thunderstorms are most likely near the upper cold core of this system where shear and forcing are quite marginal. As the associated upper trough reaches W Turkey, a tongue of unstable air should be located under the left exit of a 60 m/s upper jet streak which stretches from the Tyrrhenian Sea and S Greece towards the Bosporus region.

Another low pressure system, initially located near the Azores, moves eastward towards SW Iberia / Strait of Gibraltar while occluding. This system may produce heavy rainfall in parts of SW Portugal / S Spain. A large area of stratiform precipitation ahead of the trough is moving onshore, followed by isolated or clustered thunderstorms. Most of the precipitation is forecast between Sunday 12 UTC and Monday 06 UTC.

DISCUSSION

...W Greece, Albania, W Serbia-Montenegro...

After the heavy precipitation event on Saturday, some more 20 - 30 mm rain are expected to fall in the first half of the forecast period. Although numerous storms will move onshore, it is questionable whether our excessive precipitation criterion will be fulfilled in this period. A level 1 was issued as a continuation of this heavy precipitation event will likely cause widespread flooding. Besides an isolated waterspout over the Adriatic / N Ionian Sea, other types of severe weather are not expected to occur as both shear and CAPE are considerably low.

...W Turkey, Bosporus region, E Bulgaria, E Romania...

A cold front that stretches from W Ukraine via central Romania, eastern Greece and Crete towards Libya will move eastward. Directly along the cold front, MLCAPEs in order of 200 - 400 J/kg are expected to form and around midday, deep layer shear and forcing will increase in this region. As the low level winds are quite strong (20 - 25 m/s at 850 hPa), severe wind gusts may occur with the strongest storms and a level 1 was issued for the region where the wind gust threat is augmented. Very intense deep layer shear (35 - 40 m/s) and LLS in order of 15 m/s over SW Turkey may allow an isolated tornado as well. The expected accumulated precipitation sums will likely be sub-severe.

...Strait of Gibraltar, NW Morocco, S Spain, SW Portugal...

Ahead of an approaching upper trough, moderately warm and unstable air is advected towards NW Morocco and SW Iberia. Over Iberia, deep layer shear will likely stay below 20 m/s but MLCAPEs in order of 500 - 800 J/kg should be sufficient for some organised multicells which will move onshore after 12 UTC. Near the coastlines, LL shear is augmented and a tornado may occur. Some of the storms may also profit from a strong wind field at lower levels and could produce severe wind gusts. Besides the tornado / severe wind gust threat, excessive rainfall and flooding is possible where storms persist for a long time. As the unstable airmass is advected eastward into the W Mediterranean, thunderstorm activity will decrease after midnight.