Storm Forecast
Valid: Mon 14 May 2012 06:00 to Tue 15 May 2012 06:00 UTC
Issued: Mon 14 May 2012 04:29
Forecaster: PUCIK

A level 1 was issued for Spain mainly for large hail and severe wind gusts.

A level 1 was issued for SW Italy mainly for excessive precipitation.

A level 1 was issued for the Ionian Sea, Greece, Macedonia, Aegean Sea, S Bulgaria and W Turkey mainly for excessive precipitation and to the lesser degree for marginally large hail and tornadoes

A level 2 was issued for NW and N coastline of the Aegean Sea mainly for excessive precipitation and to the lesser degree for tornadoes and marginally large hail.

SYNOPSIS

Two major synoptic scale features will dominate the mid and upper levels of troposphere over the forecast area - the first one being a deep cyclonic vortex over the Norwegian Sea with an attendant trough crossing British Isles during the afternoon hours and amplifying towards southeast. The second one will be a rapidly translating trough moving from Italy towards Greece and then Turkey. Strong 30 m/s flow is forecast at the base of the trough. An ill defined ridge will develop between these two features while a de-amplification of ridge over Iberia is forecast.

Closer to the surface, two low pressure centers are simulated - one centered over the Norwegian Sea with very little movement during the day and central pressure close to 970 hPa, another one associated with the trough over the Mediterrranean, forecast to slightly deepen over the Aegean Sea in the night hours. A ridge over Central Europe will connect a large high over the Atlantic with high pressure system over northern half of Eastern Europe. Main frontal boundary will run from Northern Iberia to Southern Italy, Balkans, curving towards Eastern Ukraine and Russia.


DISCUSSION

... Spain ...

A very difficult forecast for Spain with borderline Level 0/1 situation as convective initiation remains very questionable. Models are in major disagreement regarding the degree of instability and convective precipitation as GFS produces most of instability over the Central Spain, while ECMWF along the coasts and Pyrennees. Still, northern half of Iberia will be under strong mid-level flow, yielding DLS values easily over 20 m/s with enhanced SREH along the coastlines. An isolated strong multicell or supercell capable of large hail or severe wind gusts is possible once DMC initiates. A low end Level 1 is issued attm, albeit a downgrade might become necessary during the day if inititation will become less probable.

... South Italy, Southeastern Europe ...

An active pattern is forecast over the area especially thanks to the approach of the sharp trough with favorably located jet-streak. Its exit region at the forward flank of the trough constitutes strong synoptic scale forcing that will quickly translate over the region especially in the evening to night/morning hours regarding the Balkans and Aegean Sea part. Southerly winds ahead of the surface low will advect moist airmass towards north with dewpoints over 16° and mixing ratios approaching 12 g/kg. Moderate instability is forecast by most of NWP, with MLCAPE values over the Ionian and Aegean Sea mostly between 500 - 1500 J/kg. Strengthening wind field ahead of the trough will increase the vertical wind shear, which should exceed 20 m/s in the 0-6 km layer, especially in the southern sector of Level 1. Further to the north, mostly moderate wind shear is forecast. Close to the coastline, models agree on enhanced SREH values and also slight increase in the LLS, which can locally exceed 10 m/s, especially in the Level 2. A low level jet is forecast over the Aegean Sea, reaching 15-20 m/s at 850 hPa level as the suface low should deepen thanks to the strong focing.

The main threat forecast for this region will very likely be an excessive precipitation. Numerous MCS with training pattern are well possible and with very moist airmass, almost saturated at low to mid levels, low LCLs and moderate mixing ratios, precipitation intensities might be quite high. The highest chance for excessive precip will exist over the northern coastline of the Aegean Sea, where a LLJ will impinge on the coastline areas. Elsewhere, marginally large hail might occur with stronger cells, mainly in the southern half of Level 1, where strong DLS is forecast, increasing the chances for supercellular development.
A tornado is not ruled out either, albeit LLS should be only locally enhanced along the coastlines.