Storm Forecast
Valid: Wed 10 Aug 2011 06:00 to Thu 11 Aug 2011 06:00 UTC
Issued: Wed 10 Aug 2011 07:42
Forecaster: PUCIK

A level 1 was issued for Northern Greece, Buglaria and Romania mainly for excessive precipitation, large hail and marginally severe wind gusts.

SYNOPSIS

At midlevels of troposphere, a complex of troughs is forecast over Europe, with the most significant one moving across Southeastern Europe, with up to 30 m/s jet-stream at 500 hPa surrounding its base. The trough is forecast to fill in and slightly de-amplify as it moves eastwards. Another trough will move from Scandinavia towards the Baltics during the day, associated with the strong zonal flow at its southern flank. The last short-wave trough is expected to influence Great Britain during the evening hours.

Closer to the surface, a low dominates over parts of Northeastern Europe, Turkey and also over Great Britain and its surroundings. Towards the south, a ridge emanating from the Azorian high stretches into Western and Southwestern Europe and also southern parts of Central Europe. The main frontal boundary lies momentarily across Eastern Europe, being strongly meridional, and stretching all the way from Southeatern Mediterranean into Northern Russia.

DISCUSSION

... Northern Greece, Bulgaria, Romania ...

An aforementioned trough is expected to provide a strong, concentrated zone of forcing, as suggested by IPV and Q-vector fields for this region, especially towards late afternoon and evening hours as the axis of the trough moves eastward. Forcing will likely result from DCVA and divergence in the left exit region of jet-stream. Both GFS and ECMWF do simulate low to moderate degree of instability, but values should not greatly exceed 1000 J/kg in terms of MLCAPE. Strong wind shear is forecast thanks to the strenghtening flow aloft, with more than 20 m/s of bulk shear in the 0-6 km layer. Moreover, slightly backed surface flow ahead of the frontal boundary will likely contribute to some marginal SREH values. Current thinking is, that, storms will be strongly tied to the frontal boundary and with parallel flow to it, especially concerning the northern extents of the Level 1, cell clustering into one or more MCS will be very likely. Nevertheless, especially in the first stages of scenario and over southern parts of Level 1, isolated strong multicellular and supercellular convection is also possible.

In case that strong multi and supercells form, large hail and marginally severe wind gusts might be observed, especially in the beggining stages of the scenario. Later on, the nature of threat will likely shift into the excessive precipitation as several rounds of storms will travel northeastwards along the frontal boundary, possibly inducing training pattern in very moist environment as revealed by Effective PW values. The excessive precipitation threat will be the greatest for the northern and eastern extents of Level 1.

... Southern Spain ...

In the environment of moderate CAPE and wind shear and dry boundary layer, conditions would be conducive to strong multicells capable of large hail and possibly some isolated downbursts. However, initiation seems to be very unlikely at the moment due to the very high CIN values. This area will be monitored for the hints for initiation and a possible update to Level 1.