Storm Forecast
Valid: Wed 11 Aug 2010 06:00 to Thu 12 Aug 2010 06:00 UTC
Issued: Tue 10 Aug 2010 22:30
Forecaster: PUCIK

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

A level 1 was issued for a belt from Romania to Northern Russia mainly for large hail and to the lesser extent for severe wind gusts.

SYNOPSIS

Dominant macrosynoptic feature at midlevels will be a cyclonic vortex centered over the Northern Sea by Wednesday 12 UTC, surrounded by flow exceeding 20 m/s at 500 hPa. To the east, a ridge covers most of Eastern Europe and especially Russia, where unseasonably hot airmass has settled. Between these two features weak southwesterly flow will be observed.

Closer to the surface, a shallow low will stretch from the Nothern Sea towards Scandinavia and a ridge of high pressure will cover most of Central and Eastern Europe. Two frontal systems will become foci for thunderstorm development during the day. The first cold front will move across Western Germany and France during the day while the second will stall over Western Russia.

DISCUSSION

... Eastern Spain ...

A plume of hot airmass, characterized by high lapse rates, apparently an elevated mixed layer from the Atlas mountains will cover most of the Iberian penninsula. With thermally induced shallow low over the land, easterly winds will advect moister airmass over this region, generating moderate latent instability, with MLCAPE values forecast well over 1000 J/kg by GFS, ECMWF and WRF model. With moderate values of DLS, reaching 15 - 20 m/s and enhanced SREH values induced by easterly surface winds, conditions seem to be quite favorable to well organised convection, including a possibility of supercells.

Due to the hot airmass at lower levels of troposphere, significant values of CIN are predicted and models are breaking out only very spotty and small amounts of precipitation. With lack of synoptic scale lift, CIN values will probably remain high and mesoscale lift from the local convergence zones and/or forced ascent due to the topographic barriers. Despite the uncertainity regarding storm initiation, low end Level 1 is issued for the region as thunderstorm coverage might prove more plentiful than expected and with well organised storms, threat of large hail or severe wind gusts will exist.


... Romania ...

GFS and ECMWF models are quite optimistic regarding CAPE values, which might exceed locally 1500 J/kg thanks to the diurnal heating and the moisture convergence ahead of the front. In such configuration, even in weak wind field and DLS around 10 m/s, isolated pulse storms are not ruled out with threat of downbursts or marginally large hail.

... Level 1 in Ukraine, Russia ...

Moderate instability is predicted by GFS and ECMWF model with wind shear values increasing towards north, where up to 20 m/s of DLS is simulated. Surface convergence ahead of the cold front will initiate the storms and an ageostrophic component of the flow will enhance SREH values. Initiation will be more plentiful especially towards the evening hours as mostly the result of mesoscale processes, with the lack of synoptic scale forcing. Well organised multicells are possible and a brief supercell is not ruled out either in such conditions. Stronger cells might be capable of large hail and/or severe wind gusts.