Storm Forecast
Valid: Sat 23 May 2009 06:00 to Sun 24 May 2009 06:00 UTC
Issued: Fri 22 May 2009 19:15
Forecaster: DAHL
+ + + CORRECTED 22:32 + + +
A level 1 was issued for N Iberia into SW France mainly for large hail and severe wind gusts.
A level 1 was issued for the E Alpine region and N Slovenia mainly for large hail.
A level 1 was issued for extreme E Belarus, N-central Ukraine and extreme W Russia mainly for severe wind gusts and tornadoes.
SYNOPSIS
A high-amplitude Atlantic upper trough is in the process of closing off into a cut-off cyclone, which will establish over the Iberian peninsula. The residual trough will flatten out the upper ridge over the British Isles/North Sea and then disappear by Saturday evening. Downstream, another upper trough will travel across eastern Europe, reaching E Ukraine/central Black Sea towards the end of the period. At low levels, warm/moist air persists over the Mediterranean, being advected well into eastern Europe ahead of the E-European upper trough. The latter feature is accompanied by a SFC low pressure system while elsewhere rather quiescent synoptic surface conditions prevail.
DISCUSSION
... N Spain ...
It seems that ahead of the Iberian upper low, some potential for severe convective evolution exists. Indications are that high-based storms in an inverted-V type environment will be possible over eastern Iberia. Deep shear of 20 m/s will augment the negative-buoyancy driven downburst threat. In addition, high-based mesocyclones may develop, posing an additional threat for large hail.
... SW France ...
Further north towards France, influx of Mediterranean moisture should boost the CAPEs, but the presence of an Iberian EML will likely result in strong capping. In addition, deep shear seems have a minimum where the strongest thermodynamic fields are anticipated. However, shear is simulated to improve over southern France late in the day. Storms in this environment would pose the entire facet of severe weather, though the largest threats should be hail and severe wind gusts.
... E Alpine regions ... N Solvenia ...
The latest GFS simulates 20 to 25 m/s DLS over the E Alpine region, and in the presence of at least weak CAPE as well as QG/frontogenetic forcing for upward motion, scattered thunderstorms should develop. Kinematic fields suggest that isolated large hail may accompany the strongest storms.
... extreme E Belarus ... N-central Ukraine ... extreme W Russia ...
Another focus for severe evolution exists ahead of the E-European upper trough along and ahead of the attendant cold front. Though instability should be rather marginal, ample shear will be in place. LLS should exceed 12 m/s, and given weak capping, a couple of tornadoes may occur. However, strong forcing and minimal front-normal deep-layer flow components could result in a rather linear organization, so that the main threat may shift to severe wind gusts. Still, isolated cells ahead of the line will likely become mesocyclonic and pose a threat for tornadoes, as well as for large hail.
