Storm Forecast
Valid: Mon 29 May 2006 06:00 to Tue 30 May 2006 06:00 UTC
Issued: Sun 28 May 2006 21:09
Forecaster: GROENEMEIJER

SYNOPSIS

Monday at 06:00 UTC... a very broad longwave trough is located over Europe. The axis of a jet around the base of the trough - which roughly coincides with a baroclinic zone - is located from Scotland to the Alps to the northern Balkans to the eastern Ukraine. A rather intense shortwave trough, coupled with a cold bubble at mid-levels is expected over southern Scotland and reaches northern Switzerland on Tuesday morning.

DISCUSSION

Northern Italy, northwestern Balkans...

A frontal zone is expected initially along a line from Northeastern Italy to Belgrade to southern Moldova. The approach of the aforementioned trough is expected to induce cyclogenesis at the leeward side of the Alps over northeastern Italy.

Some instability, around 500-1000 J/kg of SBCAPE is expected to form over the Ern Po Valley, NErn Italy and Wrn Slovenia. This occurs especially when upward motion increases in response to the approaching trough.... and an easterly breeze into the Po-Valley becomes stronger, advecting moist air inland.

Convective initiation is expected to occur in the second half of the afternoon and during the evening across the level 1 area. Strong (around 30 m/s 0-6 km bulk) shear is expected over the area and storm-relative helicity for a right-moving storm will likely be on the order of 200-250 m2/s2. As a result, initiating storms can easily develop rotating updrafts. Thus, appears that the threat of large hail will considerable.

Because low-level (0-1 km bulk) shear should locally be in excess of 10 m/s and LCL height will not be large, there appears to be a threat for tornadoes as well. Because of the somewhat limited instability, however, present thinking is that the overall threat does not warrant a higher risk level than level 1.

Ern Bulgaria, SErn Romania...

Further east along the frontal zone, low amounts of instability are expected to form over Ern Bulgaria and SErn Romania. Some storms may form as a result... although only part of the numerical models predict convective initiation. The presence of a rather helical and moderately sheared environment, suggest that the formation of one or two supercell storms may occur. In that case, some (possibly large) hail and wind gusts will likely result.

British Isles, France, Benelux, western Germany...

As the aforementioned trough moves southward across these areas, clustered storms and small squall-lines are expected. It is not ruled out that a couple of briefly rotating updrafts form as well, yielding an enhanced threat of large hail. The absence of strong low-level shear suggest that the chance of tornadoes will be relatively small.

Southern Scandinavia...

Strong insolation of a potentially unstable air-mass will likely result in scattered to widespread storms over Srn Norway, Denmark and Srn Sweden. Small hail and, given moderately low LCL heights and weak winds, one or two weak tornadoes may occur as a result.

Spain...

Not unlike Sunday, scattered storms are expected to form at the end of the afternoon. Given that lapse rates are steep, a few strong gusts can be expected with the storms, especially over NErn Spain where somewhat stronger low-level winds are forecast.