Storm Forecast
Valid: Mon 28 May 2007 06:00 to Tue 29 May 2007 06:00 UTC
Issued: Sun 27 May 2007 23:09
Forecaster: GROENEMEIJER
SYNOPSIS
A large low-pressure area over France moves eastward. Cold air is advected into Europe SW of a frontal system initally over Germany. Warm air is advected far to the west on the south side of a warm front over Denmark, the Baltic Sea, S Finland and N Russia. A weak mid-level trough moves eastward from the Ionean Sea and reaches W Turkey on Tuesday morning.
DISCUSSION
S Finland, Russia...
A warm front is expected to stall along a line from southwestern Finland over Lake Onega eastward. High values of helicity (200-300 m2/s2) and 0-6 km bulk shear of near 20 m/s are expected near the front. Models agree on the development of convection in this environment possibly capable of sustaining supercells. Hence a number of rotating/supercell storms are expected in addition to more poorly organized storms. Given that LCL's will be low, the supercells have a risk of producing tornadoes. The amount of shear does appear a little modest overall and the detailed evolution cannot be forecast in this time frame so that we will not issue a level 2 for any area at this moment, but this may be done in an update later.
Some large hail and strong winds are possible too, with the strongest winds most likely with bowing storm systems moving eastward along the frontal zone in the Russian part of the level 1 area.
The severe storm threat should slowly subside during the late evening and night.
N and central Germany...
Between a warm front over Denmark and southern Sweden and a cold front from NW Germany to Austria, warm air should flow eastward and rise while doing so. Models agree on the development of a large MCS over Central or N-Central Germany during the day that should move Nward. The environment in which the storms will form is one of surface-based instability, near 15 m/s 0-6 km shear, some SRH (~ 200 m2/s2) and low LCL heights. This is a setup marginally favourable for the development of tornadoes especially with storms that remain more or less isolated for soem time. CAPE should be sufficient for a number of large hail reports. The MCS is expected to be of the back-building rather than the bowing type, so that wind threat should remain relatively limited. If shear improves in newer model runs an upgrade to level 2 may be issued. It seems that the MCS should continue well into the night affecting parts of the North Sea and perhaps southern Denmark.
S Germany, Czechia...
About 500-1000 J/kg MLCAPE is expected to form ahead of the eastward moving cold front over southern Germany. With 15-20 m/s 0-6 km shear available this should be an environment capable of sustaining strong multicells and perhaps a supercell. These storms should have a main threat of large hail and strong, locally severe wind gusts.
Albania, F.Y.R. of Macedonia, Greece, W Turkey...
Storms are expected to be ongoing over Albania and Wrn Greece at the beginning of the period. Elsewhere, capping should be a major limiting factor despite the otherwise favourable setup for severe storm development. MLCAPE should be in the 500-1000 J/kg range and deep-layer shear more than sufficient for supercells and strong bow echoes. Strong forcing however is lacking.
Nevertheless expect scattered storms, possibly developing into the aformentioned supercells and bowing systems, and capable of producing large hail and especially strong winds to affect the indicated level 1 area. The focal point of storm activity should move from west to east through the area through the day.
