Storm Forecast
Valid: Mon 23 May 2011 06:00 to Tue 24 May 2011 06:00 UTC
Issued: Mon 23 May 2011 14:35
Forecaster: DAHL

A level one threat has been issued across the eastern Baltic States, northern Belarus, and extreme NW Russia mainly
for marginally severe wind gusts/hail and brief tornadoes.


*WE APOLOGIZE FOR THE LATE ISSUANCE OF THE FORECAST CAUSED BY TECHNICAL ISSUES*


SYNOPSIS

A meandering and rather compact upper zonal jet stream is stretching across the N Atlantic and the northern portions of Europe into NW Russia. The imbedded short-wave trough (and its attendant cold front) analyzed over the North Sea on
Sunday evening will continue lifting northeastwards while attaing an increasingly negative tilt ... reaching the Baltic States/NW Russia late in the period before it eventually closes off into a small cut-off cyclone. Upstream ... the next Atlantic trough will cross the British Isles and reach western continental Europe by early Tuesday morning. Elsewhere, synoptically-quiescent conditions are prevailing.

DISCUSSION

... eastern Baltic States ... N Belarus ... extreme NW Russia ...

Some 500 to perhaps 1000 J/kg of MLCAPE should prevail in the airmass east of the cold front. Though the deep-layer shear
is diminishing towards the east into the warm sector, some 10 to 15 m/s DLS should exist along the cold front. The northern
extension of the warm sector air should in addition experience low-level shear of order 10 m/s. This setup should be marginally supportive of multicellular storms, some of which may briefly attain rotation. Although the primary severe threat will be marginally severe winds/hail, a brief tornado or two cannot be discounted.

... northern Iberia ...

Mainly diurnally/orographically driven storms should develop over the northern parts of Iberia. Though CAPE and shear
should be quite meager, rather dry sub-cloud layers suggest that strong outflow winds may occur. The severe threat
is too small for a LVL1 area, though.

... S France ... inter-Alpine regions ... N Italy ... eastern parts of Europe ...

It seems that widespread diurnally driven storms will occur in a weakly capped 500-1000 J/kg MLCAPE environment. Shear profiles will be quite weak, so that no organized severe threat is anticipated. However ... there always exists the chance of local augmentations of the large-scale environments e.g., by outflow boundaries, boundary-layer rolls, or orography. Hence, chances for very sporadic severe events (including the entire facet of severe weather) are nonzero. Moreover, local flooding may occur given the slow storm motions. However, it is impossible to highlight a certain area, and the overall threat is too low to warrant a LVL1 threat area.