Storm Forecast
Valid: Thu 12 Jun 2008 06:00 to Fri 13 Jun 2008 06:00 UTC
Issued: Wed 11 Jun 2008 22:53
Forecaster: DAHL

SYNOPSIS

Deep upper trough is present over N Europe, exhibiting several partly amplifying perturbations at its periphery -- one of which is a cut-off cyclone over the N Mediterranean which will merge with the mean trough during the period -- which results in an overall expansion of the upper trough ... which will cover most of Europe at the end of the forecast period. Aligned roughly parallel to the upper frontal zone at the S and W periphery of this upper trough, is a rather intense quasi-stationary low-level baroclinic zone, stretching from the N Iberian peninsula across the Alps northeastwards into central Russia. A rather extensive SFC low will persist over Scandinavia, NE Europe, and NW Russia, but otherwise rather quiescent conditions should continue over Europe. South of the low-level frontal zone, weakly, and at places moderately unstable air is present.

DISCUSSION

... N Balkans ...

It seems that the air mass over the N Balkans will have undergone little changes compared to Wednesday, so that moderately strong thermodynamic fields with MLCAPEs in the 1000 to 1500 J/kg range are expected. Despite rather high LCLs near the top of a rather deep CBL, previous similar situations have resulted in non-mesocyclonic tornadoes, which may be due in part to the rather deep layer of steep lapse rates, as well as to vanishing capping. The threat appears to be too low for a categorical risk, but a few events may well occur. In addition, brief marginally severe hail may occur despite minimal shear, as cells may cluster and provide their growing neighbors with hailstone embryos. The severe weather threat should be too low for a categorical risk, however.

... Sicily ...

There will be a small region stretching from S Italy into S Greece, where 15 to 20 m/s DLS will exist along with positive CAPE, providing a rather favorable environment for severe evolution. Forcing for upward motion will be provided by the N Mediterranean upper low which will merge with the digging N European long-wave trough in the evening hours. GFS is somewhat reluctant to develop strong QPF signals, but indications are that the forcing will exist W of the thermal-ridge axis at 850 hPa, suggesting that the capping may be reduced when/where large-scale upward motion occurs. Different mesoscale models as well as the GFS suggest that highest probabilities for convective initiation will exist over Sicily. Given the possibility of organized multicells as well as mesocyclones, large hail along with severe wind gusts may occur. Despite the uncertainty with respect to whether or not convection develops, a level one threat seems to be warranted.

... N France ...

Scattered thunderstorms will likely develop over France in weakly unstable thermodynamic environment along and in the wake of a weak occluded frontal system associated with an upper vort max. DLS of 20 m/s along with 7 to 10 m/s 0-1 km shear will likely exist. Expect a few marginally severe hail/wind events, and possibly also a brief tornado or two. Though thermodynamic support should be quite weak, moderately strong forcing for upward motion as well as rather decent shear justify the introduction of a level-one risk area.

... Baltic States ...

Rather shallow diurnally-driven convection is anticipated to develop over NE Europe, the Baltic States, and NW Russia. Over the Baltics, sufficiently strong shear will be in place to support an isolated marginally severe hail/wind event as well as a brief tornado or two. However, marginal nature of allover kinematic/thermodynamic setup precludes a categorical risk at the moment.


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