Storm Forecast
Valid: Mon 04 Jul 2011 06:00 to Tue 05 Jul 2011 06:00 UTC
Issued: Mon 04 Jul 2011 06:46
Forecaster: DAHL

A LVL2 has been issued across the western Mediterranean primarily for large hail and damaging winds.

A LVL1 has been issued over east-central Europe mainly for marginally severe hail and wind gusts.

A LVL1 threat has been issued across western Russia mainly for excessive convective rainfall.

SYNOPSIS

The upper main frontal zone has shifted far southward into Mediterranean region, with an imbedded, de-amplifyingtrough moving into the central Mediterranean during the period. An extensive upper cut-off cyclone persists over the eastern parts of Europe. Both features are accompanied by weak SFC low-pressure areas, but overall, quiescent conditions prevail at the surface.

DISCUSSION

... western Mediterranean ...

Sunday's 12Z ascent from Murcia, Spain, exhibited very impressive lapse rates and rather deep moisture, resulting in 2000+ J/kg of MLCAPE ... indicating what the current air mass is capable of.

It seems that of MLCAPE of 1000 - 2000 J/kg, as well as a sturdy cap, will persist over the western Mediterranean on Monday. However, the lapse rates and instability may weaken some ... also, the depth of the moisture is uncertain, suggesting that MLCAPE might not be as high everywhere as in the Murcia sounding. However, ahead of the mid-level trough, sufficient large-scale ascent should exist to help initiate deep convection, although storm coverage remains quite uncertain given the strong cap. Also, it seems that a clear low-level focus for initiation is missing.

Deep shear in excess of 25 - 30 m/s should be sufficient for supercells and bow echoes, capable of (very) large hail and damaging winds. GFS assumes pockets of 10+ m/s LLS over the region, suggesting that perhaps a brief tornado could occur as well, though the chances seem somewhat limited given the strong cap. Although the anticipated low storm coverage will limit the overall magnitude of the severe threat, it also reduces the chances of destructive cell interference. It thus is possible that only a few but quite persistent/intense cells will develop. Moreover, if storms form and encounter pockets of deep moisture, upscale growth could occur, though this scenario is not explicitly simulated by either WRF or GFS. Still, the intense shear and at least locally ample instability requires a LVL2 threat, which is placed where shear looks to be most favorable and where models most coherently develop precip.

... east-central Europe ...

Scattered showers and thunderstorms should form across Poland into N Romania in a weakly unstable and weakly capped air mass. Deep shear is simulated to be in the 15-20 m/s range, which is within the overlap of the supercell and multicell parameter spaces. It seems that the most intense cells could produce some hail/wind briefly exceeding severe limits, marginally warranting a LVL1 threat.

... western Russia ...

Rather widespread storms are expected E of the eastern-European upper low in a rather moist and weakly-capped air mass. Deep shear should be rather weak with 5-10 m/s, so that the overall severe threat should be limited. However, favorable interactions of storms with previously laid-out outflow boundaries or similar mesoscale features may support a few very sporadic/brief large hail/severe wind events. The main threat should be excessive convective rain, though, given slow storm motions and anticipated large storm coverage.