Storm Forecast
Valid: Tue 08 Jun 2010 06:00 to Wed 09 Jun 2010 06:00 UTC
Issued: Mon 07 Jun 2010 21:08
Forecaster: KOROSEC

A level 1 was issued for NW Russia mainly for severe wind gusts and lesser extent for tornadoes and large hail.

A level 1 was issued for Czech Republic, SE Germany and N Austria mainly for large hail and strong wind gusts.

A level 1 was issued for east-central France mainly for marginally large hail and a brief tornado.

SYNOPSIS

Weak geopetential heights are placed over much of Europe while a large trough over western Europe slowly shifts southwards and transforms into an upper low towards the Wednesday morning. Another short-wave trough continues eastwards from Baltic states into NW Russia.
At surface, a frontal boundary extends from NW Russia into central Europe where it advects northwards as a warm front during the second half of the period. Another front extends from the large surface low over UK SW-wards across central France into Iberian peninsula. The third front races onto western Iberia overnight when the upper low/new system approaches.

DISCUSSION

... Czech Republic, SE Germany and N Austria ...

Placed beneath the weak upper ridge over central Europe/Balkans, weak wind field will be in place. Near surface mixing ratios of around 12 g/kg south of the weak/quasi-stationary surface front should result in moderately strong instability with MLCAPEs locally exceeding 1500 J/kg. Expect mostly diurnal driven storms, where some of them could bring threat for large hail and strong wind gusts. Locally, rather slow moving storms can lead into some flash flood risk.

... east-central France ...

The convective activity will be mostly aligned to the frontal zone and areas ahead of it once the diurnal heating takes place. Pre-frontal initiation is more likely over the Massif central. Given the marginal instability overlaping with 10-15m/s 0-6km shear, mostly multicells are likely. Storms may tend to cluster into a larger system. In the late afternoon/early evening hours, when the upper trough approaches northern Iberia, a weak surface low forms over NE Spain and an increasing LL jet results in enhanced shear in the lowest levels across the level 1 area. More backed wind field leads into several hundreds of m^2/s^2 of SREH3 as well, rising the potential for more organized severe storms. Given the near 20 m/s of deep-layer shear, a couple of more isolated supercells with threat for large hail and weak tornado could result.

... NW Russia ...

Ahead of an eastwards moving short wave trough, warm and ustable airmass advects NE-wards behind the warm front. Rather strong deep-layer shear around 25 m/s and MLCAPE near 500-1000 J/kg spreaded across the warm sector should created environment for some severe storms. A maintaining cluster of storms is possible along the leading cold front with a few embedded supercells. Posing a threat for mostly severe gusts and marginally large hail. With at least 10 m/s of LL shear and rather low LCL heights, a tornado threat is not ruled out either.

... western Iberia ...

Weak to moderate instability builds up ahead of an approaching surface front coming onto western Iberia towards the evening hours. With moderate mid-level jet streak and deep-layer shear near 15-20m/s in place, a few organized severe storms could occur over Portugal. But rather limited threat and coverage preclude any threat levels attm. However, a marginally large hail and strong wind gusts threat exist with the strongest storms.