Forecast Update
Valid: Mon 29 Jul 2013 13:00 to Tue 30 Jul 2013 06:00 UTC
Issued: Mon 29 Jul 2013 13:47
Forecaster: PUCIK / GROENEMEIJER

A level 3 was issued for Northern Italy mainly for large to very large hail, severe to extremely severe wind gusts, tornadoes and to the lesser extent for excessive precipitation.

A level 3 was issued for Northern Austria towards the Czech Republic and Southwestern Polad mainly for severe to extremely severe wind gusts, large to very large hail and excessive precipitation.

A level 2 was issued for Northern Austria, Czech Republic and Southwestern Poland mainly for severe to extremely severe wind gusts, large to very large hail and to the lesser extent for excessive precipitation.

A level 2 was issued for Northwestern to Northern Poland mainly for large to very large hail, severe wind gusts and tornadoes.

A level 1 is surrounding level 2´s with isolated events of severe weather possible.

SYNOPSIS

Refer to the storm forecast

DISCUSSION

... Northern Italy ...

Satellite loops show unseasonably strong trough crossing NW Italy at the moment with first signs of surface based development. 12 UTC soundings from Milano and Udine show backed low-level flow with 30 m/s of southwesterly flow around 500 hPa. Combined with dew points over 20°C rendering moderate degree of buoyancy, conditions look to be sufficient for an outbreak of supercells and/or bow echoes capable of damaging wind gusts and large to very large hail. In case of supercells, tornadoes will be possible too.

... Northern Austria through Czech Republic towards Southwestern Poland ...

Confidence has increased in the scenario involving a fast moving MCS moving north-northeast after 15 UTC, affecting areas from N Austria towards the central parts of the Czech Republic and Southwestern Poland. Impressive mid to upper troposphere forcing as suggested by a pronounced dry slot associated with the trough along with strong low-level convergence in the surface cyclone hint on the rapid clustering of cells that, in given conditions of strong environmental shear and moderately unstable airmass, should result in a wide swath of severe to extremely severe wind gusts. So called "tail-end Charlie" cells of the developing system might be supercells capable of large to very large hail besides severe wind gusts. Especially over the western part of the area, very heavy rainfall might also be observed, as revealed by NWP.

Level 1 was also expanded towards southeast, as surging cold front along with the trough might produce storms capable of severe wind gusts and/or marginally large hail.