Storm Forecast
Valid: Wed 11 Jul 2012 06:00 to Thu 12 Jul 2012 06:00 UTC
Issued: Tue 10 Jul 2012 22:04
Forecaster: PUCIK

A level 2 was issued for extreme NE Italy, N Slovenia, SE Austria and extreme W Hungary mainly for large hail, severe wind gusts and to the lesser extent excessive precipitation.

A level 1 was issued for N Italy mainly for large hail and severe wind gusts.

A level 1 was issued for Austria, Hungary, E Czech Republic, Slovakia and Poland mainly for marginally large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for NE Spain mainly for large hail and severe wind gusts.

A level 1 was issued for Central Ukraine to Russia mainly for large hail, severe wind gusts and excessive precipitation.

SYNOPSIS

At mid and upper levels of troposphere, a cyclonic vortex is forecast over the British Isles with an attendant trough moving over N Iberia during the forecast period. Between these two features, a ridge over the Central Mediterranean and the high geopotentials over the easternmost extent of the continen,t a belt of strong westerly flow will be observed, covering much of Western, Central Europe and also Iberia. Closer to the surface, a large but rather shallow low pressure system centered over Scandinavia is simulated with its frontal system stretching southwards to Central Europe. A lee cyclogenesis is likely over the southern/southeastern fringes of the Alpine range, rendering the front a wavy structure. Most of the DMC activity will be likely tied to the pre-frontal airmass.

DISCUSSION

... Spain ...

12 UTC soundings show already significant DLS over the area, which will even strengthen ahead of the quickly advancing short-wave trough, with bulk values even reaching 30 m/s. Strong forcing from the short-wave that should quickly translate over the region towards the east during the afternoon/evening hours should provide strong lift in order to weaken the CIN. However, very dry low levels will likely prevent significant destabilisation, especially inland, with some patchy CAPE simulated for the coastal areas. Still, some elevated instability from the steep EML might be released ahead of the trough with some potential for surface based storms closer to the coastline, where low level airmass becomes moister. In strong shear, any developing storm will have a potential to become a supercell, capable of large hail and/or severe wind gusts. Even though CI and its extent remain questionable, we introduce a Level 1 for this region.

... N Italy towards Slovenia, SE/E Austria and extreme W Hungary ...

Models are in relatively good agreement regarding simulating moderate degree of latent instability over the region, with some localities, especially NW Italy and SE Austria having more than 1000 J/kg of MLCAPE ready to be released. Strong DLS is forecast with values close to or over 20 m/s with increase towards the western part of the area. Lee cyclogenesis behind the Alps might back the low level flow, enhancing the shear/SREH and also providing some sfc convergence and uplift for the CI. Initiation will remain most questionable over the western Italy with storm coverage increasing towards NE thanks to the frontal zone and also the position in the left exit region of the upper level jet (Slovenia, SE Austria). Current thinking is that isolated to scattered storms will form over the region with tendency to become well organised multi or supercells with threats of large hail and severe wind gusts. Quicker storm clustering is quite likely with more widespread storm initiation over the northern part of Level 2. Only isolated CI is forecast for NW/N Italy and storms will likely not propagate very far to the south into the capped airmass over the lowlands. Still, severe and well organised convection is expected, once initiation begins and a Level 1 is issued also for this region.

... N Austria, Hungary, E Czech Republic, Slovakia, Poland ...

Ahead of the advancing cold front, DMC will likely form in the environment characterised by a marginal to moderate MLCAPE values (no significant mid-level lapse rates) and a moderate wind shear, with the values around or over 15 m/s in the 0-6 km layer especially in the western and southern part of this region. Forcing in the mid and upper levels will likely not be very significant, apart from NW Poland, which by the evening hours should be under the exit region of a mid-level jet. Initiation will be therefore tied primarily to the front, local convergence zones and topographic factors. Given the above-mentioned facts, some well organised multicells, or even a brief supercell might form, posing some localised threats of marginally large hail or severe wind gusts. Storm coverage might quickly increase in the afternoon towards the evening hours, especially in the mountainous parts (Slovakia, S. Poland) with the growth towards a one or more MCS which will move to the NE. Such MCS might pose threats of severe wind gusts and/or excessive precipitation.

... Central Ukraine to Russia ...

In the axis of the high Theta-E in the lower levels, moderate to strong instability is likely, as suggested by ECMWF and GFS output. Albeit forcing will stay rather weak, as well as the vertical wind shear (apart from the northern part of Lvl 1, where DLS around 15 m/s is forecast), pulse updrafts that develop in such environment might be capable of large hail or downbursts. Slow storm motion can promote some localised heavy rainfall and the overal threat seems to deserve a Level 1 for a rather large area.