Storm Forecast
Valid: Wed 29 May 2013 06:00 to Thu 30 May 2013 06:00 UTC
Issued: Wed 29 May 2013 07:56
Forecaster: PUCIK
A level 1 was issued for the Balearic Sea mainly for large hail and severe wind gusts.
A level 1 was issued for Northwestern Italy mainly for large hail.
A level 1 was issued for Eastern Bohemia, Moravia and Southern Poland mainly for large hail and to the lesser degree for severe wind gusts.
A level 1 was issued for Serbia to Southeastern Hungary and Western Romania for large hail and severe wind gusts.
A level 1 was issued for Estonia and Russia for large hail and to the lesser degree for severe wind gusts.
SYNOPSIS
Situation is still dominated by a large cyclonic vortex centered over France with its main trough stretching from Northern Germany through Poland towards Belarus. Southern and western flanks of the vortex are engulfed in strong mid and upper tropospheric flow with an Azorian high ridge slightly amplifying towards northeast. Core of the jet-stream should lie over the Mediterraneans, copying the northern extent of the main frontal zone. Closer to the surface, center of the low will lie over Northeastern Germany, its trough stretching to the Czech Republic. Most of Western Europe is under rather significant cold air advection.
Quite widespread tstm activity is forecast today - mainly thanks to the presence of large scale vortex filled with unseasonably cold mid-level temperatures, moist environment and low LFCs. However, only few areas will have any chance for severe weather - limiting factors should be quite poor low level moisture and insignificant overlap of CAPE / vertical wind shear.
DISCUSSION
... Balearic Sea ...
Strong mid-level jet is forecast to cover this area, yielding DLS values above 25 m/s. As cold mid-level air spreads over moist boundary layer of the sea, NWP point to the build up of moderate CAPE values. Such overlap would certainly be conducive for isolated well organised and severe DMC, including supercells capable of large hail and severe wind gusts, but the main uncertainity remains in the field of initiation. The most probable period of DMC development will the late evening to night hours, as mid-level trough approaches the region (although e.g. ECMWF still produces only very spotty and small amounts of precip). Will keep a Level 1 for very isolated severe weather in this area.
... France ...
Very cold mid-tropospheric airmass spreads over the area, contributing to steep lapse rates and rather low height of 0°C isotherm. Thus, even with pulse-type DMC in very weak vertical shear, potential will exist for some very isolated marginally severe hail event with stronger updrafts.
... Eastern Bohemia, Moravia, Southern Poland ...
Ahead of the surface trough, moister southeasterly flow has established over region with dewpoints barely exceeding 10°C. With not particularly steep mid-level lapse rates (albeit a patch of 7 K/km is notable from Vienna 00 UTC sounding and will advect towards north during the day), CAPE values are not expected to be very high, possibly only around 500 J/kg using the mixed-layer method. Around 15 m/s of southwesterly flow at mid troposphere should yield moderate vertical wind shear degree with some veering in the lower levels. Thus, some well organised DMC is not ruled out in this setup. Storms will likely initiate along the convergence zone of the advancing trough or around the major orographic features (LFC levels will be quite low so initiation should not pose too much trouble). Primary threats should be marginally large hail and/or marginally severe wind gusts in case that storms form a "quasi-linear" system along the convergence zone. A low-end Level 1 is introduced for this region.
... Northwestern Italy ...
Moderate deep layer shear might enhance degree of DMC organisation as the storms track along the rim of the Alpine range. Steep mid-level lapse rates and very cold mid level temperatures enhance the risk of isolated large hail.
... Northern Serbia to Southeastern Hungary and Western Romania ...
Moderate degree of latent instability is forecast for the region thanks to the steep mid-level lapse rates, as supported by 00 UTC Beograd sounding. 10-15 m/s of DLS might allow for at least limited storm organisation into multicells, which might be capable of large hail and/or severe wind gusts due to the rather dry boundary layer. DMC initiation will be most likely towards the evening and night hours as the PVA spreads over the region with the approach of the short-wave trough and convergence zones establish over the region. Storms will likely spread further towards northeast, possibly forming MCS.
... Estonia to Russia ...
An isolated severe weather event is not ruled out in the environment of 15-20 m/s 500 hPa flow and low level moisture convergence along the advancing frontal zone. Primary threat should be marginally large hail, severe wind gusts will be mostly limited by lack of low-level shear.
