Storm Forecast
Valid: Tue 09 Sep 2014 06:00 to Wed 10 Sep 2014 06:00 UTC
Issued: Tue 09 Sep 2014 08:05
Forecaster: PUCIK

A level 2 was issued for NE Spain mainly for large hail and severe wind gusts.

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

A level 1 was issued for S France, Alpine region, N Italy and SE Austria mainly for excessive precipitation and large hail.

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

SYNOPSIS

A large ridge is forecast to stretch from Iberia towards Ireland as of 12 UTC, slowly drifting eastwards. To the east, a cyclonic vortex shifts slowly to the southeast, experiencing northerly prevailing flow on the forward flank of the ridge. Several, more subtle regions of lower geopotentials are revealed by the satellite lops - one, rather broad, situated over southeastern Europe and a small cut-off which will move from S France towards NE Spain.

Most of the DMC activity will be concentrated on the region just ahead of the weak cold frontal boundary, with drier and cooler airmass advecting in its wake. Scattered thunderstorms are expected in the belt spanning from E Spain towards E Poland.

DISCUSSION


... NE part of Spain ...

After several consecutive days of quite favourable severe weather conditions, situation continues in this part of Europe. 00 UTC soundings from Zaragoza and Barcelona still show steep mid-level lapse rates. With northeasterly to easterly moist onshore flow, moderate to high CAPE values are forecast near the coastline, possibly locally exceeding 2000 J/kg. As the small cut-off passes just north of the region, moderate DLS is forecast, with values ranging from 15 to 20 m/s. Scattered DMC is forecast to initiate by the afternoon, likely around the local boundaries and topography. With such degree of vertical wind shear, well organised multi and supercells will be possible, posing a risk of large hail and severe wind gusts. Small Lvl 2 is introduced for the region with the most favourable conditions for supercellular convection.

... S France, Alpine region, SE Austria ...

Comparing to NE Spain, this region will be under quite weak prevailing flow, rendering DLS values mostly below or around 10 m/s, with perhaps an expection of SE Germany. The highest CAPE values are forecast over N Italy, where the highest dewpoint values are currently observed, with some stations showing Td over 20 deg. Scattered to widespread DMC is forecast to initiate in the weak CIN values ahead of the frontal boundary and along the mountain ranges. High coverage along with slow storm motion may result in several excessive precipitation events. Furthermore, isolated large hail may be observed with stronger multicells.

... NE Poland ...

Marginal to moderate instability is forecast over this region, just ahead of the frontal boundary. Dewpoint values are on the order of 15 - 17 deg, but mid-level lapse rates are not particularly steep. Destabilisation should be aided by PVA ahead of the advancing cyclonic vortex. Degree of wind shear should increase towards the north, with extreme NE Poland having DLS values over 15 m/s. Some well organised multicells, or even brief supercells may be capable of marginally large hail or severe wind gusts in this scenario.