Storm Forecast

Storm Forecast
Valid: Wed 24 Jul 2013 06:00 to Thu 25 Jul 2013 06:00 UTC
Issued: Wed 24 Jul 2013 06:40
Forecaster: PUCIK

A level 1 was issued for Ireland mainly for severe wind gusts and tornadoes.

A level 1 was issued for Morocco to Algeria mainly for severe wind gusts and large hail.

A level 1 was issued for Eastern BENELUX, Eastern France, Western Germany and Alpine area mainly for excessive precipitation and marginally large hail.

A level 1 was issued for Northeastern Poland, Lithuania and Belarus mainly for excessive precipitation.


At mid and upper troposphere, synoptic-scale pattern will feature one broad cyclonic vortex over the Eastern Atlantic and another one over Western Russia, its trough stretching towards Turkey. In between of these two vortices, an ill-defined ridge will cover parts of Central Europe and Western Scandinavia. Most of Europe will remain under rather weak steering flow, only between 10-15 m/s at 500 hPa. Closer to the surface, weakening frontal system will move from France towards Germany and further eastwards. With broad and shallow low pressure centers over the Atlantic and Russia, front itself will move in a very weak pressure field, featuring some mesoscale lows.

Generally speaking, no pronounced severe weather activity is forecast because of the lack of sufficient CAPE / strong deep layer wind shear overlap. Nevertheless, there are a few areas that deserve closer inspection and those are detailed below.


... Ireland ...

Ahead of the short-wave trough rotating around the main cyclonic vortex, warm air advection regime will establish over the region. With rather cool mid-level temperatures it seems that at least marginal CAPE build up is plausible. Weak CAPE might be compensated by quite strong forcing. Enhanced low level shear (locally over 10 m/s in the 0-1 km layer) and SREH is simulated by models in response to the WAA. However, deep layer shear will stay marginal at best, decreasing potential for supercellular convection. All in all, situation looks to be on the low-end Level 1 scale with some stronger multicells possibly capable of isolated severe wind gusts and/or weak tornado.

... Morocco to Algeria ...

Deep and dry boundary layer, along with very steep mid-level lapse rates will provide a good background for storms with high cloud bases, lots of potential for evaporational cooling of downdrafts and with most of CAPE realized in the subfreezing temperatures. Despite the vertical wind shear being moderate at best (DLS around 15 m/s), stronger multicells could be well capable of downbursts and large hail.

... Eastern BENELUX, Eastern France, Western Germany, Alpine region ...

In the weak steering flow, decaying cold frontal system is forecast to push across the region. Ahead of the front, moister airmass, characterized by mixing ratios of up to 14 g/kg will advect over the region. With only modest mid-level lapse rates, one can not expect very high CAPE values with the likely range being 500-1500 J/kg. The highest values will likely be observed over the southern extent of the area, where lapse rates will be the steepest. However, synoptic-scale "forcing" will likely be most pronounced over the northern part with the passage of a subtle short-wave, as suggested by enhanced potential vorticity fields. DMC initiation should be confined to the frontal area itself and then also with the local convergence zones or outflow boundaries left by the overnight / early morning convection.

Rather weak vertical wind shear will limit the storm organisation, with multicell cluster being the most likely convective mode. Of course, local low pressure centers with backed surface flow might slightly augment the wind shear degree. Rapid clustering of storms along the frontal boundary, weak storm motion and sufficient low-level moisture point to the fact that primary threat should be the excessive precipitation. Still, a marginally severe hail event is not ruled out with some stronger cells, especially over NW Italy and S Germany.

... Belarus, extreme NE Poland, Lithuania ...

A confluence in the low-level flow is simulated by the NWP with quite moist low-levels and mixing ratios between 10 and 12 g/kg. Synoptically speaking, WAA advection at the NW sector of the low should easily spark DMC development with the aid of an isentropic lift. Smolensk Tuesday 12 UTC sounding shows moderately moist environment with northeasterly flow. All in all, situation looks to be potent for a few excessive precipitation events with slow moving thunderstorms training along the confluence zone.

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