dimanche 18 mai 2014

European Storm Forecast Experiment

Storm Forecast
Storm Forecast
Valid: Sun 18 May 2014 06:00 to Mon 19 May 2014 06:00 UTC
Issued: Sun 18 May 2014 05:38
Forecaster: TUSCHY
A level 2 was issued for parts of the Ukraine, Belarus Latvia, Lithuania and S-Estonia mainly for severe to damaging wind gusts, a few tornadoes (a strong event possible) and large to very large hail.

A level 1 surrounds the level 2 area mainly for a similar risk but with less confidence in extreme events.

A level 1 was issued for NE Morocco and NW Algeria mainly for a few large hail events and excessive rain.


The lengthy and spacious upper low over SE Europe, which wreaked havoc in numerous countries now lifts towards Denmark and opens up into an upper trough, which runs from the North Sea all the way to the Black Sea. Downstream ridge over W-Russia strengthens and evolves into a blocking anticyclone. In the meantime, another major trough west of Ireland builds south and approaches the far NW Iberian Peninsula during the end of the forecast. This trough becomes the next feature which ensures a continuance of the blocking pattern over most of Europe.

The most interesting boundary, convective-wise, will be a wavy quasi-stationary baroclinic zone, which runs from the CNTRL Baltic Sea to the Ukraine. Atlantic fronts approach the Bay of Biscay and Portugal/Spain but most likely will not yet have any influence on our thunderstorm forecast.


...NW Poland and NE Germany until 12 Z...

The dissolving and slowly NW-ward drifting vortex still continues to wrap an occlusion around its center, which ensures an ongoing advection of moist and unstable air to NE Germany. The front becomes quasi-stationary over NE Germany and dissolves. During the start of the forecast, a cluster of showers/thunderstorms moves along that tongue of unstable air towards NE Germany. This cluster is accompanied by heavy rain and gusty winds. A temporal upswing of lightning activity is forecast during the forenoon hours, before probabilities decrease around noon as CAPE wanes due to an extensive area with stratiform rain. Embedded convection can still cause heavy rainfall amounts with slow moving convective elements and effective PWs in excess of 20 mm.
Over NW Poland, the occlusion gradually lifts north and probably moves offshore around noon. Until then, scattered thunderstorms continue and grow upscale into smaller clusters with heavy rain and marginal/isolated large hail. However, as some models and synop data continue to show a closed cyclonic circulation center at the surface, LL shear may remain somewhat enhanced over extreme NW Poland to support an isolated tornado event before noon (SRH-1 around 100 m^2/s^2 and LCLs below 600 m). This risk ends around noon. The overall risk seems to be too marginal for a level 1.

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