dimanche 29 juin 2014

European Storm Forecast Experiment

Storm Forecast
Storm Forecast
Valid: Sun 29 Jun 2014 06:00 to Wed 30 Jul 2014 06:00 UTC
Issued: Sun 29 Jun 2014 04:22
Forecaster: VAN DER VELDE
A level 2 was issued for N Italy mainly for severe convective wind gusts, large hail and excessive convective precipitation.

A level 1 was issued for parts of central Europe mainly for large hail.


The cold front associated with a large amplitude mid level trough from Scandinavia to the Mediterranean Sea is pushing eastward through Italy and central Europe today. Surface level lows reside over southern Scandinavia and northern Italy. Cold airmass thunderstorms are likely over France, Benelux and western Germany. The prefrontal airmass over Italy is moderately unstable due to the presence of the Saharan Air Layer with steep mid level lapse rates and 10-12 g/kg moist boundary layer air. Strong winds in mid levels create a favorable kinematic environment for storms.


...Italy, southern Austria and western Balkan...

Some regional WRF models predict over 2500 J/kg SBCAPE over the Lgurian Sea. MLCAPE should be 1000-2000 J/kg. This will be capped south of the Po valley. Either way, given the 20 m/s deep layer shear and strong moisture lifting over the south slopes of the Alps triggering of supercells and MCSes is highly probable, with chances of widespread large to very large hail and severe wind gusts. During the evening as the cold front comes through, the model scenario (GFS, WRF) is that some discrete supercells or a linear system will also affect the area south of the Po valley. The area of Austria to Croatia will likely see the strongest moisture lift and largest storms, and can become affected by excessive convective rainfall, at least locally. The PV/dynamic tropopause intrusion acquires a negative tilt at night which might help to keep the storms active for long in the region near Slovenia, although WRF models keep the storms moving. Tornadoes are not ruled out with pre-Alpine 0-1 km shear of 8 m/s and locally higher.

...Hungary, N and E Austria, Czechia, Slovakia, Poland, Lithuania...

Relatively modest MLCAPE should exist in a broad area from Hungary/Austria to the Baltics. The presence of 10-15 m/s deep layer shear could develop persistent and rotating updrafts which can locally release large hail. The frontal convergence zone in the Austrian-Hungarian-Czechian borders region should be the main focus for convective development, another is NE Poland and Lithuania near the occlusion.

...southern Sweden and Norway...

Some instability is present within the low. Low cloud bases and slow cell motion combined with good low-level buoyancy and convergence zones are found mainly over southern Sweden. Such conditions are favorable for spout type tornadoes and funnels.

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