Storm Forecast
Valid: Tue 09 Jun 2009 06:00 to Wed 10 Jun 2009 06:00 UTC
Issued: Tue 09 Jun 2009 05:11
Forecaster: VAN DER VELDE
A level 2 was issued for Poland, Czech Republic. mainly for severe wind gusts and large hail.
A level 1 was issued for France, Germany mainly for tornado threat and marginally large hail.
A level 1 was issued for Baltic countries for severe wind gusts, tornado threat.
A level 1 was issued for N Italy mainly for large hail.
A level 1 was issued for E Ukraine, W Russia mainly for large hail and severe wind gusts.
SYNOPSIS
During the course of the forecast period, a low pressure area, embedded in a fairly strong southwesterly upper flow, traverses a large part of western and central Europe between Bretagne and Estonia. Shortwave troughs over northern France and over E Germany / Poland, moving through the Baltic region during the evening/night, should cause most active weather. The latter is associated with a frontal system with a narrow warm sector and unstable airmass which extends east of the warm front. The predicted cloud tops are only high in a narrow region above the surface warm front/occlusion in GFS. LCL heights are low over France and Benelux, and higher east of the cold front. They are also higher in a zone over Germany following the cold front, in which instability is possible but in a region of downward QG motion. The strongest instability is predicted in a stationary convergence zone from E Ukraine into Russia.
DISCUSSION
...France, E Belgium, Luxemburg, W Germany...
Low level shear is forecast to reach more than 10 m/s and deep layer shear over 15 m/s. Some cells could develop rotation and perhaps a tornado. LCLs are <1200 m and GFS LL CAPE is quite large. However, since there is no cap but enough large scale destabilization, storms will develop easily and plentiful, reducing the potential for isolated more potent storms.
...Czech Republic, Poland, Baltics...
00Z soundings indicate classic deeply veering and increasing winds with height between central Germany and central Poland, resulting in straight hodographs through the mid levels. CAPE will be somewhat limiting, but strong linear forcing at the occlusion has the potential of rapidly forming an MCS with the chance of gusts which may be severe in places (or more widespread). If singular storms develop, they can profit from SREH>200 mē/sē and become supercells with large hail. LLS is large-ish (10 m/s) and could support a tornado, but LCL heights are above 1500 m and cold downdrafts could reduce this potential. The situation seems better for gusts since also the 0-3 km shear vectors are perpendicular to the orientation of the occlusion, a situation favorable for bow echoes that remains during the night over the Baltics, with LLS and SREH increasing, although instability should decrease. GFS does predict a persistent large field of convective precipitation during the episode.
...E Ukraine, W Russia...
In a narrow convergence zone, SREH is >100 mē/sē, which can yield organized clustered storms with perhaps a rotating updraft. Large hail is possible, and the DCAPE>1000 J/kg and Delta-theta-e >16 support severe local gusts.
...N Italy...
Large DLS of 25 m/s and SREH > 100 mē/sē can cause isolated storms to rotate and produce large hail.
