Storm Forecast
Valid: Mon 10 Aug 2009 06:00 to Tue 11 Aug 2009 06:00 UTC
Issued: Sun 09 Aug 2009 19:43
Forecaster: DAHL

A level 1 was issued across N Italy for severe hail and severe convective wind gusts.

A level 1 was issued over extreme E Spain and the southwestern Mediterranean for severe hail and severe convective wind gusts.


SYNOPSIS

An elongated, positively tilted large-scale upper trough is stretching across western Europe. The southern extension of this feature is expected to close off into a fairly compact cut-off cyclone over S Iberia on Monday. The remaining low-amplitude upper trough over central Europe accelerates eastwards, with its axis reaching the German-Polish border by the end of the forecast period. At low levels, there is rather weak baroclinity, and rather flat pressure distribution prevails across most parts of Europe.

DISCUSSION

... E Spain ... SW Mediterranean ...

Sunday's 12Z ascents from Mallorca and the Spanish E coast reveal the unstable and favorably sheared nature of the air mass over the W Mediterranean and E Spain. GFS simulates a region of quite strong DLS (exceeding 40 m/s late in the afternoon) just off the Spanish E coast ahead of the intensifying upper cut-off low. MLCAPE should remain in the 1500 to 2000 J/kg range, which altogether is more than sufficient for severe evolution. Though DCVA-forced ascent will be present across the region, bulk of convection is likely to develop over land with diurnal heating. However, shear farther inland should be substantially weaker than just off the coast over the W Mediterranean. Those storms that form sufficiently far east and/or over the W Mediterranean will have fair chances of evolving into well-organized multicells and supercells. Main threats will be large hail and damaging wind gusts. However, presently it seems that coverage of storms in the favorably sheared regime will be rather low, and a LVL1 should be sufficient.

... N Italy ...

A couple of 100 J/kg will likely develop over Italy and the Balkans with diurnal heating. Over Italy, some 15 to 10 m/s DLS are simulated to be present, so multicellular storms, and maybe also isolated mesocyclones may occur. Expect isolated marginally severe hail and wind gusts with this activity.

... Mainly Germany ... Poland ... Czech Republic ...

Ahead of the central European trough, scattered storms should develop with solar heating. Though CAPE and shear will likely be quite poor, there is a slight risk of local heavy rainfall. However, probabilities seem to be too low for a LVL1 threat.

... Scandinavia ...

Scattered thunderstorms will likely develop again over Scandinavia with diurnal heating. The air mass seems to be weakly capped, and given allover weak shear, and strong LL buoyancy, some threat for non-mesocyclonic tornadoes may exist. However, uncertainty is too substantial for a LVL1 area.