Storm Forecast
Valid: Wed 10 Dec 2008 06:00 to Thu 11 Dec 2008 06:00 UTC
Issued: Tue 09 Dec 2008 21:30
Forecaster: PUCIK

SYNOPSIS

A blocking pattern will persist over Europe as a deep trough at midlevels is increasing in amplitude. Its axis will stretch from Scandinavia to Algeria with strong mid-level flow surrounding it. On the other hand, eastern part of Europe will be dominated by a ridge. In the lower levels, large high pressure system is anticipated across eastern and northeastern parts of Europe. Low pressure systems, observed under the mid-level trough, are expected to slowly fill, whereas western part of Mediterranean should experience cyclogenesis. Cool and stable airmass will dominate most of the continent, guaranteeing too hostile conditions for thunderstorm development, except for the above mentioned region of W Mediterranean.

DISCUSSION

...W Mediterranean...

A tongue of steep mid-level lapse rates is being advected over the warm SSTs on the forward side of the surface low. This pressure system is expected to deepen slightly and move eastwards, under the influence of the mid-level impulse. Center of the low should be placed over Nicosia and Corsica by the end of forecast period. In response, belt of instability is expected to form ahead of the low, in the region of WAA, stretching from Tunisia to the Tyrrhenian Sea. The highest degree of destabilization is expected in the evening/night hours when MLCAPE values might reach 1000 J/kg. This will be also the time, when the highest thunderstorm coverage should be observed. DLS values should stay around 15 m/s, therefore, multicellular storm mode will prevail. A slight veering of the winds with height is also expected, as the surface low will deepen, and an isolated enhancement in SREH values is possible, especially over the coastal areas of Italy. Nevertheless, chance of supercells will stay low and only marginally severe hail can occur with the strongest cells.

The highest threat should be the waterspout activity. Robust LL instability release is predicted by GFS, especially over the western coasts of Italy. Moist airmass over the sea should contribute to the low LCLs and strong convergence signals are generated by models. Level 1 is issued for the region, where the best overlap of the above mentioned factors will exist but few waterspout reports might occur also out of this threat area.