Storm Forecast
Valid: Fri 25 Jan 2013 06:00 to Sat 26 Jan 2013 06:00 UTC
Issued: Thu 24 Jan 2013 22:05
Forecaster: TUSCHY

A level 1 was issued for W-Greece and the NE Aegean Sea mainly for an augmented waterspout risk (offshore), heavy rain and isolated large hail.

A level 1 was issued for extreme SE Italy mainly for heavy rain.

SYNOPSIS

Normalized GPH anomalies in addition to analogous height analyses confirm ongoing weak and disturbed polar vortex with at least two major vortices: the first one, which was anchored atop the Hudson Bay for the past few days gradually shifts east/northeast. Attendant impressive height gradients (e.g. 90-100 "500 hPa gpdm" difference from Greenland to the subtropical Atlantic) assist in rapidly increasing baroclinity and numerous intense vortices (at least one of those will be a tremendous warm-seclusion process with an explosive deepening rate of at least 60 hPa during my forecast period far south of Greenland). This increase in activity will have an influence on the far western part of Europe, where deep tropospheric warming spreads east.

The second vortex (less well defined) is still placed over far N/NE Europe, where the coldest air of Europe at all levels will be found. However at 500 hPa, low heights extend far south and cover most of Europe with surface high pressure in place over C-Europe.

DISCUSSION

... C/E Mediterranean ...

A 995 hPa depression shifts from Sicily to Greece with no real change of strength expected. Activity will be scattered to widespread due to the enhanced T850hPa-SST difference and the proximity of a 40 m/s mid-level jet and its exit region. This configuration assists in well separated shear/instability fields. However, modest LL CAPE, weak background shear and expected convergence along the coasts (e.g. W-Greece and W-Turkey) may cause a few waterspout reports. Stronger cells will be able to produce marginal hail (an isolated large hail event not ruled out) and tendency of rapid upscale growth of cells may also result in heavy rain (especially along the E-coast of the Ionian Sea and the NE/E coast of the Aegean Sea).

... Bay of Biscay 18 Z onwards ...

A combination of a southward sliding cold front beneath a rapidly amplifying mid-level trough result in a concentrated swath of low-end to moderate MLCAPE build-up. Favorable dynamics beneath the left exit of a 50 m/s mid-level jet may spark scattered thunderstorms, which spread southeast and affect extreme W-France during the second part of the night. Expected dynamics and the proximity to strong shear show a slight possibility for an organized storm or two with isolated large hail/severe wind gusts the main risk. This risk will be too low for a level 1 right now. However, if showers/thunderstorms remain anchored to the strong UVV field, a better organized line of DMC may cause a stronger wind event and an upgrade could become necessary later-on.