STORM FORECAST
VALID Sat 11 Mar 06:00 - Sun 12 Mar 06:00 2006 (UTC)
ISSUED: 11 Mar 00:28 (UTC)
FORECASTER: DAHL

SYNOPSIS

Large-scale quasi-stationary upper trough is located over central Europe. Intense peripheral short-wave trough is rapidly progressing southward into the Mediterranean ... thereby amplifying and evolving into a cut-off low over the central Mediterranean towards Saturday evening. Upstream vort max will likewise move into the NW Mediterarnean late in the period. Main SFC cold front associated with a previous trough ... should extend from the S Ionian Sea NEWD across Greece into the N Balkans ... and merge with upstream cold front associated with the intense s/w trough late in the period as a result of rather vigorous cyclogenesis over the NW Mediterranean. There will be three potential foci for convective development on Saturday. One along and ahead of the main Mediterranean cold front ... one along and ahead of the second/weaker cold front upstream ... and in the post-frontal environment beneath the developing thermal-low center.

DISCUSSION

...Ionian and Aegean Sea ... S Balkans...
12Z ascents did not capture the instability of the prefrontal air mass which is revealed by rather widespread lightning activity over the Ionian-Sea region ... and backed by Satellite imagery and model CAPE fields. Indications are that weak instability will persist through Saturday along and ahead of the main cold front over the Aegean and S Balkans. Mid-level flow of 20 to 25 m/s ... and 850 hPa winds of about 15 m/s should allow for some organization of the TSTMS ... though strongest dynamics and shear profiles should remain farther upstream near the cyclogenesis. However ... late in the period ... warm/unstable air will eventually be integrated into the low's circulation which may result in an early-morning rejuvenation of the convective activity over the S Aegean/Ionian Seas. ATTM threat appears to be too marginal for a level one risk though an isolated severe TSTM event ... including marginally severe hail/winds and possibly a tornado or two ... could occur. An upgrade may be considered with later outlooks.

...central and weatern Mediterranean...
Upstream ... instability in the small warm sector associated with the developing cyclone over the NW Mediterranean is uncertain. Strong dynamic forcing for UVVs and evaporation from the Sea may act to create weak CAPE ... and it seems that at least shallow TSTMS could be possible. Shear should be strong enough to support an isolated severe TSTM event ... but little confidence in widespread TSTM development along/ahead of the cold front preclude a categorical risk ATTM though an upgrade may be necessary if TSTM coverage is greater than currently anticipated.

Shallow convection will likely develop in the postfrontal environment beneath developing upper thermal low. This activity may be rather shallow and fail to become well-organized given the lack of strong low-level forcing for UVVs ... but an isolated shallow mesocyclone with an attendant tornado threat could occur given rather strong shear. Threat should be too low however for a level one.

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