Forecast Update
Valid: Fri 14 Oct 2011 12:00 to Sat 15 Oct 2011 06:00 UTC
Issued: Fri 14 Oct 2011 11:54
Forecaster: TUSCHY

A level 2 was issued for Sicily, S-Italy and the coastal areas of SW-Albania and W-Greece mainly for excessive rainfall with an augmented flash flood risk.

A level 1 was issued for S-Italy, Sicily and the W-Ionian Sea mainly for severe wind gusts, large hail and an isolated tornado event.

A level 1 was issued for the S-Tyrrhenian Sea and the extreme N-coast of Algeria/Tunisia mainly for excessive rainfall.

A level 1 was issued for the central/E-Ionian Sea, parts of Greece, Albania and Macedonia mainly for excessive rainfall amounts. Waterspouts are possible along the W-facing coasts of Greece and Albania.

SYNOPSIS

Please refer to the main outlook.

DISCUSSION

... Level 2 ...

A wavy baroclinic zone is currently (12Z) placed over extreme S-Italy (e.g. Calabria), verified by HRV loop and surface data. Intense convection is ongoing mainly north of the boundary, which assists in a somewhat faster southward movement of the front compared to what models thought yesterday. Dewpoints north of the boundary stay in the lower tens in the immediate ascent region of that front and drop into the single digits further north as modified continental air mass surges southwards. To the south, upper tens and low twenties are present and reflect the high BL moisture content of that air mass.

Main reason for upgrading those areas is the messy picture of various "outflow" boundaries and convergence zones, which are well visible in HRV images next to the main W-E aligned boundary over far S-Italy. The deep layer/high-level wind field reveals a more SW-erly component with increasing S-erly winds below 850 hPa as a diffuse depression over Sicily gradually evolves. This combination is supportive for healthy thunderstorm clusters with either slow forward propagation or even backbuilding tendencies, as seen along the SW-coast of Albania and NW coast of Greece as of 12 Z. Either along those various meso-gamma or the dominant meso beta scale front, conditions are present for excessive rainfall amounts within the level 2 during the following hours. In fact, all available model data now hints on slow moving storms with excessive rainfall amounts and an increasing flash flood threat!

Please keep in mind that the shear remains supportive for large hail/strong wind gusts and an isolated tornado, mentioned and described in the first outlook. We would not be surprised to receive numerous waterspout reports, as steepening mid-level lapse rates allow the development of stronger updrafts along/atop those boundaries, e.g. along the NW/W-coast of Greece during the morning hours (in line with maximized LL CAPE and the diurnal peak of occurrence in those areas).

No major changes were performed for the rest of the outlook area. I downgraded thunderstorm probabilities over Sardinia, as a pronounced outflow of the cluster of storms over the Tyrrhenian Sea crossed the S part of the island whereas somewhat drier air now filters in from the north..