Storm Forecast
Valid: Fri 07 Nov 2014 06:00 to Sat 08 Nov 2014 06:00 UTC
Issued: Thu 06 Nov 2014 15:41
Forecaster: TUSCHY

A level 2 was issued for parts of S-Italy, Greece and Albania mainly for excessive rain.

A level 1 was issued for parts of the CNTRL/E Mediterranean mainly for excessive rain, isolated large hail, tornado and severe wind gusts.

SYNOPSIS

A longwave trough digs south and interacts with hot continental air over N-Algeria. The result will be a spin-up of a rapidly deepening vortex in the low/mid troposphere. A chunk of energy tries to choke off the westerlies over Sicily, but a complete cut-off is not yet anticipated. Nevertheless a healthy upper low moves over Sicily and dictates the severe risk for the region.
Progressive pattern with numerous troughs (with fluctuating amplitudes) affects NW Europe, where cooling mid-levels heralds a period with active marine convection.
Elsewhere, ridging and/or marginal BL moisture preclude (organized) deep convection.

DISCUSSION

... S-CNTRL Italy, Greece and the Tyrrhenian, Ionian, Adriatic and Aegean Sea ...

Widespread shower/thunderstorm activity continues from the previous night as impressive warm conveyor belt (WCB) remains in place over the Ionian and Adriatic Sea. The WCB shifts east during the forecast with a constant weakening trend seen in most models. During the day, widespread rain due to persistent isentropic lift is forecast over the eastern coasts of the Adriatic and Ionian Sea. Strength of low/mid-level winds, lift/forcing and upper divergence point to an excessive rainfall risk with embedded (elevated) convection possible. This risk also affects Greece during the evening and overnight hours before some weakening is expected over the Aegean Sea during the end of the forecast, as the winds start to relax. The highest risk for flash flood producing rain remains along the coasts, where back-building convection is likely. A similar risk also exists for most of Greece, where strong low/mid-level flow and modest onshore CAPE overlap. Orographically forced training convection with local excessive rain is possible. LL shear (especially directional shear) increases along the coasts, where a few tornado reports are likely. In addition, a 30 m/s 500 hPa jet streak starts to phase with eastbound moving CAPE tongue, so Greece may see also organized DMC activity with an isolated tornado , large hail and severe wind gust risk. Latest forecast soundings for Greece show a rather large onshore fetch of surface based convection, before activity turns more elevated over N-Greece. It has to be noted that model discrepancies regarding the upper low's position remain
noteworthy, which could delay thunderstorm activity over Greece until the very end of our forecast period.

Sicily will be placed beneath the center of the upper low. Cold mid-levels atop the warm SSTs allow 500-100 J/kg MLCAPE build-up with widespread thunderstorm activity. Final track of the vortex determines the final severe risk for Sicily. Latest guidance brings the center over extreme S-Sicily before
departing east. This would yield enhanced convergence and onshore flow for NE Sicily. Any storm would be a slow mover due to weak steering flow and excessive rain becomes the main risk. An isolated tornado event can't be excluded due to 150-200 J/kg LLCAPE. During the night the main thunderstorm activity shifts east towards the Ionian Sea.


... S-UK ...

Onshore moving marine convection may help to mix stronger winds down to the surface (850 hPa with 20 m/s). A few strong to severe wind gust events are likely. The main / best structured activity however remains offshore over the English Channel. Flat ridging suppresses convection during the night from W to E.