Storm Forecast
Valid: Mon 09 Nov 2009 06:00 to Tue 10 Nov 2009 06:00 UTC
Issued: Mon 09 Nov 2009 05:39
Forecaster: SCHLENCZEK
A level 1 was issued for the central Mediterranean / Tyrrhenian Sea mainly for waterspouts.
A level 1 was issued for the Ionian Sea and southern / western Greece mainly for severe wind gusts and excessive precipitation and to a lesser extent for tornadoes and large hail.
A level 1 was issued for NW Greece and parts of the SW Balkans mainly for excessive precipitation.
A level 1 was issued for NE Italy, N Adriatic and Slovenia mainly for tornadoes and severe wind gusts and to a lesser extent for excessive precipitation.
SYNOPSIS
The most important feature for deep moist convection on Monday is an upper cut-off low centered over the Gulf of Genoa. A 1000 hPa surface low near the upper cold core is forecast to move southeastward towards the Ionian Sea. Strong southerly / SSWerly winds ahead of the low advect warm and moist air to Greece and the Balkans where heavy convective rainfall is expected in the next 48 hours.
An occluding low pressure system over the East Atlantic will affect the British Isles in the afternoon / evening hours. The cold front which should cross Ireland during Monday afternoon is forecast to weaken, but some low-end instability near the occlusion point may lead to showers and thunderstorms over SW Ireland, Wales, SW / S England and extreme NW France. Other regions remain rather quiet as cold air overspreads large portions of eastern and central Europe and an upper ridge stretches northeastward from Iberia towards France.
DISCUSSION
... C Mediterranean, Tyrrhenian Sea...
Some hundred J/kg CAPE should be available in most parts of the western and central Mediterranean. Deep layer shear will be in order of 10 m/s, so most of the showers / thunderstorms will be briefly organised multicells. Weak shear at lower levels and steep lapse rates in an almost uncapped airmass may allow some waterspouts. Other types of severe weather are unlikely.
...SE Italy, Ionian Sea, Greece, S Balkans...
In the vicinity of the jet streak / left exit region over the Ionian Sea and S Adriatic, some hundred J/kg MLCAPE are forecast. QG forcing will strengthen during the afternoon as an upper vort-max approaches Greece. The environment is strongly sheared with deep layer shear in order of 25 - 30 m/s. Ahead of the trough, easterly / southeasterly low level winds are observed and LLS as well as SRH3 are locally enhanced (100 - 150 mē/sē). The main convective mode is expected to be organised multicells and some supercells in the southeastern half of this level 1 region which will pose a threat of isolated large hail, severe gusts and a possible tornado. As the storms move northeastward into N Greece / Balkans, upper level flow becomes more parallel to the frontal boundary. Storms will persist for some hours over this region, especially in the late evening / night hours which leads to an enhanced heavy rainfall threat.
...N Adriatic, NE Italy, Slovenia...
A small region in the N Adriatic will get MLCAPE around 500 J/kg in an environment with 20 - 25 m/s deep layer shear. Upper level winds from SSE and LL winds from E / NE create strong directional shear and a spot of enhanced SRH3 at the northern tip of the Adriatic Sea. Thunderstorms which develop in this region are likely to become supercellular and may produce severe gusts and large hail. Tornadoes are also possible, given steep LL lapse rates, 10 m/s of LLS and a high probability of mesocyclonic storms.
...SW Ireland, Irish Sea, Wales, SW England, extreme NW France...
Ahead of the cold front of an occluding surface low, a few hundred J/kg are forecast in a region with strong deep layer shear and enhanced SRH3. Storms will probably organise into multicellular lines which may produce an isolated severe gust and / or a brief tornado but overall storm coverage is probably too low for a level 1.
Strong deep layer shear and a few hundred J/kg CAPE are also forecast for the S Bay of Biscay but rather weak QG forcing as well as low level CAA in the wake of the trough should limit the potential of severe thunderstorms. An isolated severe gust is not ruled out, though.
