Storm Forecast
Valid: Sun 27 Sep 2009 06:00 to Mon 28 Sep 2009 06:00 UTC
Issued: Sun 27 Sep 2009 04:38
Forecaster: SCHLENCZEK
A level 1 was issued for E / SE Spain and N Morocco mainly for excessive precipitation and to a lesser extent for large hail and tornadoes.
A level 1 was issued for N Algeria mainly for large hail.
A level 1 was issued for S Italy, Sicily and parts of the Ionian Sea mainly for excessive precipitation and tornadoes.
SYNOPSIS
The zonal flow pattern over the northern parts of Europe continues through the period. Some shallow convection should be possible near the cold front of a large low pressure system centered over the Arctic Sea between Greenland and Norway. This front will cross N Scandinavia during the day. In the wake of the cold front, some cold air showers and thunderstorms are expected. Strong to severe wind gusts are possible but most of them should also occur in absence of convective cells.
Over the SW and W parts of the Mediterranean, a weak upper cut-off low will lead to unstable conditions with showers and thunderstorms. This area of relatively cold mid levels stretches further northeastward into N Italy and also towards Greece. Ahead of the core of this low, QG forcing and vertical shear will increase over Algeria and Tunisia. Increasing SFC winds over the W Mediterranean will lead to an enhanced risk of torrential rainfall and flooding in E Spain.
DISCUSSION
...E / SE Spain, Strait of Gibraltar, N Morocco...
Latest GFS runs predict MLCAPE values around 1 kJ/kg over the W / SW Mediterranean. Deep layer shear should stay between 10 and 15 m/s which favors slow moving multicells / MCSes with isolated large hail possible. Especially in the coastal areas there is a risk of excessive rainfall with peak values around 50mm in a few hours. Storms will continue through the night hours, moving to the SW. Near the Strait of Gibraltar, LL shear should be somewhat enhanced and SRH1 values around 100 mē/sē combined with high SSTs and therefore rather low LCLs indicate that tornadoes are possible. A level 1 should be warranted.
...N Algeria...
During the afternoon, QG forcing will increase from the southwest and thunderstorms are likely in this environment with about 1 kJ/kg MLCAPE. Compared to E / SE Spain, deep layer shear is stronger (up to 20 m/s) and there is a small maximum of SRH3 near 300 mē/sē forecast. Some updrafts should gain rotation and storms are likely to produce isolated large hail and strong to severe gusts.
...S Italy, Adriatic Sea, Ionian Sea...
Some hundred J/kg CAPE should be created during the day and thunderstorms are likely to develop. Although remnants of the storms of the last period will hinder insolation, some events of excessive rainfall are expected in extreme S Italy and parts of Sicily where strong LL winds lead to strong moisture advection. Besides the heavy rain threat, isolated funnels / brief tornadoes are not ruled out as the sea surface is warm and leads to LCL heights around 1 km. It is likely that storms will cluster in one or two MCSes during the afternoon, moving towards S Italy / Sicily.
