Storm Forecast
Valid: Sun 20 Sep 2009 06:00 to Mon 21 Sep 2009 06:00 UTC
Issued: Sat 19 Sep 2009 23:27
Forecaster: SCHLENCZEK
A level 1 was issued for SE Italy, SW Greece and parts of the Ionian / Aegean Sea mainly for excessive rainfall and large hail.
SYNOPSIS
On Sunday, deep moist convection is expected mainly in the vicinity of an upper cut-off low which is centered over S France. Ahead of this low, very moist and warm air is advected to the Ionian Sea and the western and southern parts of Greece. Near the center of the upper low, unstable conditions are also expected in the western and central Mediterranean. Another tongue of warm and moist air stretches from Italy towards N Germany. Stable conditions are expected in most parts of NE Europe, W Iberia and the British Isles.
DISCUSSION
...E Spain, Balearic Islands, SW Mediterranean...
In the late morning hours, an upper vort-max will overspread E Iberia from the west. Some low-end instability should be in place and strong vertical wind shear will lead to some organized multicells which may produce isolated large hail. Storms will move eastward during the afternoon, affecting parts of NE Morocco and N Algeria and the Balearic Islands. As instability is limited to a few hundred J/kg, the large hail threat should not be sufficient to exceed the LVL1 threshold.
...E France, S Benelux, S / central Germany...
No well-defined upper level feature as a source of large-scale ascent is forecast for this region with some hundred J/kg of CAPE. In this environment with less than 10 m/s deep layer shear, diurnally driven showers and thunderstorms will form. Some of them may pose a threat of marginally severe hail but storm coverage and severity is too marginal for a LVL1. Only a small number of storms may persist after sunset when most of the CAPE will diminish.
...Italy, Adriatic Sea, Balkans...
Over large portions of Italy / Adriatic Sea and the N Balkans, MLCAPEs around 500 - 1000 J/kg are forecast in an environment with 10 - 15 m/s deep layer shear. Most of the storms should be multicellular and may produce moderate rainfall and marginally severe hail. If storms manage to merge into a large MCS, heavy rainfall could lead to flooding.
...Ionian Sea, SW Greece, SE Italy...
Ahead of a small upper vort-max, MLCAPE may reach values around 1000 J/kg over the S Aegean Sea and SW Greece. This feature should provide enough lift for initiation and organized multicells as well as a large MCS may form in this area with 15 - 20 m/s deep layer shear. GFS simulates very high rainfall rates for SW Greece but it is questionable whether storms will reach the coastal area or stay overseas. The main threat should be excessive rainfall but isolated large hail may be possible as well.
...S Turkey, extreme E Mediterranean...
As the upper trough over the Black Sea region moves southeastward, very warm and moist air is advected towards S Turkey. Latest runs of GFS show about 1.5 kJ/kg MLCAPE that will be released in the afternoon hours. Vertical shear is quite weak in the whole area and a few briefly organized multicells may produce a funnel / brief tornado and / or isolated large hail. Most parts of the affected area are outside of the ESTOFEX forecast map.
