Storm Forecast
Valid: Mon 14 Sep 2009 06:00 to Tue 15 Sep 2009 06:00 UTC
Issued: Sun 13 Sep 2009 20:18
Forecaster: DAHL

A level 1 was issued for the Ionian through the Aegean regions for excessive convective precipitation.

SYNOPSIS

A compact upper cut-off cyclone is slowly moving from S Germany into central France during the period. This circulation is imbedded in a large-scale quasi-stationary and positively-tilted upper trough which stretches from NW Russsia into SW Europe/NW Africa. Dominant feature on the SFC maps is an extensive two-celled high-pressure area which extends from the E Atlantic into NW Russia. Weak low pressure persists over the W Mediterranean while otherwise synoptically quiescent prevail. Focus for convective development will be the Mediterranean regions which will be affected by several weak imbedded vorticity maxima at the SE periphery of the large-scale trough.

DISCUSSION

... western and central Mediterranean regions ...

An unstable air mass lingers over the Mediterranean regions, with peak afternoon CAPEs in Sundays soundings of 1200 J/kg. This values should also be the upper end of the spectrum on Monday. Shear will vary between 10 and 20 m/s, with the maxima being rather transient and local in nature, possibly tied to mid-level vorticity maxima. This suggests that scattered thunderstorms will develop, with some severe threat existing with the strongest cells. Main threat seems to be marginally severe hail/winds, though low-level buoyancy is also forecast to be enhanced, suggesting that a few non-mesocyclonic tornadoes may occur as well. However, the allover probabilites seem to be too low to warrant a level 1 threat.

... S Ionian/Aegean regions late in the evening ...

It seems that a favorable environment for severe evolution will develop over the S Ionian and th S Aegean regions in the evening hours. Steep Saharan lapse rates should overspread the region, and shear is expected to be in the 20 to 25 m/s range. This would be sufficient for well-organized multicells and supercells. Large hail and severe wind gusts would be the main threats with this activity. However, it seems that the air mass will be strongly capped, so that initiation is rather unlikely.

... Greece early in the day ... NE Aegean/NW Turkey late in the period ...

An excessive rain threat seems to exist over Greece, moving into NW Turkey late in the period. Initially, a decaying MCS is expected to cross Greece on Monday morning. Though storm motion vectors are rather large, high amounts of precip are likely to accumulate. Later in the day, another system seems likely ahead of a vort max, which moves into NW Turkey by the end of the period. Slow motion vectors and clustering of storms could locally result in excessive precip over NW Turkey late in the light. Marginal level-one probabilities are introduced for these regions for excessive precip.