Storm Forecast
Valid: Sun 25 Oct 2009 06:00 to Mon 26 Oct 2009 06:00 UTC
Issued: Sun 25 Oct 2009 05:57
Forecaster: SCHLENCZEK
A level 2 was issued for Crete and S Greece mainly for widespread excessive precipitation and large hail and to a lesser extent for tornadoes and severe wind gusts.
A level 1 surrounding the level 2 was issued for Greece, Aegean Sea and parts of W Turkey mainly for excessive precipitation.
SYNOPSIS
A stationary upper trough is centered over the central Mediterranean and a surface depression has developed in the left exit region of a 35 m/s upper jet streak ahead of this trough, affecting parts of Greece and Turkey on Sunday. A small tongue of warm and moist air stretches from the E Mediterranean into S Turkey and the Aegean Sea. In the wake of the trough, dry and moderately warm air is advected southward into N Italy and W-central Mediterranean towards Tunisia.
An occluding surface low over Scotland is forecast to move eastward. Its frontal system is now located over E Germany and weakens during the period. In the wake of the low, an upper trough approaches the North Sea, leading to some low-end instability which will allow showers and thunderstorms.
Dry and mostly stable conditions are expected in a broad area from the N Maghreb States and Iberia towards Poland and NW Russia where high pressure will prevail. Only some parts of central Iberia may get a chance of diurnally driven thunderstorms.
DISCUSSION
...Iberia, SW Mediterranean...
A few hundred J/kg of CAPE are forecast to be created during the day in a warm and moist airmass. Diurnal heating may lead to isolated to scattered showers / low-topped thunderstorms over the mountainous regions that will probably not become severe as no significant deep layer shear is in place and storms will probably not become deep enough to produce heavy rainfall that matches the level 1 criterion.
...SE England, North Sea, Netherlands, NW Germany, Denmark...
A broad area with 100 - 300 J/kg CAPE is expected over the North Sea in the vicinity of the trough axis which will cross SE England around midday. QG forcing should be strong enough for convective initiation and in this moderately sheared environment, storms will likely become multicellular and may organise into narrow lines. Small hail and strong to marginally severe gusts are possible with the strongest storms. A threat level has not been issued.
...Aegean Sea, S Greece, Crete...
Continous advection of very moist air from the E Mediterranean in a strong and deep southeasterly flow will lead to MLCAPEs in order of 1 - 1.5 J/kg over the E Mediterranean and most parts of Greece and W Turkey. Even though QG forcing is forecast to decrease during the period, orographic lift should be strong enough to maintain thunderstorm activity. The main convective mode should be one or two large MCSes with a threat of widespread excessive rainfall and locally large hail / severe gusts. Apart from the heavy rainfall threat, an isolated tornado may occur in a region with locally enhanced LL shear as LCL heights are very low.
Recently, a back-building MCS is present over Crete, moving slowly to the northwest. A threat level 2 has been issued for widespread excessive rainfall with a high probability of flash floods.
