Storm Forecast
Valid: Sun 06 Sep 2009 06:00 to Mon 07 Sep 2009 06:00 UTC
Issued: Sun 06 Sep 2009 01:06
Forecaster: SCHLENCZEK

A level 1 was issued for parts of the Balkans mainly for excessive rainfall and to a lesser extent for large hail and severe gusts.

SYNOPSIS

An upper trough over the W Baltic Sea will move northeastward during the period while weakening. Isolated showers and thunderstorms are expected in the vicinity of this trough in an environment with a few hundred J/kg CAPE.

Another upper trough over the Adriatic Sea shifts eastward, affecting the Balkans and extreme S Italy. Most of the convection should be associated with a frontal boundary that stretches from the W Black Sea via Greece and Albania towards S Italy and N Algeria / Tunisia.

A frontal wave west of Ireland will move across Ireland and most parts of the UK during Sunday afternoon. Near the cold front there is only little instability forecast and organized deep moist convection is unlikely.

DISCUSSION

...S Italy, Balkans, W Black Sea region...

On Sunday afternoon, GFS shows about 500 - 1000 J/kg CAPE in the trough region with less than 10 m/s deep layer shear in most parts of the area and only weak signals of QG forcing. Some slow moving storms may pose a threat of excessive rainfall and isolated severe gusts / large hail, especially over SW Bulgaria. In the late night hours, storms should gradually weaken and severe weather should become more unlikely.

...N Algeria, N Tunisia...

Some hundred J/kg CAPE are forecast in a region with very weak vertical shear and forcing. In the afternoon / evening, isolated to scattered thunderstorms are forecast with isolated severe gusts possible due to evaporative cooling. At this moment, overall threat seems to be too low to issue a level 1.

Thermodynamic and kinematic conditions are almost the same in eastern / southeastern Spain. An isolated large hail / strong gust report is not ruled out but severe weather should be rather unlikely.

...Baltic region...

In the wake of the trough, a few hundred J/kg of CAPE will be created by cooling at mid levels. Rich BL moisture will lead to LCL heights around 500m. Combined with steep LL lapse rates and weak wind fields, this may allow an isolated funnel / waterspout over the Baltic Sea. Compared to the days before, lapse rates and CAPE have decreased which will minimize the waterspout threat. At this moment a level 1 is not warranted.