Storm Forecast
Valid: Mon 01 Jun 2009 06:00 to Tue 02 Jun 2009 06:00 UTC
Issued: Sun 31 May 2009 22:27
Forecaster: SCHLENCZEK
A level 1 was issued for S Belarus and N-central Ukraine mainly for large hail.
A level 1 was issued for S-central Italy and the S Dinaric Moutains mainly for excessive rain and large hail.
SYNOPSIS
On Monday, severe weather should only be possible in the vicinity of an upper cut-off low over SE Poland / Slovak. Rep. Initially, the trough axis is W-E oriented but this will change through the period as a longwave trough over N Scandinavia will dig southward. An upper jet streak circles around the low pressure system with a maximum of 25 m/s at 500 hPa near Sicily. In this moderately warm airmass around the upper low, MLCAPE will stay below 1000 J/kg in most places. At the eastern flank of the low, very warm air is advected northward into southern Russia.
DISCUSSION
...N France, Belgium, SW-central Germany...
Ahead of the low pressure system, diurnal heating may lead to about 500 - 1500 J/kg CAPE which should result in briefly organized multicells and pulsating storms as DLS will stay below 10 m/s. A few storms should nevertheless be capable of producing isolated large hail and severe wind gusts but overall threat will remain rather low. Rich BL moisture and a slow expected storm motion may lead to heavy rainfall which will locally result in flash floods. According to the latest runs of GFS and WRF, storms should develop over central Germany and the eastern parts of France / Belgium in the late morning / early afternoon and dissipate over C France in the late evening / night hours. The coverage of severe thunderstorms should be too low for a level 1.
...Belarus, SE Baltic States, N Ukraine...
Southerly LL winds advect a warm and moist airmass from N Ukraine into S Belarus. In the early afternoon, about 1,5 kJ/kg weakly capped MLCAPE should be present in that region. Deep layer shear will reach values up to 15 m/s which should be sufficient for organized multicells and maybe also a few supercells. The first storms that initiate may produce large hail and severe gusts. As the cap will completely disappear, storm coverage will increase and storms will tend to merge into a MCS with excessive rainfall in some places. The hail / gust threat will diminish substantially after sunset.
...C Mediterranean, S-central Italy, Balkans...
Some hundred J/kg CAPE should be present in a region from SE France and central Italy down to N Tunisia and Sicily. In the afternoon, some upper vort-maxima will overspread the region, leading to thunderstorm development. In the southern part of the area, deep layer shear may reach values up to 20 m/s which allows some organized multicells that may produce isolated large hail but the main threat should be excessive rainfall as there is rich BL moisture and numerous storms will move across the same region. According to GFS, the 24h accumulated precipitation may locally exceed 120mm. Later in the evening, the storms will move eastward, affecting the western part of the Balkan peninsula. The excessive precipitation threat will persist.
