Storm Forecast
Valid: Mon 08 Aug 2011 10:00 to Tue 09 Aug 2011 06:00 UTC
Issued: Mon 08 Aug 2011 10:47
Forecaster: KOROSEC
A level 2 was issued for the southern Alpine region including extreme S Austria, most of Slovenia, NE Italy, N Adriatic sea and parts of Croatia mainly for excessive convective rainfall, strong/severe wind gusts and lesser extent for tornadoes and large hail.
A level 1 was issued for surrounding areas of level 2 across the northern Mediterranean mainly for intense rain and strong wind gusts and lesser extent for brief funnel/tornado.
A level 1 was issued for southern and eastern Germany, western Poland, Czech Republic and northern Austria mainly for severe wind gusts, large hail and weak funnels/tornadoes.
A level 1 was issued for the areas from northern Balkans into NE Europe and NW Russia mainly for large hail, tornadoes, excessive convective rainfall and strong wind gusts.
A level 1 was issued for parts of N Marocco and Algeria mainly for large hail and strong/severe wind gusts.
SYNOPSIS
A complex setup across Europe today with the robust upper long-wave trough crossing N-CNTRL Europe. An unsesonably strong 50-60 m/s mid level jet rounds the base of the trough providing ample shear for organized severe storms. At surface, a large cyclone sits centered over Scandinavia with double cold front feature. One front extends from Finland SSW-wards towards the N Balkans while the main (strong) cold front crosses central Europe.
DISCUSSION
... extreme S Austria, most of Slovenia, NE Italy, N Adriatic sea and parts of Croatia ...
An active convective weather is expected for parts of the southern Alpine region today as the strong cold front crosses the Alps later in the forecast period. Warm and very humid BL moisture continue to advect across the region today, with near-surface mixing ratios between 12-14 g/kg and SFC dewpoints around 18-24°C. Morning soundings reveal very strong shear already in place, as well as high moisture content throughout the troposphere. Combined with several hundreds J/kg of MLCAPE available, this will lead into continued orographic rainfalls due to persisting SW flow and advecting moisture from the Mediterranean. Locally, a large amount of rain has already fallen and this threat should continue until the evening hours.
Later in the afternoon/evening when well-defined DCVA and a strong cold front arrive across the Alps, strong QG forcing should initiate numerous storms along/just ahead of the front. Its possible that some storms could also form earlier along the pre-existing SFC convergence zones, but the activity seem more likely to occur with the arrival of the front. Steepening lapse rates above the high BL moisture should release moderate instability in strongly sheared environment. Deep layer shear in excess of 30m/s and SREH3 of around 200-300 m^2/s^2 favours supercell and multicell storms, capable of producing mainly very intense and excessive convective rainfall as well as some strong to severe winds gusts. High PWAT values (morning soundings reveal values above 45mm) suggest that local flash floods will be possible. Some hail will also be possible especially along the front itself, while large hail is rather unlikely to occur. A brief tornado or two cannot be excluded around the NE Adriatic where LLS shear will be maximized.
Storms should cluster into a larger convective system/MCS in the evening hours, slowly moving SE-wards across western Slovenia and NW Croatia overnight. Therefore, an enhanced threat for flash flooding will exist.
... southern and eastern Germany, western Poland, Czech Republic and northern Austria ...
Activity over these areas will be aligned to the main cold front crossing the region. With very cold mid-levels, steep lapse rates will yield several hundreds of MLCAPE overlaping with strong shear. The main threat will be strong to severe wind gusts, while a few tornadoes/funnels are possible given the strong LL shear in place as well.
Quite steep LL lapse rates under the core of the upper low/trough could produce a few waterspouts around the North Sea and Denmark as well.
... areas from northern Balkans into NE Europe and NW Russia ...
A surface low moves into NE Russia with a weakening cold front shifting NE across the NE Europe into western Russia. Healthy BL moisture combined with moderate shear/SREH should overlap with several hundreds J/kg of instability and organized storms will be possible. Threat for strong winds, a few tornadoes and large hail will exist. High PWAT values suggest intense rain threat as well with any organized storm.
... parts of N Marocco and Algeria ...
With a weak termal low forming over Marocco, storms are expected to take place around the peak heating hours, initiated near the Atlas mointains. Very steep lapse rates and moderate instability suggest that threat for large hail and some severe wind gusts will be possible with any storm. Storms should diminish after sunset.
