Storm Forecast
Valid: Mon 14 Jun 2010 06:00 to Tue 15 Jun 2010 06:00 UTC
Issued: Sun 13 Jun 2010 21:42
Forecaster: GROENEMEIJER

A level 2 was issued for much of the Pannonian Plain, eastern Slovakia, NW Romania, western Ukraine, SE Poland, and southern Belarus for large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for areas surrounding the level 2 area including larger parts of Poland, Belarus, the Ukraine, Moldova and Romania and across a larger part of the southern and western Balkans, Slovenia and eastern Austria for large hail, severe wind gusts and excessive rainfall.

A level 1 was issued for parts of the Western Mediterranean, including northern Algeria, and northwest Tunisia, mainly for large hail and excessive precipitation.

A level 1 was issued for parts of Turkey mainly for large hail.

A level 1 was issued for parts of France mainly for (weak) tornadoes.

SYNOPSIS

Within a longwave trough over western Europe, three distinct vorticity maxima are present. Once such system, over Morocco lifts NEward during the forecast period. Another, initially over Britain, moves southward. A frontal zone on its southereastern fringe is located from northern Algeria across Italy to the Pannonian Plain and into the northern Ukraine. Across the Balkans, a warm and very humid low-level air-mass has formed. A weak vorticity maximum over Hungary triggers widespread convection in the moist are as a frontal wave develops that arrives in Belarus on Tuesday morning

DISCUSSION

Pannonian Plain, Balkans, Slovakia, Poland, Ukraine, Belarus....

A zone of warm and unusually moist air has developed over southern Parts of the Pannonian Plain (i.e. E Croatia, Serbia, W Romania, with reported surface dew points mostly in the 20-25 C range at sunset on Sunday. This resulted in MLCAPE values exceeding 3000 J/kg in these areas. A 5-10 m/s southerly low-level flow within the developing frontal wave will advect this moist air a bit further north across much of the level 2 area.

On Monday morning, scattered thunderstorms are expected to be ongoing across the Czech republic, Austria and across western parts of the Plain across Slovenia, Hungary, Slovakia. These should increase in coverage in response to diurnal heating ahead of a cold front that moves into the area from the northwest. With extremely high MLCAPE values around 3000 J/kg expected across much of the level 2 area, and moderate deep-layer shear of around 15 m/s, some supercells are expected in addtion to powerful multicell systems. These will bring a threat of very large hail, possibly in excess of 5 cm in some places, and powerful downbursts.

Some storms will likely cluster during the afternoon and evening and move east to northeastward in the form of an MCS producing severe wind gusts in a zone from SE Poland through Belarus. Model guidance shows the development of very intense MCSs across Belarus, which implies a threat of excessive rainfall as well.

Across Serbia and Romania, the coverage of storms is more questionable because of the lack of a clear trigger mechanism. However some storms will probably form. Any storm will do so in an environment of extreme instability with CAPE values around or above 3000 J/kg and 15-20 m/s deep-layer shear. Such storms will be capable of producing very large hail, severe downbursts and flash floods.


Western Mediterranean, including northern Algeria, NW Tunisia and Sardinia...

A vort max across Morocco will lift NEward across NW Algeria into the Western Mediterranean. the associated forcing is expected to help initiate storms across the Tell Atlas, that subsequently move over the Mediterranean. Overnight they may affect Sardnia as well. Given that the storms occur in strong shear and with abundant MUCAPE, they should be capable of producing large hail.


Turkey...

QG lift ahead of a trough moving onto the Anatolian peninsula from the south, should produce sufficient forcing for scattered thudnerstorms to develop. Steep lapse rates will render the storms capable of producing large hail in spite of the near-absence of vertical wind shear.


France...

A cold-core low that moves southward over western France is expected to create a low-level convergence zone with high vertical vorticity, along which deep convection should occur in an environment of steep low-level lapse rates. This combined with a low LCL height may allow a couple of non-mesocyclonic tornadoes to occur primarily during the afternoon.