CONVECTIVE FORECAST
VALID 09Z SUN 22/08 - 06Z MON 23/08 2004
ISSUED: 22/08 09:20Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across western Ukaine, eastern Belarus, SWrn Russia

General thunderstorms are forecast across eastern Europe, SWrn Great Britain, Ireland, NWrn France

SYNOPSIS

Western European weak amplified long-wave ridge moves eastward, as NErn Atlantic upper trough rebuilds. Over eastern Europe ... intense short-wave trough moves eastward reaching the Black Sea at the end of the forecast period. At lower levels ... cold and stable airmass has entered the forecast region west of a frontal boundary reaching from NWrn Russia to Greece.

DISCUSSION

...Eastern Europe ...
Well defined frontal boundary exists over eastern Europe. To the east ... warm or very warm airmass is present. Latest soundings show mid-level steep lapse rates from northern Balkans to western Russia ... while low-level airmass is characterized by rich low-level moisture ... yielding CAPE up to 1000 J/kg at 00Z (33345 Kyiv). On Sunday ... surface low ATTM over eastern Balkans is forecast to move NNE-ward along the frontal boundary ... and is expected over extremely western Russia on Monday, 00Z. In the warm sector ... moderate instability will likely build ... and CAPE in the order of 1500 J/kg is expected. In the range of the surface low ... deep vertical wind shear is forecast to reach 20+ m/s underneath the southerly upper jet ... and SRH should be enhanced especially near the center of the surface low. During the next hours ... upper vort-max will move NE-ward into eastern Balkans, western Ukraine, Belarus, and western Russia ... yielding DCVA and QG UVM east of the surface low due to WAA. Thunderstorms have already formed along the cold front over western Ukraine and Belarus and are expected to move NNE-ward. Given synoptic forcing, moderate instability and moderate deep vertical wind shear ... organized thunderstorms are likely capable of producing large hail, damaging wind gusts and a few tornadoes, especially near the center of the surface low where low-level vertical wind shear will be strongest and LCL heights will be lowest. Large surface pressure gradient is present west of the frontal boundary ... and widespread strong wind gusts are expected along the cold front. If an MCS will form along the cold front ... there is a chance that widespread severe wind gusts will affect the region associated with bow echoes. Latest model output supports this scenario over western Ukraine, Belarus, and western Russia. A MDT RISK will be warrant if this scenario materializes.

...Spain...
Latest soundings show well-mixed mid-levels (10K/1000m) from 800 to 500 hPa over southern Spain. Underneath a strong cap ... low-level moisture has increased and CAPE up to 1000 J/kg is expected during the day. Large CIN should inhibit deep convection. However ... model output suggests a weak vort-max reaching the Iberian Peninsula during the day ... and isolated thunderstorms are not ruled out. Given moderate deep-layer wind shear ... supercells are possible capable of producing isolated large hail. There is also a chance of throng downbursts given high LCL and well mixed boundary layer.

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