CONVECTIVE FORECAST
VALID 06Z THU 16/09 - 06Z FRI 17/09 2004
ISSUED: 15/09 12:51Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across central Mediterranean

General thunderstorms are forecast across central Mediterranean and Balkans, southern Baltic Sea, eastern Scandinavia, western Russia, extremely northwestern Europe

SYNOPSIS

Relatively sharp upper trough from Scandinavia to Iberian Peninsula and long-wave ridges over northeastern Atlantic/eastern Europe will propagate eastward during the forecast period ... while southern part of mentioned trough cuts off into western Mediterranean. As the northern part of the troughs moves into eastern Europe ... upper ridge will reach from Iberian Peninsula to western Scandinavia on early Friday east of intense upper long-wave trough over the Atlantic. At lower levels ... warm and unstable airmass over the central Mediterranean will remain east of the cut-off low ... while cold airmass spreads into eastern Europe.

DISCUSSION

...Central Mediterranean ...
Warm airmass is present over the Mediterranean east of a cold front that is expected from Majorca to northern Italy on Thursday, 06 UTC. This airmass is characterized by steep lapse rates above 900 hPa and rather rich low-level moisture ... leading to CAPE in the order of 1500 J/kg as forecast by latest GFS model output. On Thursday ... instability should remain over the region ... while cold front will propagate eastward. Downstream of this cold front ... models suggests quite strong vertical wind shear east and north of a surface low west of central Italy ... and deep layer wind shear should likely reach 25 m/s due to GFS. In the range of the upper trough ... thunderstorms are likely as synoptic forcing due to DCVA and weak WAA is expected ... and convective activity of Wednesday/Thursday night should go on during Thursday over northern Mediterranean. As vertical wind shear will support organized convection ... one or two MCS are expected in the morning hours over Italy/Adriatic moving eastward into western Balkans. Intense rain should be the main threat with this convection ... as well as a tornado or two due to low LCL heights and locally enhanced low-level SRH values. During the day ... a vort-max/jet streak is expected east of the cut-off over central Mediterranean ... and rather strong synoptic forcing should support deep convection over central/southern Mediterranean. Increasing deep vertical wind shear over the central Mediterranean should lead to sufficient SRH for some supercells capable of producing large hail and damaging wind gusts as well as a few tornadoes. Thunderstorms should quickly merge into one or two linear MCS moving ESE-ward. Severe winds and intense rain will become the main threat. Embedded supercells may be capable of producing isolated large hail and a tornado or two.

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