CONVECTIVE FORECAST - UPDATE
VALID 15Z THU 22/07 - 06Z FRI 23/07 2004
ISSUED: 22/07 15:46Z
FORECASTER: GATZEN
There is a moderate risk of severe thunderstorms forecast across southwestern and central France
There is a slight risk of severe thunderstorms forecast across western Spain, most of France, southern Benelux, southern Great Britain
General thunderstorms are forecast across Iberian Peninsula, western Czech Republic, Austria, northern Balkans, western Germany, Alpine region, Balkans, Baltic States, eastern Poland, western Belarus, western and eastern Ukraina, western Russia
SYNOPSIS
Upper high geopotential axis is present from Algeria to eastern Alpine region and further to northern Russia ... and broad SW-erly upper flow remains to the west of this ridge axis. Over SE-ern Europe ... upper low-pressure system is centered over SW-ern Russia. During the forecast period ... a short-wave trough will cross Central Europe eastward. Two additional vort-maxima will cross Great Britain and W-ern France. At lower levels ... warm and unstable airmass remains SE of a line from central Iberian Peninsula to the Channel to northern Germany and further to the Baltic States.
DISCUSSION
...Southwestern to central France...
Quite impressive setup seems to form over western and central France. Low-level moisture has improved underneath the cap with dewpoints in the lower 20s degree Celsius, and CAPE has reached up to more than 1800 J/kg according to latest Bordeaux sounding. Approaching short-wave trough should lead to sufficient UVM to break the cap. Vertical wind shear will be favorable for mesocyclones with more than 20 m/s deep layer wind shear and around 200 mē/sē 0-3 km SRH. Developing thunderstorms should quickly become supercells capable of producing very large hail, severe wind gusts and tornadoes. Some tornadoes may be strong. Large cap may be favorable for isolated storms moving eastward before merging into one or two MCSs spreading NEward. Large hail, severe wind gusts and flash flooding should be possible, as well as a few tornadoes.
...Western Spain...
Thunderstorms have developed over western Spain. Quite strong deep layer wind shear may be favorable for supercells. Large hail will be possible. There is also an enhanced threat of severe downbursts due to dry mid-level airmass indicated by latest soundings.
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