CONVECTIVE FORECAST
VALID Mon 13 Jun 06:00 - Tue 14 Jun 06:00 2005 (UTC)
ISSUED: 13 Jun 07:49 (UTC)
FORECASTER: GROENEMEIJER

SYNOPSIS

Monday at 06 UTC... main feature on the weather maps is a vertically-stacked low pressure system over the southern North Sea. An intense shortwave trough is analysed from Schleswig-Holstein to the English Channel. Another shortwave trough just northwest of northwestern Spain is expected to move slowly eastward. South of a frontal zone, approximately along a line from Bordeaux to Prague, a warm air-mass is present. North of a trough extending from the aforementioned low to a low-pressure center north of Kiev, a warm plume is advected northwestward into Finland and northern Norway and Sweden.

DISCUSSION

...France, Spain ...
Thunderstorms are ongoing across central and east-central France, that are probably fed by a layer slightly above the 800 hPa pressure level (per LFLL 00Z sounding). GFS develops widespread convective precipitation across much of northern Spain and southern France in the 12Z-18Z time frame. Around 15 m/s deep-layer shear is forecast across the region, and storms south of the front may become surface-based, suggesting that isolated severe weather events may occur. The highest threat of strong winds will be present across northern Spain, where a 2 to 3 km deep, dry boundary layer should provide opportunity for evaporationally enhanced downbursts. However, a negative for the severe wind threat is that lower tropospheric winds are weaker.

...central, eastern Finland, parts of Russia ...
Within the warm plume that is advected eastward into central Finland, up to 1000 J/kg of SBCAPE will likely form locally. 0-6 km bulk shear is forecast to be in the 10-20 m/s range, which should be favourable for multicell storms. Given that lower tropospheric winds will be rather strong initially, there seems to be some threat of strong wind gusts, although they should generally remain below severe levels (> 25 m/s). At the time of greatest convective activity (early evening), the winds above the boundary layer should have subsided. In addition to the gusts, some large hail may occur as well.

...Denmark, southern Norway, southwestern Sweden...
The intense trough is expected to rotate northward into the area. Ahead of the system, strong forcing for upward vertical motion is expected to destabilise the air-mass sufficiently for thunderstorms to form. Forecast low LCL heights, LFC heights and ample vertical vorticity may allow for a couple of waterspouts to form.

...eastern belarus, north-central Ukraine, adjacent parts of Russia...
Thunderstorms are expected in the neighbourhood of the aforementioned cold upper-level low. Very low LCL anf LFC heights of a couple of 100 meters are forecast, which in combination with ample vertical vorticity may well lead to a few, likely weak, tornadoes.

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