CONVECTIVE FORECAST
VALID Mon 04 Jul 06:00 - Tue 05 Jul 06:00 2005 (UTC)
ISSUED: 04 Jul 01:08 (UTC)
FORECASTER: GROENEMEIJER

There is a slight risk of severe thunderstorms forecast across southern, central, western and northwestern Germany, the eastern Benelux, extreme northeastern France.

There is a slight risk of severe thunderstorms forecast across northeastern Spain

SYNOPSIS

Monday at 06 UTC... a negatively tilted trough along a line from Wales to southwestern France moves northeastward. Ahead of the trough, a deeping surface cyclone is expected over the southern North Sea. A strong southerly flow is expected east of the system's cold front, that should be near a line from the central Netherlands to Toulouse. Over southeastern Europe...a closed low at mid-levels centered over the Bosporus is expected to move gradually eastward.

DISCUSSION

...eastern Netherlands, northwestern Germany...
A 400-800 J/kg of slightly elevated CAPE are expected to be present near the surface low - over the southern North Sea and western Benelux - where widespread convection should be ongoing. East of the cold front, instablity will likely become surface-based during the late morning. Some surface-based convection is expected to develop ahead or along the front as it accelerates eastward during the late morning and afternoon. A few rotating updrafts may form as shear is expected to be strong and storm-relative helicity of about 100-200 m2/s2 should be available to any surface-based right-moving storm. Strong winds and some large hail are likely. An isolated tornado is possible as well given very low LCL heights.

...central and southern Germany, eastern Belgium, Luxembourg...
Ahead of the aformentioned cold front 500-1000 J/kg 50hPa-MLCAPE should be in place in most areas. About 15 m/s deep-layer shear is expected near and ahead of the front so that well-organized storms are expected to form. Some storms may initially be supercells, but rapid clustering is expected. As large cold pools form, the convection may well accelerate eastward or northeastward as one or more bowing MCS's. Those systems will have the capability of producing damaging winds. Additionally, there will be some threat of large hail tomorrow. Presently, the rather modest instability precludes the issuance of a higher than slight risk category.

...eastern Spain, western Mediterranean ...
Around 1000 J/kg 50hPa-MLCAPE and rather strong 20-25 m/s deep layer shear are expected across the indicated area. Forcing for upward vertical motion is expected ahead of a shortwave that reaches central Spain at 15 UTC from the west. Convective initiation is expected across northeastern Spain during the afternoon. The resulting storms may well become supercells with a threat of producing large hail and strong winds. It is possible that storms will form further south as well.

...extreme eastern Bulgaria, northwestern Turkey...
Under the mid/upper low, steep low-level lapse rates, low LCL and LFc heights, and ample vertical vorticity are expected to create a favourable setting for weak tornadoes (landspouts) and waterspouts.

...England...
Low LCL and LFC heights are expected here as well and ample vertical vorticity on the eastern flank of the low over the North Sea create a favourable setting for weak tornadoes (landspouts) and waterspouts.

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