CONVECTIVE FORECAST
VALID 06Z THU 08/01 - 06Z FRI 09/01 2004
ISSUED: 07/01 18:08Z
FORECASTER: GATZEN

General thunderstorms are forecast across NWRN Europe

SYNOPSIS

Two intense long-wave troughs are present oder the NERN Atlantic and the SERN portions of Europe. Both systems will propagate eastward. Over WRN Europe ... sharp upper ridge will weaken while moving eastward. During the FCST period ... negatively tilted short-wave trough will cross Great Britain. Upstream of this feature ... the very strong (more than 80 kts@300 hPa) N Atlantic jet will expand into WRN Europe.

DISCUSSION

...Northwestern Europe ...
Negatively tilted short-wave trough will cross Great Britain during the FCST period. Associated DCVA and weak WAA are FCST downstream of this feature, yielding strong UVM over the central and NRN portions of Great Britain. Latest satellite image shows stratiform clouds within the WAA regime and soundings suggest that this airmass should be rather stable. In the range of the trough ... polar airmass will enter the forecast region west of a cold front. Satellite images show enhanced CBs over the Atlantic indicating that this airmass should be convectively mixed. During the FCST period ... DCVA is expected as the strong jet stream expands northward. Embedded short waves may cause rather strong UVM and convective activity is expected that should spread into SRN and CTRL Great Britain and NWRN France reaching NRN Great Britain and Benelux/extremly WRN Germany at the end of the forecast period. Low-level helicity seems to be relatively weak underneath the trough axis and west of it, and an enhanced potential of organized severe thunderstorms is not forecast. Severe wind gusts are expected with thunderstorms due to the strong surface pressure gradient, though. Additionally ... orographically enhanced helicity may support shallow mesocyclones that could produce brief tornadoes and small hail. Nevertheless latest GFS output suggests the formation of a comma cloud west of Great Britain that could reach the forecast region at the end of the forecast period. If a comma cloud may form tomorrow ... an update will be needed as widespread severe weather will be possible. Severe wind gusts should be the main severe threat if this scenario becomes true.

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