CONVECTIVE FORECAST
VALID 06Z MON 12/01 - 06Z TUE 13/01 2004
ISSUED: 12/01 01:31Z
FORECASTER: GROENEMEIJER

General thunderstorms are forecast across a part of Ireland and Great-Britain and the eastern Mediterranean.

SYNOPSIS

A strong west to westsouthwesterly jet is present over the Atlantic Ocean. A small positive vorticity anomaly is expected to develop into a small low pressure system quite rapidly, that is forecast to move eastward over southern England into the southern BeNelux Monday morning. We will refer to this feature as the first system.

Satellite imagery shows a developing comma indicating a vorticity maximum further to the west (near 50N 33W at 01 Z) which has not been correctly analysed by numerical models. The evolution of this system, that is located well north of the jet is quite uncertain. However, it is well possible that it develops into a intense surface cyclone that may affect the western British Isles perhaps as early as Monday evening. We will refer to this system as the second system.

DISCUSSION

...Ireland and Great-Britain...
Most likely scenario seems to be that the second system will move into Ireland late Monday evening. An unstable air-mass is expected on the western and southwestern flanks of the system. A few thunderstorms may well form there that could bring severe weather. However, as the evolution of the system is uncertain at this time, we will refrain from issuing a categorical risk at this moment.

...Northern France, the Low Countries and west-central and central Germany....
Indications are that the atmosphere near the first system could become unstable in a shallow layer near or just south of the system's centre. Non-convective severe wind gusts are expected to occur in the same area. There is a chance that quite shallow - possibly non-thundering - convection (up to 700 - 500 hPa) will form that could be capable of producing gusts in excess of 65 knots. However, there is quite some uncertainty as to whether this will happen. Therefore, the area that is potentially affected is not included in a categorical risk. An upgrade to slight risk could be needed if additional data supports the development of convection with the system.

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