Storm Forecast
Valid: Wed 11 Oct 2006 06:00 to Thu 12 Oct 2006 06:00 UTC
Issued: Wed 11 Oct 2006 06:38
Forecaster: GATZEN

SYNOPSIS

Broad high geopotential covers Europe. Weakening negatively tilted trough axis connected to northern Atlantic long-wave trough has reached British Isles and Bay of Biscay. A quite narrow tongue of warm and moist air mass is present ahead of the trough axis from Iberian Peninsula to western France and British Isles. A cold front is forecast to move eastwards into France/North Sea during the day ... and convective activity that started on Tuesday is expected to go on. Another focus of thunderstorms is again Aegean Sea region ... where upper cut-off remains.

DISCUSSION

England

Latest soundings show that unstable air mass is located east of a cold front over western British Isles and Bay of Biscay. This air mass shows steep lapse rates above the boundary layer ... and given rather rich low-level moisture ... CAPE was measured over a broad region. While soundings indicate steep mid-level lapse rates and high CIN over central Fronce in the axis of warm air mass ... CIN is quite weak over Great Britain due to rather cool layers in the range of the approaching rough axis. Actually ... some thunderstorms are present in the range of the warm air mass over England that should go on during in next hours. Given a strong southerly flow ahead of the cold front ... with quite strong veering and high SRH as indicated by latest sounding data ... thunderstorms that root to the boundary-layer will pose a threat of tornadoes given quite moist boundary-layer. Limiting factor is that boundary-layer is rather stable. During the day ... cold front moves into England ... and additional showers and thunderstorms should form. While the trough weakens ... southerly flow is forecast to weaken as well ... and vertical wind shear is expected to become more unfavorable for organized convection ... so threat should gradually weaken during the day.

France, northern Spain, western Mediterranean

In the range of the warm air mass ... CAPE is likely to remain during the day. Approaching trough should lead to some QG forcing ... and a few embedded thunderstorms are expected to form. Rather weak vertical wind shear will be present and severe weather is not likely. To the north-west ... convective activity should intensify along the cold front. Given stronger vertical wind shear in the range of strong upper southerly jet ... thunderstorms are forecast to organize into multicells. Supercells seems to be not likely as veering is forecast to be unfavorable. However ... given rather strong QG forcing ... thunderstorms may merge into an MCS as shown by latest GFS model run. Strong wind gusts should be possible then over northern France during the evening hours. Dependent on the organization of the convection ... an upgrade may be warranted due to the chance of severe wind gusts later on.

Aegean and surrounding areas

In the range of upper cut-off ... unstable air mass remains due to easterly low-level winds. Given slow-moving storms ... locally high precip is possible again. Other severe weather is not likely given weak vertical wind shear.