Storm Forecast
Valid: Sat 31 Oct 2009 06:00 to Sun 01 Nov 2009 06:00 UTC
Issued: Fri 30 Oct 2009 23:15
Forecaster: KOROSEC

A level 1 was issued for SW England towards Britanny mainly for severe wind gusts.

SYNOPSIS

Strong ridging over much of Europe persists while a deep trough enters western Europe during the day. Along with this trough, a rapidly deepening surface low with a cold front approaches British Isles by Sunday 06z. An elongated trough over eastern and southeastern Europe becomes more pronounced and a weak surface depression forms over southern Turkey and eastern Mediterranean sea.

DISCUSSION

... SW England towards Britanny ...

As the deep trough digs into the British Isles, a new surface depression forms on its southern edge. Its expected to reach southwestern UK by Sunday morning. Some differences between GFS and ECMWF models exist, where GFS has the low deeper and slightly faster/more to the east than ECMWF. While the convection is limited only the the narrow zone south of triple point, highly sheared environment (25m/s 0-6km shear, above 200m^2/s^2 of SREH in the lowest 3km layer) seems favorable for severe wind gusts along the rapidly moving cold front. Most of the wind gusts should be non-convective, however. A level 1 was issued for SW England area and southwestwards towards Britanny where higher probabilities for a few severe gust events exist. More to the north, quite steep lapse rates behind another low north of UK will overspread the region. Numerous showers should form in the cold airmass, while steep lapse rates could result in a couple hundreds J/kg of MLCAPE and allow some electrified convection as well.

Aegean sea, western Turkey ...

As the trough deepens and approaches during the day, locally heavy rainfalls are expected along the quasi stationary frontal boundary over northern Turkey. Models simulate marginal instability mostly over western Turkey and a few storms are possible which could locally support excessive rainfalls besides the orographic effects. More to the west, over Aegean sea and southern Greece, moderate shear/SREH will exist. But again only weak instability signals preclude any well organized convection. Slightly higher chances for better organized storms seem possible along the coastal southern Turkey, where better instability will be placed. With the cooler mid-levels coming overnight to Sunday, relatively high LL instability is expected over warm waters of Aegean sea. Cold northerly winds should limit most of convection, but if it forms, a couple of waterspouts can occur. However, storms coverage over all areas is too low to warrant a threat level.