Storm Forecast
Valid: Mon 07 Sep 2009 06:00 to Tue 08 Sep 2009 06:00 UTC
Issued: Sun 06 Sep 2009 22:40
Forecaster: KOROSEC

No threat levels have been issued.

SYNOPSIS

A large ridge with stable conditions is building over western and centrale Europe, while an upper level low affects SE Europe. The trough over northern Scandinavia moves NE-wards and a few storms could form along the cold front.

A new trough with a developing deep cyclone approaches Ireland with a SW-wards extending cold front. A weak low at mid and upper levels will affect southern Iberia and N Morocco / Algeria.

DISCUSSION

... Iberian peninsula into N Morocco / Algeria ...

Iberian Peninsula will be affected by a weak upper/mid-level low placed north on Marocco. Easterly flow from the western Mediterranean will maintain the LL moisture and some CAPE will develop. In an environment with less than 10 m/s deep layer shear, most storms should move very slowly and may produce heavy rainfall and isolated large hail. A threat level is not warranted as the expected storm coverage is too low. Except for some storms over N Morocco / extreme S Spain / Portugal, most of the convection will be diurnally driven and should diminish after sunset.

... southeastern Europe ...

A short-wave trough now acting as a large upper low will bring another day of convective activity over these areas. Models simulate quite high instability, mostly over the warm waters. Over the western Black sea and eastern Bulgaria a moderate deep-layer shear up to 15m/s should allow storm organization, a few large hail and excessive rainfall events will be possible. More to the south over Aegean Sea and Mediterranean, less shear will be available for organized storms. But according to steep LL lapse rates and high LL CAPE, an isolated waterspout is not ruled out.

... extreme NE Sweden and central Finland ...

Along the cold front crossing these areas, models develop a few hundreds of CAPE near the triple point, scattered showers and thunderstorms could develop. Moderate shear/SREH suggest that cells could gain some organization but as the activity is expected during the night/early morning hours, severe storms are unlikely. Although the probability is not that high, strong wind gusts and perhaps a funnel / brief tornado could be possible.

... coastal areas of western Norway ...

A cold front will affect the Norvegian coast during the daytime when models simulate marginal CAPE in strongly sheared environment. A narrow line of showers and a few thunderstorms may form along the cold front which could be accompanied by strong to marginally severe gusts but overall threat is too low for a level 1.

... Ireland towards W Scotland ...

Another deep trough with a rapidly developing surface cyclona approaches the British Isles in the late evening / night hours. Its cold front will extend southward and most of the rainfall along the front should be stratiform as there is almost no CAPE forecast by GFS and WRF. This region has to be monitored during the day and an update may be issued if conditions are better for organized convection. In this scenario, isolated severe gusts should be the main threat.