Forecast Update
Valid: Sun 04 Mar 2007 17:00 to Mon 05 Mar 2007 06:00 UTC
Issued: Sun 04 Mar 2007 17:00
Forecaster: TUSCHY

SYNOPSIS

Please refer to the outlook issued at Sat 03 Mar 2007 17:39 UTC !

DISCUSSION

...SE Romania and parts of Bulgaria...

A few thunderstorms developed during the past few hours in a weakly sheared environment. 12Z LRBS indicated very steep LL lapse rates with 100-200 J/kg instability release.
Storm mode should have been a pulsating single cell - mode with a few strong wind gusts possible given pretty dry PBL.
Surface heating has already reached its maximum and a constant cool down of the lower levels will support a rapid decrease in thunderstorm activity during the next few hours, therefore won't expand the thunderstorm area towards the north.


...France...

An impressive warm-up occured over extreme SW France, where in conjunction with foehny conditions temperatures reached 27-28°C at 15Z north of the Pyrenees
The T-Td spread over most parts of SW France is pretty high with up to 10°C and very warm temperatures between 900 - 800 hPa will support capping conditions during the next few hours.
An isolated thunderstorm evolution can be expected at 20Z and onwards, when surface will cool down, the thermodynamic profile at low-/ mid-levels will become more favorable and strong forcing will reach W-France.
Additionally, a dry slot will cross extreme W / NW France from the SW ( 21Z onwards ) and potential instability release could be supportive for scattered storms to develop.

I still went pretty far inland with the general thunderstorm area, because topography and eastward shifting, tight thermal gradient could be the focus for an isolated thunderstorm evolution well towards the east.

Limited instability release and expected low-topped thunderstorm evolution preclude a level-1 although shear would be pretty strong.
An isolated severe wind gust report and marginal hail will be possible with each stronger cell.

... Coastal areas surrounding the English Channel and coastal areas of W-UK....

NE-ward shifting upper-level trough with very cold mid-level temperatures will cross those areas between 22Z-06Z.
Models indicate some low-end instability release and scattered showers / thunderstorms can be expected.
In fact, 16Z IR image already showed a broad Cu-field of cooling cloud tops S / SW of Ireland.
A level-1 looks reasonable regarding a moderately enhanced tornado potential along the coastal areas, where instability and strong LL shear overlap and LCLs stay low, too.