Storm Forecast
Valid: Fri 29 Aug 2008 06:00 to Sat 30 Aug 2008 06:00 UTC
Issued: Thu 28 Aug 2008 13:44
Forecaster: TUSCHY

SYNOPSIS

Intense depression south of Iceland backs ridging over parts of W-Europe resulting in warm and stable conditions. A progressive upper trough over NE Europe brings cooler air southwards. A disturbance enters SW Europe during the day , increasing thunderstorm chances. The rest of the Mediterranean remains stable.

DISCUSSION

... Spain and Portugal ...

A hot airmass covers those areas with readings of more than 20°C at 850hPa. Approaching disturbance will bring enough lift and a slight cool down to Portugal and NW Spain and this also reflects the thunderstorm spreading, increasing from SE to NW. Modest DLS (around 15m/s) and strong veering overlap with 500-locally more than 1000 J/kg MLCAPE and there will be the risk of large hail with each thunderstorm. Maximized risk should be over NW Spain/N-Portugal and a significant hail report can't be ruled out. GFS proposes rapid clustering during the night hours with enduring thunderstorm activity.

Thunderstorm coverage over central/S Spain will be more sporadic as forcing is weaker/capping stronger, but there are persistent LL deep convergence signals and a few orographic storms are likely. We therefore expanded the highlighted area well SE-wards. Large hail/strong downbursts remain the main risk, but too sporadic for issuing a risk level.

...Highlighted area over E-Europe ...

A tongue of rich BL moisture and modest lapse rates result in a build-up of a few hundreds J/kg instability ahead of the eastward moving cold front during the afternoon and evening hours. DLS and LL shear are enhanced and rapid storm organisation is anticipated. The level-1 contains an isolated large hail/tornado threat. Thunderstorm activity and strength will diminish after sunset.