Storm Forecast
Valid: Fri 10 Aug 2012 06:00 to Sat 11 Aug 2012 06:00 UTC
Issued: Thu 09 Aug 2012 19:49
Forecaster: TUSCHY

SYNOPSIS

Strong ridging covers W-Europe with an extensive surface high pressure area over most of W/C Europe. An upper trough is situated over NE Europe with numerous disturbances rotating around its periphery. A very hot air mass still affects most parts of the Iberian Peninsula, where surface temperatures exceed 40 °C in many places.

DISCUSSION

... Spain ...

An outstanding heat wave continues over Spain with 850 hPa temperatures soaring into the upper twenties/lower thirties. On the mesoscale, an inland moving coastal front separates an humid air mass (dewpoints in the lower twenties) behind the front from very hot and dry air ahead (temperatures in excess of 40 °C with dewpoints in the lower single digits). The frontal circulation of the coastal front will be way too weak to overcome the impressive cap (not even Cu fields were present yesterday), so the focus remains the higher terrain. Very deep EML with mid-level lapse rates locally in excess of 9.5 K/km assists in elevated CAPE of 500-1000 J/kg. However, ridge axis now centered just atop Spain with warmer mid-levels may keep mountain convection even more sporadic compared to yesterday. The main risk will be either dry thunderstorm activity (fires, ignited by lightning) or precipitating storms with a few strong downburst events. We issued a 15-% lightning area for those regions, where confidence in sporadic CI was the highest.

The W-Pyrenees have to be monitored for sporadic CI late in the forecast with rapidly steepening lapse rates and weak disturbances moving in from the west, inserting some mid-level lift. I'll go against models and place a low-end lightning area over that part of Spain, as the environment seems to be supportive for one or two storms. If a storm evolves, wind and hail would be the main hazard.

...The rest of the lightning areas ...

Mainly sub-severe thunderstorm activity is expected for the rest of Europe with marginal hail and strong wind gusts. Isolated large hail may occur over NW-Ukraine/S-Belarus (stronger shear) and heavy rain is possible over Lithuania (slow storm motion) - however no level 1 criterion is expected. Overall storm coverage decreases after sunset despite SE Europe and the Mediterranean. Also, sporadic storms may occur during the night over E-Germany, W-Poland into the Czech Republic as a well structured vorticity maximum moves in from the north.