Storm Forecast
Valid: Thu 06 Aug 2009 06:00 to Fri 07 Aug 2009 06:00 UTC
Issued: Wed 05 Aug 2009 21:56
Forecaster: GATZEN

A level 1 was issued for western Turkey mainly for very large hail.

A level 1 was issued for France and northern Spain mainly for large hail and severe wind gusts.

SYNOPSIS

A subtropical ridge extends from northern Africa to Scandinavia, where a surface pressure high is present. Low geopotential over eastern Europe yields a rather strong upper-level jet over the east Mediterranean. Over western Europe, another strong jet is forecast.

DISCUSSION

Western Turkey

At the southern flank of the east European low, a mid-level short-wave trough spreads into western Turkey during the day. This will be associated with increasing mid-level south-westerly winds and weak south-easterly winds at the 700 hPa level, where steep lapse rates will likely spread north-westward. In the boundary layer, the centre of the low is located to the east, while northerly winds evolve over western Turkey. This will be associated with moisture advection from the Black Sea, and diurnal heating will likely result in CAPE in the order of 1500 J/kg.

Given upslope flow and increasing QG forcing during the day, initiation is forecast. Storm that form will likely organize given rather favourably veering profiles, and supercells are not ruled out. These storms are forecast to produce very large hail. Severe wind gusts are also possible. Storms will likely weaken after sunset, while the activity may spread northward where CIN is expected to be weaker.

France

A strong southerly jet west of Europe slowly propagates eastward during the period. Ahead of this trough, warm air mass is present from the Iberian Peninsula to France. At lower levels, a cold front is expected to move into western France in the afternoon hours. Some moisture convergence is expected in the range of this front, and CAPE will likely build due to rather steep lapse rates.

Initiation becomes likely in the afternoon hours over northern Spain and southern France in the range of a weak trough axis moving north-eastward that provides some lift. Additionally, low-level convergence is likely to the north of the Pyrenees. Storms that form will profit of increasing deep layer vertical wind shear and large hail is forecast. Locally severe wind gusts are also not ruled out. Convection will likely spread across western and central France in the evening hours as the trough moves on. Weakening dynamics as well as low-level stabilization are expected to limit severe potential after sunset.