Storm Forecast
Valid: Tue 18 Jul 2006 06:00 to Wed 19 Jul 2006 06:00 UTC
Issued: Tue 18 Jul 2006 10:43
Forecaster: VAN DER VELDE

SYNOPSIS

A large blocking high over Europe is nudged between two longwave upper troughs, one over the Atlantic near Portugal, the other one over northern Scandinavia into Russia.
The latter is a very dynamically strong system and an unstable, highly sheared airmass is present at the right entrance of the jet and vorticity maximum, and is expected to produce widespread severe weather.

DISCUSSION

...Northern Russia...

A cold front plows into an unstable airmass. 00Z soundings in the region have shown very strong midlevel winds (>20 m/s), veering with height in the lower levels, creating favourable conditions for well-organised convection. Supercells are possible, but the main mode will be a squall line with bow echoes, producing widespread damaging winds. Large hail and a tornado are possible as well, the latter especially if low-level (0-1 km) shear manages to get over about 10 m/s.
[Note: area has been drawn a bit too westwards]

...southern Turkey...

00Z sounding east of our map shows good instability and shear conditions, and may be conducive for large hail. GFS and MM5 don't produce precipitation though.

...Spain, Portugal...

Moderate shear conditions are present in 00Z soundings and in the GFS model. As the upper trough comes closer to the European mainland, upper winds increase over this area and a thermal surface low pressure area will start to develop and walk northwards. Given deep dry boundary layers and midlevels, storms have the capability of producing severe outflow winds. Some large hail is also likely.
Minimal shear and lift conditions over France should limit potential of severe weather there, although an isolated large hail, gust, or landspout is not unthinkable.