Storm Forecast
Valid: Fri 16 Aug 2013 06:00 to Sat 17 Aug 2013 06:00 UTC
Issued: Thu 15 Aug 2013 14:33
Forecaster: TUSCHY

A level 1 was issued for NE Spain mainly for large hail, strong to isolated severe downbursts and heavy rain. An isolated tornado event is possible.

SYNOPSIS

Numerous upper level waves affect the northern part of Europe and bring unsettled conditions from the North Sea all the way to Finland. A more robust mid-level warm-up will be underway over Ireland during the overnight hours with the approach of a potent disturbance. An upper low moves from the Ionian Sea towards the Aegean Sea and another weak upper level trough affects the Iberian Peninsula ... offering the best chances for DMC.

DISCUSSION

... NE Spain ...

A weakening upper-level trough approaches N-Spain during the forecast. Attendant minor surface pressure drop assists in a prolonged period with easterly onshore flow towards N-C Spain. A moist air mass is in place east of NE Spain with BL dewpoints in the lower twenties. As this moisture becomes advected beneath 7-8 K/km mid-level lapse rates, 1000 to 2000 J/kg MLCAPE likely evolve. 10-15 m/s DLS will be enough for organized DMC and similar values are forecast temporarily (afternoon/evening hours) in the lowest 3 and 1 km AGL. Expect a rapid upswing in convection between 12-15 Z mainly along the mountains. During the late afternoon and evening hours, this convection moves also off the mountains towards the lower elevations of NE-Spain. During initiation, expect organized multicells and isolated supercells with large hail and strong to severe wind gusts. Betimes, upscale growth into thunderstorm clusters is forecast with heavy rain, strong wind gusts and large hail. With lowering LCLs and enhanced LL shear, an isolated tornado event can't be ruled out. 10-15 kt storm motion vectors and weak forcing indicate slow moving clusters to the E/SE, but think internal dynamics might bring this cluster all the way to the coast. Therefore we expanded the level area further east.

During the night, both, the S-ward sliding forcing and low CIN also allow further convection to fire over C/S/E Spain. Despite modest shear, CAPE remains quite high (around 1000 J/kg ), so a few overnight severe events (large hail, heavy rain and severe downbursts on an isolated scale) can't be ruled out.

... Rest of the lightning areas ...

Daytime driven thunderstorms evolve from S-Italy all the way to Romania. Shear remains very weak, but up to 1000 J/kg MLCAPE still supports a few intense pulse storms with isolated large hail and a localized downburst/heavy rainfall event. Expected coverage remains too marginal for any level area.

Of interest is the augmented LL CAPE over C-Romania, where an isolated tornado event will be possible.

Marginal CAPE and weak shear preclude organized DMC over far NW Russia. A few marginal hail and strong wind gust events may occur over SE Norway and far W-Sweden, where 500 J/kg SBCAPE and 20 m/s DLS overlap.