Storm Forecast
Valid: Sat 04 Mar 2017 06:00 to Sun 05 Mar 2017 06:00 UTC
Issued: Sat 04 Mar 2017 01:29
Forecaster: TASZAREK

A level 1 was issued for S Portugal and SW Spain mainly for severe wind gusts and in lesser extent for excessive precipitation and tornadoes.

A level 1 was issued for Alps and N Italy mainly for excessive precipitation and in lesser extent for large hail and severe wind gusts.

A level 1 was issued for N Adriatic coast mainly for severe wind gusts and in lesser extent for tornadoes.

SYNOPSIS

Large long-wave travels trough W Europe with axis stretching from British Isles up to S France. It is encircled by relatively strong jet on its SW edge and broad area of upper-level divergent flow over France. Secondary shortwave trough travels through N Italy, Switzerland and S Germany. Shallow trough under the strong jet passes also through SW Iberian Peninsula in the morning hours. Convective activity is unlikely in SE and E Europe covered by a broad ridge.

DISCUSSION

...W France...

Steep lapse rates (> 7 K/km) develop in the cold sector and along with 5-6 g/kg MIXR result in a CAPE of around 300-500 J/kg. CI is supported by the strong PVA from the west. Most of the convective cells will remain low-topped with relatively weak updrafts but due to ELs dropping below -20C lightning activity is likely. Thunderstorms will remain mostly in the weak deep and mid level shear environment, thus limiting severe weather threat, but thanks to locally enhanced LLS (> 10 m/s) and SRH (> 100 m2/s2) values in SW France, a small risk for severe wind gusts and tornadoes exist in the afternoon hours.

...SW Iberian Peninsula...

A passage of the shallow low in the morning hours brings tongue of 8-9 g/kg MIXR from Atlantic and develops CAPE up to 100-300 J/kg. Due to strong dynamics (850 hPa wind ~ 30 m/s, large shear and helicity), low-topped supercells capable of producing severe wind gusts and in lesser extent tornadoes cannot be ruled out. However, since no decent QG-lift is available and instability is low/marginal, severe weather potential seems to be limited.

...Alps, N Italy...

Lapse rates exceeding 7 K/km and 5-6 g/kg MIXR develops 300-500 J/kg CAPE in the afternoon hours within a passage of the shortwave trough. Thanks to DLS exceeding 20-25 m/s and strong QG-lift (sharp edge of PVA from west), low-topped supercells capable of producing large hail up to 2 cm (low 0C isotherm) and severe wind gust are possible. Enhanced by orographic lift convective precipitation superimposing with large-scale precipitation may locally result in an excessive precipitation - rain in lower and snow in upper parts of the mountains.

...N Adriatic...

Thanks to moderate PVA, WAA and orographic lift, low-topped thunderstorms may develop in the late afternoon hours along N Adriatic coast. Lobes of enhanced 7 K/km lapse rates overlapping with 7-8 g/kg MIXR produces thin CAPE up to 200-400 J/kg. High shear (MLS ~ 15-20 m/s) and helicity (SRH3km ~ 200-300 m2/s2) may contribute to few supercells capable of producing severe wind gusts and in lesser extent tornadoes, although low CAPE seems to be the main limiting factor for the occurrence of severe weather.