Europe: ESTOFEX Storm Forecast: Level 1 for parts of France, Benelux, Germany, Italy and Iberia valid until 241013 0600Z. Tornadoes, Heavy rain and hail possible – 231013 1348z

Storm Forecast

Storm Forecast
Valid: Wed 23 Oct 2013 06:00 to Thu 24 Oct 2013 06:00 UTC
Issued: Tue 22 Oct 2013 21:15
Forecaster: PUCIK

A level 1 was issued for Central France, BENELUX and Northwestern Germany mainly for tornadoes and severe wind gusts.

A level 1 was issued for Southern France and Northern Italy mainly for excessive precipitation and tornadoes.

A level 1 was issued for Western Iberia mainly for excessive precipitation.

SYNOPSIS

General macrosynoptic pattern will remain more or less the same as during the previous days – a broad southwesterly flow is forecast over much of Western and Central Europe situated between deep trough over the Atlantic and ridge over Eastern Europe. This trough will translate towards northeast, slightly de-amplifying the ridge but no major reconfiguration is expected. Unseasonably warm airmass has spread all the way up to Southern Scandinavia, while a weak CAA is expected behind the insignificant cold front that will move from France towards Germany. Another significant trough will approach the Iberian penninsula towards the Thursday morning hours.

DISCUSSION

… Central, NE France, BENELUX, NW Germany …

With cooler, moist airmass overspreading the region, low LCLs are forecast. Only moderately steep mid-level lapse rates will very likely limit the instability build-up, so that only few hundreds J/kg of CAPE are expected at best. Strong, unidirectional wind shear is simulated, with much of the shear within the lowest 1 km, yielding LLS values between 10-15 m/s in the region. With the belt of enhanced PV approaching the area, scattered DMC will initiate. In the strong shear regime, low-topped supercells are well possible, capable of severe wind gusts, tornadoes or some mostly sub-severe hail.

… S France, N / NW Italy ….

In the strong southwesterly flow, a belt of steep mid-level lapse rates is forecast to advect over the Mediterranean Sea along with moist low-level airmass. Moist flow experiencing uplift near the coastline or near the Alps will likely initiate widespread DMC – possibly featuring one or more MCS. In case of the training pattern, moist conditions might enhance precipitation efficiency and locally excessive rainfall is expected. Threat will shift from Southern France towards Northern Italy. MCS will likely start building southwards towards the unstable airmass during the Wednesday night hours. Enhanced low level shear near the coastline along with low cloud bases also point at the elevated tornado risk in the region, albeit this threat should be less prominent than the precipitation risk.

… W Iberia …

During the late afternoon / evening hours, tongue of moist and unstable airmass ahead of the trough is expected to initiate widespread DMC near the coastline. With strong low level convergence and enhanced mixing ratios, isolated excessive precipitation event is quite possible. Tornadoes can not be ruled out in this setup with stronger low level shear inland, albeit CAPE here will be likely mostly elevated, thus possibly rendering this shear ineffective.

Related:

Severe Weather Warnings for Europe. Orange Alerts for Switzerland, France, Italy and Netherlands http://www.meteoalarm.eu

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