Storm Forecast
Valid: Wed 08 Oct 2014 06:00 to Thu 09 Oct 2014 06:00 UTC
Issued: Tue 07 Oct 2014 20:41
Forecaster: PUCIK
A level 1 was issued for England and Wales mainly for severe wind gusts and tornadoes.
A level 1 was issued for Eastern France mainly for severe wind gusts and to the lesser degree for tornadoes.
A level 1 was issued for Western Iberia mainly for excessive rainfall and to the lesser degree for tornadoes.
SYNOPSIS
A major cyclonic vortex will persist over the Atlantic with several short-wave troughs rotating around its periphery. Generally speaking, much of Europe will be under a WAA with southwesterly flow on the forward flank of the vortex. Towards the east, a ridge will amplify from N Africa towards S Italy and Ukraine. On the other hand, cut-off, slowly filling low will drift from Greece towards S Turkey.
DISCUSSION
... England, Wales ...
NWP is in general agreement with the passage of a short-wave trough over the region between 09 and 15 UTC. Behind the warm front, that is forecast to cross the region in the morning hours, warmer and moister airmass will advect from the south, increasing dewpoint values. Combined with the forcing from the approaching trough, marginal instability is forecast to build-up, possibly featuring a few hundred J/kg of MLCAPE towards 12 UTC. Convection will likely initiate along the cold front advancing from W - SW, with some linear organisation likely. 850 hPa flow is forecast to increase, reaching 20 m/s after 12 UTC. In such configuration, severe wind gusts may occur. Tornado threat will be conditional (especially concerning the isolated storm mode) but will exist given the degree of LLS and LCLs well below 1000 m.
... Eastern France ...
With enhancement of the southerly flow, low-level moisture will advect from the Mediterranean Sea northwards towards the region. Because of the lack of steep lapse rates, degree of latent instability will remain limited, but may be sufficient for low-topped DMC. Given the degree of vertical wind shear and the presence of 20 - 25 m/s 850 hPa flow, convection may be well organised, possibly featuring some linear structures, capable of severe wind gusts. SREH values reaching 300 m2/s2 also point to the threat of tornadoes particularly in case that supercells manage to form.
... Western Iberia ...
To the south of the stalling frontal boundary, a so-called "river of atmospheric moisture" will impinge on the Iberian coastline in the prevailing southwesterly flow. With unstable airmass, featuring CAPE values mostly around 500 J/kg, coastal convergence should aid in the repetitive initiation of DMC and will likely result in the training pattern of cells or several waves of DMC passing over the certain spots. Given high RH profile, low LCLs and abundance of low-level moisture, excessive precipitation will become a distinct threat here. Some locations may see 24 hour rain sums easily exceeding 100 mm. Enhanced LLS especially over the northern part area may support an isolated tornado threat.
