Storm Forecast
Valid: Mon 04 May 2020 06:00 to Tue 05 May 2020 06:00 UTC
Issued: Mon 04 May 2020 04:00
Forecaster: VAN DER VELDE

A level 2 was issued across N Spain and SW France mainly for severe convective wind gusts, large hail and tornadoes.

SYNOPSIS / DISCUSSION

High pressure dominates across British Isles and Benelux, while a cold front belonging to a Scandinavian/Baltic low can trigger some thunderstorms in central Europe. Lows with unstable airmass are also active around Ukraine and Turkey. The more dynamic system is a large Atlantic low west of the Iberian Peninsula, which created a Spanish Plume with steep lapse rates from low to mid levels, drifting northward over Bay of Biscay and SW France. A shortwave mid/upper trough enters Portugal at 12Z, affecting northern Spain during the afternoon and Bay of Biscay and France during late evening and night. The main models ECMWF, ARPEGE, ICON and GFS calculate several hundreds J/kg CAPE (over 1000 MUCAPE over SW France, but capped/large CIN), a relatively high LCL (1500-2000 m) and massive vertical wind shear (30-50 m/s 0-6 km, 25 m/s 0-3 km, 10-15 m/s 0-1 km, 250-500 m2/s2 0-3 km SREH). The mean wind at 1-3 km altitude over 20 m/s suggests potential for widespread severe gusts. The aforementioned parameters support strong downburst, large hail and perhaps an isolated tornado. The largest complex is placed in most models over the central/eastern Bay of Biscay, but south and eastward are drier such that model precipitation may not reach ground. GFS deep convergence and uncapped parcel patterns suggest a wider area of storm initiations. A level 2 is issued mainly for probability of a wide extent of severe gusts and large hail.