Storm Forecast
Valid: Mon 10 Aug 2020 06:00 to Tue 11 Aug 2020 06:00 UTC
Issued: Mon 10 Aug 2020 05:35
Forecaster: VAN DER VELDE

A level 1 was issued across central Germany, Czech Rep. Slovakia, Romania mainly for excessive convective precipitation.

A level 1 was issued across Netherlands and NW Germany mainly for severe convective wind gusts and large hail.

A level 1 was issued across W France and Spain mainly for large hail and severe convective wind gusts.

A level 1 was issued across the UK mainly for severe wind gusts and tornado chances.

A level 1 was issued for the eastern Black Sea area mainly for excessive convective rainfall.


DISCUSSION

One of few Spanish Plume situations of this summer has finally installed across western Europe again. The steep low-mid level lapses are found from N Africa across Spain, France and UK. Also across much of central Europe they are pretty solid. But mixing ratios (dewpoints) remain a bit limiting except across SW France, UK and Netherlands. In general, there is very little dynamic action across Europe which makes convective initiation dependent on orographic features and a few convergence areas.

An anticyclone over Scandinavia causes easterly flow across Poland and Germany, converging W-E line across central Germany, Czech Republic and Carpatian mountain range. Weak vertical shear and slow storm motion with moderate MLCAPE will help excessive rain production. Severe wind gusts are most likely across N Germany, Netherlands (MLCAPE 1500-2000 J/kg, but lack of trigger mechanisms) W France, and UK, where Delta-Theta-E reaches 20 K. Over UK, a wave moves northward, triggering storms which may partly benefit from significant SREH and >10 m/s LLS to produce large hail and tornadoes. However, it depends how well they root into the boundary layer instead of staying elevated.

Over France and Spain, low level air is quite dry which causes high cloud base (LCL) over 2500 m. Over W France the CIN may limit convective development (ECMWF and ICON show limited rainfall) but Spain and later SW France see more influence from shortwave troughs. Spain is weakly capped with inverted-V like soundings with fragile CAPE and cloud base over 2500m, wth moderate (10-15 m/s 0-3 and 0-6 km) wind shear, which likely still allows multicells and perhaps an isolated supercell storm as long as the sun is up, with large hail and severe wind gusts.