Storm Forecast
Valid: Wed 22 Jul 2020 06:00 to Thu 23 Jul 2020 06:00 UTC
Issued: Tue 21 Jul 2020 19:55
Forecaster: PUCIK

A level 1 was issued across Pyrenees mainly for excessive rainfall.

A level 1 was issued from Massif Central towards the Alpine range and northern Italy mainly for excessive rainfall, large hail and to the lesser extent for severe wind gusts.

A level 1 was issued across Romania mainly for excessive rainfall.

A level 1 was issued across parts of Russia mainly for excessive rainfall.

SYNOPSIS

Prevailing zonal flow is forecast across much of the domain south of the cyclonic vortex centered over Sweden. Q-vectors do not reveal any significant impulses travelling in the strong flow, except for the UK by Thursday morning and a trough over western Russia. Closer to the surface, a quasistationary frontal boundary will stretch from France through the northern Alps into Romania, Ukraine and Russia, curving northwards around the cyclonic flow associated with a deep cyclone centered over Finland. Thunderstorm activity will be confined mostly to the aforementioned frontal boundary.


DISCUSSION

... Pyrenees ...

Scattered to widespread thunderstorms will initiate along the mountains during the day. Forecast soundings show substantial CAPE with wind profiles favouring rather slow moving storms. Excessive rainfall will be the primary threat.

...Massif Central through N Italy, Switzerland into Austria ...

South of the frontal boundary, NWP agrees on considerable lower tropospheric moisture, increasing to over 12 g/kg over southern France and southern Alpine foothills. Combined with lapse rates reaching around 6.5 K/km, MLCAPE values around 1000 J/kg seem likely. Scattered to widespread storms will initiate in the afternoon to evening hours and their cold pools may act as a source of a secondary initiation mechanism over the adjacent lowlands. With DLS reaching 10 - 15 m/s, possibly higher over the southern Alpine foothills, well organised multicells and even some transient supercells are forecast. Stronger cells may be capable of large hail and isolated downbursts. With mountains focusing the initiation of cells, a quasistationary system may develop with attendant heavy rainfall threat.

... Romania ...

Skinny CAPE profiles with lapse rates generally below 6.5 K/km are forecast. The highest likelihood of initiation will be confined to the Carpathian mountain range, but the best moisture will be displaced more to the west. It is plausible that some quasistationary storms will form over the mountains with threat of heavy rainfall with secondary development spreading into lowlands during the late afternoon.

... Russia ...

Forecast soundings show very skinny CAPE profiles with lapse rates barely reaching 6 K/km with low LCLs and high RH through the mid to upper troposphere. While updrafts will likely remain weak, considerable warm cloud depth may foster efficient heavy rainfall processes with a threat of local flooding from more intense cells.