Storm Forecast
Valid: Thu 23 Jul 2020 06:00 to Fri 24 Jul 2020 06:00 UTC
Issued: Thu 23 Jul 2020 06:20
Forecaster: GATZEN

A level 1 was issued across northern Spain, southern France, northern Italy, Switzerland, Austria, Slovenia, northern Croatia, Hungary and Romania for excessive rain, large hail, and severe wind gusts.

A level 1 was issued across the northern Balkans for excessive rain and large hail.

A level 1 was issued across the Caucasus mountains for large hail and severe wind gusts.

SYNOPSIS

A quasi-stationary trough is located across NE Europe. Within a zonal mid-level flow, an Atlantic trough moves into western and central Europe today, providing some quasi-geostrophic lift from France into the Alpine region. Additionally, vertical wind shear increases to about 15 m/s ahead of this trough. At lower levels, main feature is a frontal boundary stretching from northern Spain towards the Alps and into the Balkans.

DISCUSSION

Northern Spain and southern France into northern Italy and the Alps

A moist and unstable air mass is present that allows for convection initiation today, especially over mountains where upslope flow is present. Later on, supported by frontogenetic lift that inctreases ahead of the approaching trough, more storms are expected to form from the west, with high coverage of elevated storms across the southern Alps and northern Italy during the night.

Storms can organize in around 15 m/s deep layer vertical wind shear. Multicells are the dominant storm mode, along with some multicells along the slopes of the Alps. These will be capable of large hail. Additionally, local excessive rain and severe wind gusts are forecast. Later in the period, increasing coverage of storms will cause an increasing rain threat. Additionally, due to increasing 0-3 km shear, some brief bowing segments are not ruled out across southern France and northern Italy, with an increased wind threat.

Eastern Alps to northern Balkans

In a weakly sheared,, unstable air mass, thunderstorms are forecast over the mountains today. Main storm mode is single cells and multicells with a threat of excessive rain and locally large hail.

Causasus mountains

In rather moist air mass with steep low-level lapse rates, some low-topped convection is forecast today. Vertical wind shear is strong, howeverm effective sshear may be to weak to support supercells. Expect some multicells that form over the mountains. These are forecast to produce some hail and severe wind gusts.