Storm Forecast
Valid: Thu 02 Jul 2020 06:00 to Fri 03 Jul 2020 06:00 UTC
Issued: Wed 01 Jul 2020 19:54
Forecaster: PUCIK

A level 2 was issued across Belarus mainly for (very) large hail, severe wind gusts and heavy rainfall.

A level 1 was issued across the Alpine range, northern Italy, southern Germany, Slovenia and Austria mainly for (very) large hail, heavy rainfall and severe wind gusts.

A level 1 was issued for Hungary, Czech Republic, Slovakia, Poland, northern Serbia and western Romania mainly for heavy rainfall, large hail and severe wind gusts.

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

A level 1 was issued across Latvia, Estonia and northern Russia mainly for severe wind gusts and tornadoes.

SYNOPSIS

Ahead of an advancing short-wave trough that will move from the Atlantic towards western Europe, a wide belt of southwesterly flow, reaching 15+ m/s at 500 hPa is simulated will cover much of western, central and northeastern Europe. Several subtle short-waves will travel embedded in the southwesterly flow and will affect BENELUX and the Baltic states / Scandinavia. Closer to the surface, a frontal boundary will stretch from France through Germany, western Czech Republic, Poland into the Baltics and southern Finland. In the warm sector, abundant lower tropospheric moisture will contribute to widespread CAPE area reaching from northestern Spain towards southern Finland. Along and ahead of the front, scattered to widespread storms are forecast.

DISCUSSION

... Northern Italy to Russia ...

An extensive level 1 was issued in the regime supportive of isolated severe convection. In general, the environment will be characterised by low CAPE - high shear environment over the northern edge of the Lvl 1, with CAPE increasing and shear decreasing towards south. This will also be reflected in anticipated severe weather threats: northern edge of the Lvl 1 is issued predominantly for severe wind gusts or tornadoes, while the southern / southeastern part of the Lvl 1 is issued mostly for large hail and excessive rainfall. Over the Baltics and western Russia, storms will be organised in low-topped supercells or short line segments with 0-6 km shear exceeding 20 m/s. Mostly multicellular convection is forecast across the Alpine range, Czech Republic, Hungary, Slovakia and Poland with 0-6 km bulk shear between 10 and 15 m/s.

Corridors of enhanced likelihood of severe weather are forecast across:

1. Piemonte / Po valley, where CAPE values locally exceeding 2000 J/kg are forecast, along with around 15 m/s of 0-6 km shear. However, NWP models do not simulate initiation until the night, as the short-wave trough approaches the region and CAPE values decrease due to the boundary layer cooling. At that time, storms are forecast to spread over the lowlands. Well organised multi to supercells are forecast with threats of large to very large hail, severe wind gusts and also excessive rainfall. Nevertheless, uncertainty regarding the convective coverage in the late afternoon to evening hours precluded issuance of Lvl 2 atm.

2. Estonia / Latvia to western Russia

While only marginal CAPE values are simulated by the model, pronounced synoptic-scale lift will aid in the initiation of scattered to widespread storms. With 0-3 km shear exceeding 15 m/s, line segments will be capable of isolated severe wind gusts. While hodographs will mostly stay linear, 0-1 km shear around 10 m/s combined with pronounced low-level CAPE will enhance the tornado threat with low-topped supercells.

3. Belarus

Here, MLCAPE values in between of 1500 to 2000 J/kg will combine with 0-6 km bulk shear values of 15 - 20 m/s, promoting strong and well-organised storms. Convective mode will be dictated by mesoscale details regarding the lift, but the large-scale environment will be supportive of both (very) large hail and severe wind gusts.

... Northeastern Spain ...

NWP simulates convective precipitation breaking out over the mountainous areas in the afternoon hours, but it is possible that storms will progress towards lowlands (Ebro valley) as synoptic-scale lift overspreads the area during the night. 0-6 km bulk shear values approaching 25 m/s point to the high likelihood of supercells given succesfull initiation with threats of isolated large hail and severe wind gusts.