Storm Forecast
Valid: Wed 02 Aug 2023 06:00 to Thu 03 Aug 2023 06:00 UTC
Issued: Tue 01 Aug 2023 19:58
Forecaster: GROENEMEIJER

A level 2 was issued across the Caucasus region, mainly for large hail and very heavy rainfall, and to a lesser extent for severe wind gusts.

A level 1 was issued across an area surrounding the level 1 region, for the same risks.

A level 2 was issued across a part of North Germany for tornadoes, severe wind gusts, and marginally large hail.

A level 1 was issued across an area surrounding the level 2 for tornadoes, severe wind gusts, and large hail.

A level 1 was issued across parts of Finland, Estonia, Latvia, Belarus, Ukraine, and Moldova for heavy rainfall, and across Finland for isolated tornadoes, too.

SYNOPSIS

A strong westerly jet streak south of a close low initially located over the Irish Sea is translating eastward. Within its left exit region, severe thunderstorms are expected to develop across northwest Europe. Further east, storms are expected to redevelop ahead of a slow-moving cold front stretching from Lapland to Romania. Further downstream, across the Black Sea, Turkey, and the Caucasus region, mid-level flow is rather weak, but a shortwave trough should yield some forcing for upward motion to support widespread initiation of storms.

DISCUSSION

Caucasus...

Abundant instability is expected to develop aided by solar heating. The resulting thermodynamic profile is very moist and exhibits most CAPE high in the storm. This suggests that both a risk of very heavy rainfall and of hail will exist. The risk of large hail is limited by the lack of strong deep-layer shear. Numerical Weather prediction models agree on the development of widespread convection ahead of the approaching shortwave trough from the west. Given the slow movement of storms, high rainfall amounts are expected that could lead to local flash floods. In addition, some locally high accumulations of hail may develop.

Northwest Europe...

Behind a cold front, a strong mid- and upper-level jet streak with wind speeds as high as 50 m/s at 500 and 65 m/s at 300 mb moves eastward, affecting the level 1 and 2 areas. Within the left exit quadrant of the jet streak upward motion supports the destabilization of the air mass, which should lead to the development of convective storms, across the southern Benelux around and just after local noon. The storms are expected to increase in coverage and move eastward into Germany during the afternoon.

The storms' severe potential is caused in particular by the strong wind shear in which they develop, with 0-3 km bulk shear around 20-30 m/s. Moreover, high storm-relative helicity with 100-200 m/s in the 0-1 km layer is forecast. This suggests the storms will probably develop into rapidly moving low-topped supercells with an attendant risk of tornadoes or small bow-echoes with a downburst risk. Given the strong shear, a strong tornado is not out of the question. In addition, large hail of 2-3 cm in diameter can be expected with the strongest storms. During the late evening, storm intensity should subside as the boundary layer cools.

Lapland to Moldova...

A long area of storm activity within a warm advection region is expected to reintensify during the morning and afternoon with a modest and varying risk of several convective hazards. Across Finland, significant values of storm-relative helicity and low cloud bases suggest that one or two tornadoes may develop with surface-based prefrontal storms or with storms along the front. Furthermore, training of storms may occur, leading to some heavy rainfall. Further south, across parts of Russia, Estonia, Latvia, Belarus, Ukraine, and Moldova, the risk is mostly limited to very heavy rainfall with training and slow-moving storms. Any hailfall will be mostly sub-severe except across Ukraine and Moldova where CAPE is a bit higher, and with any rotating updrafts across Finland.