Storm Forecast
Valid: Thu 17 Aug 2023 06:00 to Fri 18 Aug 2023 06:00 UTC
Issued: Wed 16 Aug 2023 21:57
Forecaster: PUCIK/KUZMENKO

A level 1 was issued for a large belt from central France to Latvia and extreme W Russia mainly for excessive rainfall and large hail.

A level 1 was issued across N Russia mainly for severe wind gusts and to the lesser extent for tornadoes.

SYNOPSIS and DISCUSSION

A weak geopotential field will dominate the synoptic-scale situation across Europe. The only exception will be a short-wave trough that will move from Finland towards N Russia during the day. Several weak lows are forecast at the upper troposphere across W/central Europe, the first one across E France/W Switzerland, another one across Poland. Closer to the surface, a frontal boundary will run from N France through N Germany into the Baltic Sea, Estonia and further into Russia.

South of the boundary, moist low-level airmass, characterized by dewpoints between 16 and 20 deg C, yields widespread MLCAPE values around 1000 J/kg. A large belt of Lvl 1 is issued for heavy convective rainfall, given slow storm motions across majority of the areas and moist low to mid-troposphere, and large hail from central France to Latvia and W Russia. The highest risk of large hail is forecast across N Italy, where the highest CAPE is forecast, and S Germany and the E Lithuania and Latvia, where mid-tropospheric lapse rates will exceed 6.5 K/km. Isolated downbursts are possible as well given abundant precipitation loading within the updrafts. In general, storms will be organised into multicell clusters given conditions easy for initiation and mediocre shear mostly below 15 m/s in the 0-6 km layer. Stronger shear is forecast across N Russia, where a well-organised squall line along a cold front may result in isolated severe wind gusts. 0-1 km shear around 10 m/s along with slight hodograph may lead to one or two tornadoes if supercells form along the front.

It is possible that coverage of rain and hail reports over one or more areas will satisfy Lvl 2 criterion. However, there is large discrepancy in the NWP models (both global and high-resolution ones) concerning exactly where and how many storms will form during the day. Due to this uncertainty, will refrain from Lvl 2. Forecasters are advised to monitor local convection initiation areas, such as orography, outflow boundaries laid out by previous storms and the frontal boundary at the N edge of the Lvl 1 area.