Storm Forecast
Valid: Tue 29 Aug 2023 06:00 to Wed 30 Aug 2023 06:00 UTC
Issued: Mon 28 Aug 2023 21:18
Forecaster: PUCIK/KUZMENKO
A level 2 was issued for S Lithuania, NE Poland, NW Belarus mainly for large to very large hail, damaging wind gusts and to the lesser degree for heavy rainfall and tornadoes.
A level 2 was issued across Hungary, Slovakia, S to Central Poland mainly for large to very large hail, severe wind gusts and heavy rainfall.
A level 1 was issued across N Lithuania, Latvia mainly for large hail and heavy rainfall and to the lesser degree for severe wind gusts.
A level 1 was issued across Romania, Bulgaria, Northern Macedonia, N Greece mainly for large hail, severe wind gusts and heavy rainfall.
A level 1 was issued across Italy, Slovenia and the Adriatic coastline mainly for heavy rainfall.
SYNOPSIS
A mid-tropospheric trough, previously associated with a deep low over the Northern Sea, will continue detachment as its base rotates from Corsica through Italy towards Serbia. Another short-wave will move from France towards Sardegna. Towards east, a pronounced ridge has built across the Black Sea and will cover large parts of Russia and also the Baltic countries. Strong mid-tropospheric flow is forecast at the base of the trough and on the flanks of the ridge. Towards the surface, a wavy cold front will remain over Poland, Slovakia and Hungary. A warm front will move quickly N from Poland through the Baltic countries with 850 hPa temperature above 20 deg C in its wake. The highest CAPE values are forecast along the warm front, where the best overlap of low-level moisture and steep mid-tropospheric lapse rates is forecast.
DISCUSSION
... Warm front region: N Poland to Belarus and the Baltics...
Scattered to widespread storms are expected to have formed along the warm front by Tuesday 06 UTC. With substantial MUCAPE and effective shear around 15 m/s, the storms may pose risks of heavy rainfall and large hail. The storms will spread further N during the day and in the overnight hours, potentially reaching S Finland by Wednesday morning. Large hail threat will persist as steep mid-tropospheric lapse rates yield substantial values of CAPE below -10 deg C isotherm.
Forecast hodographs show strong curvature, 0-500m SRH locally exceeding 100 m2/s2 and 0-1 km bulk shear well above 10 m/s along and N of the warm front. However, almost all storms will remain elevated, eliminating the tornado risk and also reducing severe wind gust risk to some degree. There will be a window of opportunity for surface-based supercells to develop in the afternoon hours over NE Poland/ NW Belarus, which would strongly increase both the tornado and severe wind gust risk.
... Cold front region: Hungary, Slovakia, S/Central Poland ...
Numerous rounds of thunderstorms are forecast across the area. The exact course of the situation will likely depend on the overnight evolution. The highest severe weather risk is forecast across Poland, where the highest CAPE is simulated. A boundary will set up across the country with well-mixed air and Inverted-V profiles to the E and very moist airmass to the W. Current thinking is that isolated supercells form first over the Carpathians with large to very large hail, followed by upscale growth into a bow-echo with threat of isolated extremely severe wind gusts as 0-3 km shear reaches 20 m/s, combined with CAPE above 2000 J/kg.
Further S, less CAPE is forecast. However, long and straight hodographs with both 0-6 km and 0-3 km bulk shear exceeding 15 m/s will still result in well-organised storms, including linear segments, bow-echoes and/or supercells. Large hail and severe wind gusts will be likely with stronger updrafts. Heavy rainfall may occur in the places, where storms move repetitively over one area. This will be of concern on the western fringes of the denoted areas.
... Romania, Bulgaria ...
Less shear is forecast compared to the N, yielding lower storm organisation, especially at first. The highest risk of severe weather is forecast in the late evening to overnight hours across the S Carpathians, where upslope flow will yield repetitive storm initiation, enhancing heavy rainfall risk. Otherwise expect isolated risks of large hail and severe wind gusts.
... Italy, Adriatic Sea coastline ...
Scattered to widespread storms will form as the short-wave trough provides environment very conducive for initiation. The storms will primarily pose risks of heavy rainfall, given the moist profiles and majority of CAPE in the warmer part of the troposphere.
