Storm Forecast
Valid: Fri 02 Aug 2024 06:00 to Sat 03 Aug 2024 06:00 UTC
Issued: Thu 01 Aug 2024 23:33
Forecaster: PUCIK/ENGERT
A level 1 was issued across NE Spain mainly for large hail and severe wind gusts.
A level 1 was issued across E France, Switzerland, S Germany and Austria for large hail, heavy rainfall and to the lesser degree for severe wind gusts.
A level 2 was issued across N Italy to Slovenia and N Croatia mainly for large to very large hail, severe wind gusts and heavy rainfall.
A level 1 was issued across Croatia, Bosnia and W Serbia mainly for large hail, severe wind gusts and heavy rainfall.
A level 1 was issued across Czechia to Poland and Slovakia mainly for marginally severe wind gusts.
A level 1 was issued across Finland, NE Estonia and Russia mainly for heavy rainfall.
DISCUSSION
... Spain ...
A sharp short-wave is forecast to cross the country during the day. A strong dryline is forecast to set up over SE Spain with high CAPE values E of it and also strong capping and rather dry mid-troposphere. Initiation is very uncertain here, but any storm that could form, would have a brief time to become very severe along the dryline, before moving into very strongly capped airmass near the coastlines.
Further N, shear and CAPE will be less, but still sufficient for at least an isolated large hail or severe wind gust event from multicells or transient supercells. The initiation is more likely here with a proximity of the cold front. A level 1 is warranted for this area.
... Massif Central through Switzerland into S Germany and Austria ...
Scattered storms will form along the ill defined cold front and over the local orography. CAPE-shear overlap will allow for isolated severe storms of mostly multicell to transient supercell origin. Short-lived supercells are most likely over France and Switzerland, where the shear will be the strongest. Risk of large hail will decrease from France towards E Germany with decreasing CAPE above -10 deg C and decreasing shear. However, the risk of heavy rainfall will increase towards the east with slower storm motions and moister profiles.
... N Italy to Slovenia and Croatia ...
Models unanimously agree on the presence of MLCAPE values > 2000 J/kg over the area owing to the high low-level moisture content. Fat CAPE profiles are simulated, increasing the risk of large hail. Ahead of a weakly defined short-wave trough at the upper troposphere, moderate flow will yield 0-6 km bulk shear to reach 15 - 20 m/s, with enhanced chance of supercells. In fact, high resolution models show a number of updraft helicity swaths starting over the Alps or the Apennines with S-SE-ly orientation. In supercells, very large hail may occur as well, in combination with isolated severe wind gust threat and local heavy rainfall.
There is some uncertainty concerning the precise timing of the storms, which may be present already in the morning to early afternoon. These storms may reduce the severe weather risk for the main round of storms that should come in the late afternoon to overnight hours. The main round will occur in conjunction with the passage of the trough and the wrap-around of the cold front along the E-flank of the Alps. The activity may last till the early morning hours over some areas, particularly in the belt from the Adriatic Sea through Croatia and Bosnia into Serbia. It's possible that the storms will grow upscale in the evening or overnight, enhancing the wind gust or heavy rainfall risk.
... Czechia, S Poland, Slovakia ...
A marginal Lvl 1 is issued for the risk of isolated severe wind gusts as storms move fast along the cold front that rapidly translates E during the afternoon to evening hours. Development of linear segments will be aided by moderate 0-3 km bulk shear, reaching up to 15 m/s. Skinny CAPE and rather low LCLs will reduce the gust risk and while widespread storms may occur, most storms will produce sub-severe gusts.
... Finland through Estonia into Russia ...
Widespread storms are expected over the area posing a threat of excessive rainfall. Due to low values of deep layer shear and the mean wind the storms are expected to be slow-moving to completely stationary. The main limiting factor will be rather modest low-level moisture content, that will reduce the instantanteous rain rates.
