Storm Forecast
Valid: Sat 14 Sep 2024 06:00 to Sun 15 Sep 2024 06:00 UTC
Issued: Fri 13 Sep 2024 21:54
Forecaster: PUCIK
A level 2 was issued across NE Czechia, NW Slovakia and S-central Poland mainly for heavy convective rainfall.
A level 1 was issued across NW Austria, E Czechia and Slovakia mainly for heavy convective rainfall.
A level 2 was issued across Moldova, Ukraine and E Poland mainly for heavy rainfall and tornadoes.
A level 1 was issued across Romania and NE Poland mainly for heavy rainfall and to the lesser degree for tornadoes.
DISCUSSION
Deep low pressure system continues to affect much of central Europe with very heavy rainfall and also severe wind gusts.
***NOTE*** This forecast only covers the contribution of CONVECTION to severe weather. Non-convective rainfall and non-convective wind gusts are NOT covered. Please refer to the warnings of the national weather institutes for more information on these hazards.
... Central-S Poland, Czechia, Austria, W Slovakia ...
Persistent warm-air advection regime is forecast across the area, yielding intense upward motion and generation of large stratiform rain shield. Forecast profiles reveal presence of a layer of elevated CAPE. CAPE is generated by the advection of moist airmass from northeast, combined with intense upward motion. While CAPE values will remain low, decreasing from Poland towards Austria, very moist profiles will allow for efficient heavy rainfall processes. Numerous bands of convective precipitation are forecast to form during the forecast period with greatly enhanced rainfall rates compared to the original stratiform rainshield. Locally, 30+ mm/h may fall, especially towards the Lvl 2 area, where higher low-level moisture content and CAPE is forecast. Rainfall intensity and the areal coverage of convective rainfall may increase towards the night, when the horizontal moisture flux will increase with low-level jet increasing to beyond 25 m/s across the whole area. Heavy convective rainfall can greatly exacerbate dangerous flooding situation, especially in the areas that already experienced heavy stratiform precipitation in the previous day.
... Moldova, E Romania, W Ukraine, E Poland ...
Scattered to widespread storms are forecast to form along and ahead of a cold front, in the zone of a synoptic-scale lift in the exit region of cyclonically curved jet at mid to upper troposphere. As the low over central Europe deepens, intensification of the low-level wind field is forecast. Ahead of the front, low-level jet is forecast reaching speeds up to 25 m/s at 850 hPa. Strongly curved hodographs are forecast basically across the whole region with 0-1 km bulk shear between 10 and 20 m/s and 0-500 SRH between 100 and 250 m2/s2. Substantial streamwise vorticity is expected in the inflow to the right-moving storms close to the ground, rendering high potential of tornadogenesis should surface-based supercells develop. Main limitation to the threat will be the low-level temperature stratification. ECMWF is more sceptical concerning surface-based storms compared to the ICON. Substantial cloudiness over the area from the early morning hours will likely preclude surface heating and steepening of low-level lapse rates. Another limitation is rather weak shear above 1 km, limiting the longevity of any supercell that forms.
Heavy rainfall will dominate the severe weather hazards and is the primary reason for Lvl 2. Skinny CAPE profiles with most CAPE in the warm part of the cloud and low LCLs will yield efficient heavy rainfall processes. With mean wind parallel to the initiating boundary, cell training can be expected.
Severe convective wind gusts will be limited by the moist lower troposphere and poor low-level lapse rates. However, given the strength of the low-level shear, isolated reports of severe gusts can not be ruled out. Large hail threat will be limited by the weak shear above 1 km and low CAPE in the cold part of the cloud. A possibility will exist over Moldova, where stronger deep layer shear and higher CAPE is forecast.
