Storm Forecast
Valid: Wed 01 May 2024 06:00 to Thu 02 May 2024 06:00 UTC
Issued: Tue 30 Apr 2024 21:00
Forecaster: PUCIK
A level 2 was issued across France mainly for large to very large hail, severe wind gusts and to the lesser degree for heavy rainfall and tornadoes.
A level 1 was issued across Belgium mainly for large to very large hail, severe wind gusts and to the lesser degree for tornadoes.
A level 1 was issued across S Netherlands and W Germany mainly for severe wind gusts and large hail.
A level 1 was issued across extreme NW Spain (Catalonia), Italy and Croatia/Slovenia mainly for heavy rainfall.
A level 1 was issued in a belt from N Africa to Corsica and Sardegna mainly for large hail and severe wind gusts.
A level 1 was issued across Turkey and Middle-East mainly for heavy rainfall.
DISCUSSION
... E/NE France to Belgium ...
A frontal wave is forecast to develop along a cold front stretching across France. Cyclogenesis is simulated by all models, but some uncertainty remains concerning the exact placement of the wave in the front. An agreement in the models exists concerning:
1. High values of CAPE in the warm sector ahead of the front thanks to the advection of steep lapse rates from E which were generated by the downslope winds behind the Alps
2. Strengthening shear towards the evening hours. Models simulate strongly curved hodographs with moderate 0-3 and 0-6 km bulk shear reaching up to 15 m/s. Majority of the bulk shear is forecast in the bottom 1 to 3 km.
3. Strongest lift on the cool side of the boundary thanks to the pronounced warm air advection and isentropic lift with very moist profiles and elevated CAPE. Here, the coverage of storms will be the highest and initiation is much more uncertain over the warm sector.
Regardless of whether surface-based or elevated, storms will pose risks of large to very large hail given high CAPE values below -10 deg C and that some storms will become supercells. Risks of severe wind gusts and tornadoes are more conditional upon the storms developing also on the warm side of the boundary. The tornado risk will be most pronounced close to the front or just to its cool side where the storms can still be surface-based and where modest low-level shear is forecast between 18 and 21 UTC. Severe wind gusts will be likely with any storm that can develop deeper in the warm sector towards Germany, where inverted profiles are forecast. However, here, initiation is very questionable given lack of lift and rather low RH around the LFC.
Storms will likely begin to develop in the early to late afternoon hours on the border with Switzerland and spread further N/NW. Lvl 2 is introduced for the corridor, where the highest coverage of severe is forecast. Here, an upscale growth of convection is possible as the storms travel with the zone of forcing and main severe weather hazard may shift from large hail to heavy rain and severe wind gusts.
... W Italy coastline to the Alps and Croatia ...
Several rounds of showers and storms are forecast across the area. Forecast soundings and hodographs show predominantly heavy rainfall threat with rather skinny CAPE profiles, majority of CAPE in the warm cloud zone and low LCLs. The threat will be maximized over the Alps and Istria/S Slovenia, where strong upslope/onshore flow is forecast as well. Across NW Italy, over the plains, there will be a marginal risk of tornadoes given 0-1 km bulk shear above 10 m/s in case that a right-moving storm can develop.
... N Africa through the Balearic Sea to Sardegna and Corsica ...
A conditional lvl 1 is issued across this area as a trough ejects from Iberia. While a strong forcing is forecast to cross the region along with a surface cold front, models indicate either no or only very isolated initiation with exception of N Africa. Here, the CAPE will be marginal while the shear will be strong, resulting in a predominance of severe wind gusts as a main threat. Towards the sea, CAPE will get higher in the evening to overnight hours as steep lapse rates are advected from W. In case the storms manage to form, substantial CAPE below -10 deg C, combined with moderate shear should yield at least an isolated threat of large hail.
... NW Spain (Catalonia) ...
A heavy rainfall event is possible across the area owing to the strong forcing overspreading the area with the passage of the deep trough from the SW. Other hazards will be limited by low CAPE and rather modest shear.
... Turkey to Middle East ...
Widespread storms are forecast underneath weak geopotential field. Forecast soundings reveal skinny CAPE profiles, low LCLs and slow storm motions, yielding primary threat of heavy rainfall and subsequent flash flooding.
