Storm Forecast
Valid: Wed 17 Aug 2022 06:00 to Thu 18 Aug 2022 06:00 UTC
Issued: Tue 16 Aug 2022 19:49
Forecaster: PUCIK
A level 2 was issued across the W Mediterranean into SE France, W Switzerland and N Italy mainly for large to very large hail, excessive rainfall, severe wind gusts and tornadoes.
A level 1 was issued across NW France and BENELUX mainly for excessive rainfall.
A level 2 was issued across NE Sweden and NW Finland mainly for severe wind gusts and to the lesser extent for tornadoes.
A level 1 was issued across Scandinavia mainly for severe wind gusts.
A level 1 was issued across S Russia mainly for large hail.
SYNOPSIS
A deep trough will stretch from W Atlantic through N France into Iberia. Strong flow is simulated at the forward flank of the trough, especially across the western Mediterranean with 500 hPa windspeeds up to 30 m/s. A plume of steep lapse rates is forecast to develop across W Iberia and another plume will have advected from N Africa. Considerable overlap of steep mid-tropospheric lapse rates and abundant low-level moisture is anticipated over the W Mediterranean with MLCAPE values exceeding 3000 J/kg.
Towards the north, a short-wave trough and a pronounced cold front will cross Scandinavia during the forecast period. Ahead of the cold front, mixing ratios exceeding 12 g/kg will secure a large area of MLCAPE > 500 J/kg.
Further storms are expected near the shallow low over Ukraine and the Black Sea.
DISCUSSION
... E Iberia to SE France, N Italy and W Switzerland ...
Well-organised convective storms are forecast in this region with 0-6 km bulk shear reaching 15 - 30 m/s, increasing from north to south. MLCAPE values will be the highest over the Mediterranean Sea, where surface dewpoints observations show values of 20 - 24 deg C. Plume of steep lapse rates will also stay confined to the sea. Thus, the highest probability of (extremely) severe storms given the successful storm initiation will be over the sea and the adjacent coastlines, decreasing further inland. Supercells and well-organised convective systems with a high probability of severe weather are anticipated across the whole Lvl 2 area. The storms may be capable of all severe weather hazards. The highest risk of excessive rainfall and tornadoes will exist over S France and the Gulf of Genoa, where the strongest low-level flow is simulated.
The storms will spread E during the day as the upper level low, as well as the surface cold front move in this direction. Towards the night and morning hours, abundant storm activity is forecast over N Italy. This development will likely become an important factor in the subsequent convective scenario on Thursday.
... France to BENELUX ...
Slower moving storms in weak to moderate shear are forecast in this area. The primary threat will be excessive precipitation.
... Scandinavia ...
A fast-moving cold front is forecast to cross the area with a strong low-level wind field, reaching 15 - 25 m/s near 850 hPa level. With flow parallel to the front and strong low-level forcing, widespread initiation is forecast and the most likely convective mode will be a squall line. As the system moves fast towards E, severe wind gusts are expected. Lvl 2 is issued for the area with the strongest low-level wind field and thus also the most pronounced severe wind risk. Tornadoes are also possible given 0-1 km bulk shear > 10 m/s, but with shear confined mostly to the bottom 1-3 km and strong forcing, it is not so likely that isolated supercells manage to develop.
... S Russia ...
Isolated to scattered storms will develop in the evening to night across the area. Decent CAPE above -10 deg C along with deep layer shear around 15 m/s suggests enhanced threat of large and perhaps even very hail with these storms.
