Storm Forecast
Valid: Sun 09 May 2021 07:00 to Mon 10 May 2021 06:00 UTC
Issued: Sun 09 May 2021 06:51
Forecaster: PUCIK
A level 2 was issued across eastern Spain and southwestern France mainly for damaging wind gusts, large hail, excessive rainfall and tornadoes.
A level 1 was issued across Spain mainly for damaging wind gusts and large hail.
A level 1 was issued across central / northern France and parts of BENELUX mainly for large hail and to the lesser degree for severe wind gusts.
A level 1 was issued across Denmark mainly for large hail and to the lesser degree of heavy rainfall.
SYNOPSIS
An extensive ridge stretches from the central Mediterranean into central Europe and southern Scandinavia, contributing to a highly amplified flow pattern. Deep troughs surround the ridge, one over the Atlantic and another one over the Black Sea. The Atlantic trough will slowly progress eastwards, with a short-wave attached to its base moving fast towards southern Portugal and Spain. A wavy frontal boundary is observed along the forward flank of the trough as very warm airmass has been advected from the southern Mediterranean towards northern Germany. The Black Sea trough will also progress eastwards, affecting eastern Turkey and the Caucasus region along with a cold front.
DISCUSSION
... Eastern Spain to Southwestern France ...
Modest low-level moisture along with mid-tropospheric lapse rates between 6.5 and 7 K/km will allow for a buildup of 500 - 1500 J/kg of MLCAPE over the area. Strong synoptic-scale forcing will overspread the area as the trough progresses eastwards, reducing the CIN and increasing the mid-tropospheric RH. Scattered to widespread initiation is forecast along the frontal boundary and local orography. Storm coverage will decrease from north to south of the area.
Hodographs reveal strongly sheared troposphere with 25 m/s of 0-6 km shear and up to 20 m/s of 0-3 km shear, allowing for well-organised linear segments and supercells. Isolated supercells are more likely over eastern Spain, whereas storms will likely quickly congeal into an MCS over southwestern France due to the strong linear lift along the front. Considerable fraction of storms initiating over southwestern France will also be of an elevated nature. Primary hazards will be large hail and damaging wind gusts. Large hail risk will be limited to some degree by rather skinny CAPE profiles, while damaging wind gust risk may be reduced in elevated storms. Excessive rainfall is forecast along the southern rim of the Pyrennees with numerous rounds of storms possible. With low LCLs and 0-1 km bulk shear above 10 m/s, there will be a tornado risk with isolated supercell activity. The most favorable hodographs for tornadogenesis are simulated over parts of southwestern France where 0-1 km SRH may locally exceed 200 m2/s2. The highest risk of severe weather will be present between 15 and 21 UTC period over both Spain and France, quickly diminishing afterwards.
... Central France to Denmark ...
NWP is in disagreement regarding the occurrence of an uncapped warm sector ahead of the wavy frontal boundary. Forecast Skew-Ts clearly reveal substantial MUCAPE in the wake of the front with moist profiles, suggesting elevated chances of convective initiation. Convective coverage is uncertain over the discussed area due to the lack of synoptic-scale support at the mid to upper troposphere.
In the belt from central France to Denmark, the highest likelihood of surface-based storms will be over central France, decreasing towards north. Here, severe weather threat will be the highest and isolated supercells may produce large hail and severe wind gusts.
Forecast hodographs show substantial shear above the inflow layer also for the elevated storms in the wake of the frontal boundary, so that elevated supercells / well-organised mutlicells will be possible also over parts of Denmark. Large hail and isolated heavy rain event may occur with stronger storms.
... Eastern Turkey to Caucasus ...
Widespread storms are forecast to initiate ahead of the sharp trough and advancing cold front that will quickly cross the highlighted area. Substantial deep-layer shear will promote high level of storm organisation and elevate the risk of severe weather. The most likely severe weather risk will be severe wind gusts, followed by excessive rainfall and large hail.
