Storm Forecast
Valid: Wed 15 Jun 2022 06:00 to Thu 16 Jun 2022 06:00 UTC
Issued: Tue 14 Jun 2022 23:04
Forecaster: TUSCHY

A level 1 was issued for parts of S-CNTRL Europe mainly for large hail and severe wind gusts. Locally heavy rain is possible.

A level 1 was issued for parts of Portugal and NW Spain mainly for large hail and severe wind gusts.

SYNOPSIS

Zonal flow aloft covers most of Europe with a more prominent upper trough situated over NE Europe. Embedded in this flow regime, numerous low amplitude waves move E/SE over CNTRL into SE Europe.

SW Europe remains beneath a strong ridge with 500 height readings around the 90th percentile range, whereas 850 hPa temperatures once again hover along record readings (25-30C over CNTRL Spain, lowering to 20-22C over S France).
A gradually northward crawling cut-off just W of Portugal backs this ridge and both features remain in a steady state for this period.

A diffuse and only slowly structuring warm front runs from E-CNTRL France to the E towards the Alps.

DISCUSSION

... S France to Switzerland and Italy ...

Confidence in CI did not change substantially compared to yesterday's SWODY2.
Over SW France, rich BL moisture beneath 3-6 km lape rates around 8 K/km offers 2 to 2.5 kJ/kg MUCAPE or 1.5 kJ/kg MLCAPE. The 850 to 700 hPa layer however remains quite warm with 850 hPa readings not lower than 20 C - even increasing during the overnight hours. Hence capping should be stout including ongoing weak background subsidence so confidence in CI remains too low to include this area into a lightning/level area. In addition, even in ensemble data we see no member which indicates CI.

Hence we focus on the orography from SE France to the Alps, where diabatic heating and gentle upslope flow increase confidence in CI substantially. Colder 850-700 hPa layer with only slightly weaker 3-6 km lapse rates offer 500-2000 J/kg. The CAPE field is highly inhomogeneous and bound to the orography as mesoscale adds an important input with respect to local moisture pooling (e.g. Alpine pumping). NWP guidance varies with regional stronger mid-level flow but overall 10-15 m/s DLS seems to be a reasonable guess for this setup.
A mix of multicells/isolated transient supercells is forecast with large hail and severe downbursts the main hazard. The wind risk is enhanced with up to 8K/km 0-3 km lapse rates and DCAPE aoa 1000 J/kg, so healthy cold pools should push wind gusts into the severe criteria including the rsik for temporal line-ups with swaths of strong to severe wind gusts.
With time, thunderstorms enter N-Italy from the N and W, so colliding clusters pose an excessive rainfall threat before overall activity weakens until midnight.

The same for CNTRL Italy with large hail/severe wind gusts the main hazard. Offshore blowing gust fronts atop the Adriatic and Ligurian Sea may pose a marine hazard regarding severe wind gusts.

We broadened up the level 1 area to include the increased chance for longer lived (cold pool driven) cluster activity despite weak background (synoptic) support. Thought about adding a level 2 area, but missing focus for most concentrated (significant) severe precluded any upgrade for now.

... Portugal and Spain ...

NWP guidance still indicates a chance for CI and current (21Z) sat loop with <60C cloud tops over NE Spain fosters this expectation. Slighly warmer 850 hPa temperatures over NE Spain should limit CI to isolated, but once again orographically induced CI on a local scale is forecast with isolated hail/severe downbursts.

More focused synoptically driven lift including an approaching cold front from the SW increase probabilities into the "scattered category" over Portugal and NW Spain. Excluded impressive helical values in lowest 3km due to elevated nature of convection, but still enough shear is forecast for organized updrafts with large hail and bursts of heavy rain. NWP guidance diverges substantially regarding coverage but confidence for adequate CI remains high enough to keep a level 1 for this area.

... S Germany ...

Of interest is a slowly amplifying wave, which emerges from the English Channel during the overnight hours and moves rapdily E. Numerical guidance is rather constant with placement and strength of this feature. It remains questionable how well it interacts with the unstable plume over S-CNTRL Europe. Ensemble data gives some low-end chances for limited overnight thunderstorm activity developing over S Germany. For now only a low probability lightning area was added but would not be surprised to see numerous elevated/non-severe thunderstorms during the morning hours over S and potential E-CNTRL Germany.

... Lightning areas ...

Did not add any level 1 areas due to a separated CAPE/shear space. On the mesoscale a few strong to severe thunderstorms may occur, but that's too marginal for an upgrade.
However, Belarus will see a diurnal driven uptick in CAPE up to 400 J/kg with robust 0-3 km CAPE values (driven by up to 8.5 K/km 0-3 km lapse rates). Combined with 10-15 m/s 0-1 km and 0-3 km shear, numerous strong to isolated severe wind gusts are possible and even a transient rotating updraft with hail issues and one or two tornadoes can't be excluded (low topped supercells). IFS and ICON support this scenario with GFS indicating a weaker CAPE/shear space so with ongoing model discrepancies no upgrade was performed.

Another focus was the NE ward sliding cold front into Russia, but strongest post frontal flow remains decoupled from the instability axis along/ahead of the front.