Extended Forecast
Valid: Sun 05 Jun 2022 06:00 to Mon 06 Jun 2022 06:00 UTC
Issued: Fri 03 Jun 2022 14:25
Forecaster: TUSCHY

Two level 2 areas were issued for severe/damaging wind gust and large to very large hail.

A level 1 surrounds both level 2 areas for similar hazards but with less coverage. An isolated tornado event is possible next to heavy rain.

A level 1 was issued for W Turkey mainly for heavy rain.

SYNOPSIS

Ongoing blocking ridge over the CNTRL Mditerranean weakens during the day with its augmented positive height anomalies pushing S towards N-Africa. Along its northern periphery, a mobile ridge moves E over CNTRL Europe with its axis crossing Poland during the night.
A mid/upper cyclonic vortex jut W of the English Channel opens up while moving E with a resulting more zonally aligned flow regime affecting the NE Atlantic towards NW France.

A quasi-stationary upper trough continues to affect SE Europe and in fact another trough approaching from the NW seems to reinforce the main/primary upper trough.

At the surface, a frontal boundary runs from N France/Benelux towards Hungary and further E towards Romania. A diffuse/elongated LL depression evolves over Benelux and modulates this boundary into a gradually lifting warm front over SE Germany into Hungary and a structuring cold front over France.

Looking into the past 5 runs of GFS/IFS and ICON, one can find the following discrepancies/uncertainties:
All 3 models have difficulties with a compact upper low over the Ukraine regarding its strength and placement, which in turn causes some zonal shifts of the ridge axis over CNTRL Europe.
IFS and GFS both indicate a strong short wave to affect the W fringe of the ridge (Switzerland/NW Italy) with good run-to-run consistency (placement and intensity). Especially IFS still indicates a bimodal solution where to track the main energy of this wave - N or S of the Alps. ICON remains an outsider with a weaker and delayed wave entering the scene from the SW. Otherwise the general height field seems to be stable in all models/runs.
To summarize, confidence in the pattern evolution is good despite aforementioned uncertainties. Convection and latent heat release of SWODY1 also dictate further NWP changes. For now we weight the SWODY2 with GFS/IFS due to some BL moisture/mid-level energy discrepancies in ICON.

Regarding the structuring LL depression over Benelux into NW Germany, IFS-ENS still has a broad swath of member spread with only few members showing some strengthening. Deterministic runs of GFS/GEM/UKMO and ICON all show stronger solutions down to 1010-1006 hPa. Not yet sure about this intensification rate as convectively induced latent heat release in NWP clusters may interact with this synoptically driven/evolving surface low which could induce focused areas of rising motion with more substantial MSLP decrease. This dveleopment has to be monitored in further runs as otherwise good upper divergence still supports a general intensification trend of this depression.


DISCUSSION

... S Germany ...

General pattern is well known for severe convection along the N Alpine rim. 500/700 hPa heights decrease constantly and noticeably over the Alps as the compact low-amplitude wave approaches from France/Switzerland.

All models show easterly BL winds over SE Bavaria into the structuring surface pressure channel (which arches into the evolving LL depression over NW Germany) and a structuring pressure wave with strong isallobaric gradients moving E/NE from Switzerland towards SE Germany.
GFS/IFS agree in 1-2 kJ/kg MLCAPE with ICON pushing into the 3 kJ/kg regime due to deep/rich BL moisture. Anyhow, CAPE is enough for DMC activity and forecast soundings show steep lapse rates at mid/low-levels.
DLS is adequate with roughly 15-20 m/s and initiating cells with evolving deviation due to intensifying dynamic pressure pertubations could rotate E along the N-Alps. Otherwise, rapidly upscale growth into an MCS with bowing segments is possible with swaths of severe/damaging wind gusts and large hail. Pattern recognition and good model agreement that far out supported an early level 2 issuance, which probably needs more adjustements/refinements later on.

... N Italy into Slovenia ...

Overall synoptic pattern supports another area with a severe MCS event. Uncertainties increase a bit keeping ICON's weaker wave solution in our mind and due to questions regarding cloud coverage (strong dust advection from N Africa could result in a dense cirrus canopy). However even with the cirrus clouds, diurnal (daytime) decrease of this event should spport some diabatic heating besides strong WAA so capping issues could decrease. Initiating convection over SW Switzerland enters a very unstable air mass over N Italy (2-3 kJ/kg) with 20 m/s 3km and 6km shear, steep mid-level lapse rates and with dry air at mid-levels. A long-lasting damaging MCS event would be the result with large hail another risk. The question remains how far S convection builds into the capped air mass, so we probably need further adjustements to the S regarding the level areas.

We neglected the ICON solution for now, which would keep cap stronger/forcing weaker and CI stapled along the mountains. We weighted more the IFS/GFS scenario (with other models trending into this direction).

... Balkan States ...

Forcing/model uncertainties increase. CAPE/shear space over Romania supports organized updrafts with a hail/wind threat but discrepancies regarding the upper low (mentioned in the SYNOPSIS) preclude any fine tuning for now.
Same for Serbia/Hungary, where better mixed LL and LCLs aoa 1.5km AGL could support long-lived clusters on a smaller scale. CI of those clusters is uncertain and also depends on convective activity from SWODY1. A partial upgrade to a level 1 seems plausible later-on (e.g. Romania).

...Belgium/the Netherlands ...

In case of the advertized LL depression, slow moving convection with heavy rain could become an issue including a few funnel/tornado reports with a potential level 1 upgrade. Aforementioned uncertainties preclude an upgrade for now.

... W-Turkey...

Another round of slow moving convection with heavy rain is forecast and caused this level 1.