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Storm Forecast
Valid: Fri 21 Jun 2024 06:00 to Sat 22 Jun 2024 06:00 UTC
Issued: Thu 20 Jun 2024 21:40
Forecaster: TUSCHY
A level 3 was issued across parts of Czechia into E-Germany, SW Poland and far NE Austria mainly for damaging wind gusts and/or very large to giant hail.
Another level 3 was issued for parts of N-CNTRL Italy for similar hazards like the first level 3. A strong tornado event is possible.
A level 2 surrounds both level 3 for similar hazards but with lower probabilities. Heavy to isolated excessive rain is forecast next to a regionally augmented tornado risk.
A level 1 surrounds both level areas with lower probabilities of all kind of hazards including a few tornadoes over parts of France.
A level 1 was issued for parts of SW Russia mainly for heavy rain and hail.
SYNOPSIS
Some marginal shifts in the wave crests occur over CNTRL Europe as the trough over NW Europe shifts a bit more E into the central parts of Europe. Meanwhile, the dominant subtropical ridge with an attendant plume of hot and rather dry arid air weakens a bit over SE Europe with a northward reaching ridge covering most of E-Poland into Slovakia during the evening hours.
Elsewehere a stationary cut-off over the far E Mediterranean creates an high-over low blocking pattern, which persists during this forecast. More progressive troughs enter/affect W Russia and advect a rather cool and stable airmass far S.
Along the surface, a wavy meridionally aligned boundary stretches from Germany into the CNTRL Mediterranean, which is expected to move east during the forecast. This front is embedded within a rather broad trough of lower MSLP with ECMWF ENS indicating numerous clustered member maxima for weak/transient LL vortices. Latest EZ run has one over far NW into N-CNTRL Germany, another one evolving over CNTRL Poland and a potential third one E of the Alps into Hungary. Ongoing broad member spread and weak intensity signals keep confidence rather low regarding development. Placement of mid/upper-level jets however supports a somewhat more focused pressure decrease from N Germany into CNTRL Poland: either a more dominant vortex or numerous weaker ones.
One word added to the dust issues. Latest forecasts indicate a rather modest dust load into our area of interest, which covers most of CNTRL into E-CNTRL Europe. There will be some issues once again as dust advects into a broad WCB, but modest dust load and less focused H700-300 hPa moisture advection probably supports a gradual break up of any dust loaded clouds during the daytime hours.
This issue combined with a very unstable/dynamic setup cause any model errors to grow more rapidly betimes with still substantial model spread present.
EFI CAPE/shear is significantly enhanced over CNTRL into E-CNTRL Europe with SOT 2+ and same for IVT with positive SOT values.
... Switzerland to Germany into Austria, Czechia and Poland ...
The frontal zone from Germany into Switzerland will be the main focus for ongoing/early CI. A messy mode of more stratiform rain mixed with convective segments is forecast within the WCB regime with weak/modest MUCAPE. Most models agree in a rapidly NE ward racing low-amplitude wave, which exits Switzerland into S Germany during the morning hours onwards. This activity is probably non-severe and creates a dent in the CAPE field with missing heating and rain-cooled air spreading from SW Germany into the central parts of Germany.
E-Switzerland may see an augmented risk for ongoing supercell/bow echo activity from the previous night with large hail and damaging wind gusts. This risk exits E until the early afternoon hours. During the afternoon, more strong to isolated evere storms move in from the W with an hail/strong gust/heavy rain and isolated tornado risk as LCLs remain low with good antistreamwise vorticity for left moving storms.
For W into CNTRL Austria, multiple rounds of organized/severe convection occur with all kind of hazards, including excessive rain, very large hail and damaging gusts.
From W to N Germany, a passing/structuring LL vortex creates a band of enhanced LL frontognesis which becomes the focus for scattered thunderstorm development. Temporal diabatic heating should push MUCAPE in the 400-1000 J/kg range with decent DLS in excess of 20 m/s for strong to severe thunderstorms. PWATs around 30 mm and elongated CAPE profiles with highest conentration above -10C (plus high 0C level) indicate heavy rain and lots of small hail/isolated large hail the main issue. Although LL shear is modest, we do not rule out a few tornado events with low LCLs and some better LL helical inflow for deviating cells. In fact, if we get some better clearing, we cannot rule out a few longer-lived supercells with all kind of hazards especially over NW Germany.
In case we see a structuring LL depression over N Germany, a regionally enhanced heavy rainfall risk with clustering/slow moving convection could arise over NW into N-Germany.
The severe risk over NE Germany probably increases during the day ahead of the short-wave driven area with thundery rain, which approaches from the SW and starts to weaken until noon. This precipitation is driven by the NE-ward travelling short wave/IPV maximum so we could see CI along the periphery of the stratiform rain somewhere from CNTRL into N-CNTRL Germany.
Conditions over E/NE Germany are supportive for long-lived supercells which turn more E betimes as MUCAPE increases from Berlin to the Ore Mountain from 800 to 2000 J/kg with 20-25 m/s DLS. These storms move into a high-energetic and very moist airmass with hight PWAT anomalies, so there is a growing concern for a few tornado events including a strong one. In additon, large to very large hail and strong to severe wind gusts are possible as well. Of note is that despite progressive nature, this convection will be rather effective in producing extreme rainfall amounts with PWATs in excess of 40 mm.
Supercells then move into N Poland with an ongoing severe to isolated extremely severe risk (hail/wind). We would not be surprised to see a maturing/severe bow echo to race along the CAPE periphery into CNTRL Poland with swaths of damaging gusts and severe hail. Hence we expanded the level 3 that far N.
Finally, we have to discuss a broad corridor from Austria into SE Germany, Czechia and Poland, where the CAPE/shear space assists in a mixture of long-tracked supercells, bow echoes and upscale growing convection into severe MCS events.
CI for this activity probably occurs around noon onwards over W-CNTRL Austria and Czechia into SE Germany. These areas experience a CAPE/shear space favorable for rapid storm organization with CNTRL/E Austria and Czechia showing top-down weighted CAPE profiles in the 1.5-3 kJ/kg range and 20 m/s DLS or 15 m/s 0-3 km shear. Initiating cells will produce very large to giant hail next to a few damaging downburst events. Within an high PWAT environment, deeply/well mixed BL conditions and high CAPE, rapidly growing/maturing cold pools tend to cause upscale growing convection into progressive MCS events - either numerous smaller ones, or merging into a massive MCS before entering Poland.
Latest idea is that the first area of augmented concern for a derecho-like event arises from extreme E-Germany into N/CNTRL Czechia and further E into Poland, following the SW-erly mid-level flow and good 0-3 km shear. Some CAMs show RIJ dynamics in excess of 30 m/s just above the surface along this corridor.
Another region with swaths of hurricane-forced gusts may evolve from E Austria further E/NE but this depends more on the cold pool strength. However we see not much in the way for a severe MCS event affecting also far NW Hungary into Slovakia and S Poland during the evening/night with a gradual decrease in intensity betimes. Next to the wind risk, damaging to giant hail (combined wind/hail risk) and excessive rain become another issue. The tornado risk is an isolated one due to high LCLs, but mature supercells can do the trigger as can merging cells or supercells riding a mesocale boundary.
das ist aber schon etwas irre...
