Storm Forecast
Valid: Sun 26 Jun 2022 06:00 to Mon 27 Jun 2022 06:00 UTC
Issued: Sat 25 Jun 2022 15:50
Forecaster: TUSCHY
A level 2 was issued for SE/E France, W/NW Switzerland into SW Germany mainly for large to very large hail and severe wind gusts. Within the southern part of the level 2, excessive rain becomes an additional threat.
A level 1 surrounds the level 2 for similar hazards but with a lower severe coverage. An isolated tornado is possible.
A level 1 was issued for NE Germany mainly for excessive rain. Further north (Denmark to S Sweden/Norway) the risk switches to a hail/wind gust threat with heavy rain.
A level 1 was issued for NE Sweden into Finland mainly for heavy rain.
A level 1 was issued for W Russia mainly for large hail and severe wind gusts.
A level 1 was issued for parts of SE Europe mainly for large hail, heavy rain and severe wind gusts.
SYNOPSIS
A quasi-steady wave pattern over Europe features a Rossby-wave (amplified down to Marcco) with a building Scandinavian blocking pattern/anticyclone over NE Europe. In addition, rex blocking (transforming into high-over-low) occurs over E Europe with a pronounced cut-off along the S fringe of the blocking anticyclone.
The wave/ridge pattern is bisected by an undulating synoptic-scale boundary, which oscillates E/W next to weak/diffuse/broad LL depressions.
No serious mid-level energy lifting along the E fringe of the trough is forecast with the main focus for CI residing along the orography/the synoptic-scale boundary.
DISCUSSION
... SE/E France into W/CNTRL/SW Germany and W/NW Switzerland ...
The day starts with an augmented chance for training convection along the SE Massif Central, where strong LL storm-relative inflow feeds ongoing convection (from the previous night) with lots of marine moisture. Excessive rain will be the main risk although any more discrete cell experiences a favorable CAPE/shear space (1000 J/kg MUCAPE and in excess of 20 m/s DLS) for rotating updrafts with large to very large hail. A level 2 was added for this activity, which weakens until noon.
The main focus for DMC activity then resides along/ahead of the synoptic-scale boundary with prefrontal air mass offering abundant BL moisture (BL mixing ratios of 12-14 g/kg) beneath neutral mid-level lapse rates. Anafront-type character with weak mid/upper-level lift (also upshear) should assist in adequate diabatic heating within the area of interest with MUCAPE readings in the 1-1.5 kJ/kg range.
Brisk SW-erlies with gradually strengthening mid-level winds push DLS in the 20-25 m/s range with slightly weaker readings in the 0-3 km layer (10-20 m/s with an increase towards SE France with strongest 850/700 hPa frontogenesis and cross-circulation along the front). Of interest is the pronounced veering with height in tandem with strong WAA/positive thickness advection within the unstable air mass.
Current expectation is CI of preliminarily elevated convection along the E fringe of the anafrontal rain shield around noon. This activity poses a hail and rain threat.
Betimes, convection builds E/NE into the favorable CAPE/shear space with rapid DMC intensification forecasts. Betimes with intensifying internal pressure perturbations, deviating storm motions into (then) SRH-rich and unstable air should support a few long-tracked supercells with very large hail, damaging winds and an isolated tornado threat (despite iffy looking BL conditions with poor LL lapse rates). We broadened the level 2 into W/NW Switzerland due to ongoing EPS spread with respect to CI and consequent cell tracks. Same for S France, where onshore moisture advection beneath cooler mid-levels broadens CAPE field more to the W/NW.
Further downstream, SW in CNTRL Germany, isolated CI is possible within the warm sector and well ahead of the aforementioned activity. Main CI should occur along the Vosges/Black Mountains and Allgeau with a few discrete supercells moving NE/E betimes. NPW guidances tries to suppress activity rapidly E of the orography, but don't see too many reasons against one or two longer tracked supercells into W-Bavaria. Large hail and severe wind gusts will be the main risk with this activity, which weakens during the eving hours with the loss of heating. It remains unclear how far N the risk of isolated CI extends which could also cover most of CNTRL Germany (Hessen into S Lower Saxony and W Thuringia). Due to the overall limited coverage of storms a level 1 should cover this risk beside confined swaths of level-2 like hail/wind risks beneath individual supercells.
During the overnight hours, clustering and mostly elevated convection affects E Germany with confined swaths of heavy rain. Weak MUCAPE and modest effective shear could also support an isolated hail risk with stronger cells, but overall conditions won't support a level 1 for now.
... NE Germany ...
Another round of slow moving thunderstorms with a localized threat of excessive rain is forecast within a weak/broad LL low pressure channel, filled with a moist air mass (2m dewpoints in the upper tens). Roughly 1.5 kJ/kg MLCAPE with 10 m/s or less DLS favor clustering multicells with copious amounts of small hail and heavy/excessive rain. Broad EPS spread and model-to-model spread keeps any level-2 upgrade too woolly and hence a broad level 1 was added.
... Denmark, Norway, Sweden into Finland ...
Along the fringes of the blocking anticyclone, pooling BL moisture beneath neutral mid-level lapse rates assists in pockets of enhanced MUCAPE build-up within the level 1 areas. DLS decreases from 15 m/s (Denmark, S Norway/Sweden) to 5-10 m/s over NE Sweden/N Finland. Hence a hail/wind/rain threat exists with stronger shear (S Norway/Sweden and Denmark) and turns to a heavy rain risk further NE.
During the night, the severe risk vanishes betimes excluding N Finland, where enhanced nocturnal convection along a wavy frontal boundary is forecast with augmented shear in the 10-15 m/s range. Forecast soundings indicate mainly elevated convection, so heavy rain and gusty winds become the main hazard. No level areas was issued for this activity.
... SE Europe ...
Cool mid-levels atop seasonable BL moisture offer 500-1000 J/kg MUCAPE during the afternoon hours. DLS increases from Romania to Greece from 5 m/s to 20 m/s and scattered to widespread CI is forecast either along the orography or along residual outflow boundaries from previous convection (beside a supportive background support by a pssing short wave). A level 1 due to hail/wind and rain was issued with variable main foci.
... W Russia ...
A level 1 for hail/wind was added for W Russia with long hodographs and 1500 J/kg MUCAPE. Multicells/isolated supercells bring large hail and strong to severe wind gusts.
... Ireland ...
Daytime driven LLCAPE increase with values up to 400 J/kg LLCAPE augment the temporal risk of a few funnel/short-lived tornadoes, but the general risk is too marginal for a broad level 1 area.
