Extended Forecast
Valid: Tue 28 Jun 2022 06:00 to Wed 29 Jun 2022 06:00 UTC
Issued: Sun 26 Jun 2022 22:03
Forecaster: TUSCHY

A level 2 was issued across the Ligurian Sea into parts of N Italy and S Austria/W Slovenia mainly for large to very large hail, severe wind gusts and excessive rain.

A level 1 surrounds the level 2 with similar hazards but a lowered coverage of severe.

A level 1 was issued for parts of Norway into Sweden mainly for heavy rain and isolated hail/severe wind gusts.

SYNOPSIS

Dominant Scandinavian blocking pattern with a 3+ sigma standardized geopotential height anomaly (79-09 climate, CFSR climatology) centered near the North Cape persists during the period with ridging extending all the way down to Italy. This ridge gets framed by a long-lived strong cyclonic vortex just W of Ireland and a quasi-stationary cut-off over Turkey. The western trough crashes into this stout ridge with rapid weakening forecast over E Europe. Still, a pronounced short wave is able to cross the Gulf of Lion before opening up into a disorganized wave, which affects N-Italy during the rest of the forecast.

Regarding synoptic-scale fronts, the main feature is the slowly eastbound crawling front in the form of a cold front from S Norway to Poland and turning more into a leisurely lifting warm front over CNTRL Europe.

Regarding NWP stability there is not much to complain about. The wave over the W/CNTRL Meditherranean is rather stable regarding speed/placement and curvature with only a marginal slow down seen in last 2 GFS runs, bringing the wave more towards ICON and IFS. IFS-ENS indicate some weak member clustering of a broad/diffuse LL depression (1015 hpa range), which crosses Corse around noon and approaches the N Adriatic Sea during the overnight hours (with an increasing meridional spread of members, gradually loosing track of any LL circulation). This trend has to be monitored regarding the southward extend of potential CI all the way into CNTRL Italy with additional LL forcing.

DISCUSSION

... Parts of N/CNTRL Italy into Slovenia/S Austria ...

With the approaching wave from the SW, lowering MSLP is forecast over NW Italy into the Ligurian Sea with E-erly LL flow pushing a moist BL towards the N Apennines and the Maritime Alps. Slight discrepancies exist with the placement of the LL thermal ridge and attendant EML which results in variable W-ward expansion of the most robust CAPE plume. Up to 2000 J/kg MLCAPE evolves along the N fringe of the Apennines with similar values towards the Adriatic Sea.

Regarding CI, ample orographic and synoptic-scale lift is forecast with a prolonged period of 20-25 m/s S-erly 700 hPa flow (less at 850 hPa). Hence, scattered to widespread CI is forecast from the start of the forecast with ample MUCAPE for elevated convection with the main risk being isolated large hail and heavy rain. This risk expands towards NE Italy until noon.
This activity may enter an increasingly uncapped airmass, when crossing Austria (800-1500 J/kg MLCAPE) with DLS increasing to 10-15 m/s, so strong to severe convection is possible over CNTRL/E Austria during the afternoon hours with this activity (hail and strong to severe wind gusts). For now a level 1 covers this hazard.

Beyond noon a rapid increase of the severe risk is anticipated over the Ligurian Sea (inlcuding Corse), where all models indicate impressive MUCAPE values in the 2-3 kJ/kg range and effective DLS in the 10-20 m/s range. Organized convection with large to very large hail and excessive rain will be the main hazard with an increasing severe/damaging wind gust risk as cap erodes from the W. We could see a progressive MCS event crossing the Ligurian Sea E towards the Italian coast during the afternoon/evening hours. Capping is an issue, but confidence in adequate forcing (e.g. surface low) increased during the past few runs of various models, so upgraded to a level 2.

Another focus for organized convection arises E/NE of the N Apennines into NE Italy during the afternoon hours onwards. Loaded gun forecast soundings with LL lapse rates around 8K/km, DCAPE aoa 1kJ/kg and 20 m/s DLS indicate a risk of severe wind gusts and (very) large hail with any discrete cell. This activity may also enter S Austria and far W Slovenia.
In addition, the potential MCS event from the Ligurian Sea may cross the Apennines with an increase in thunderstorm coverage for NE Italy (scattered to widespread), although it remains unlcear how intact the MCS will be. Moreover convection switches more into the training mode over far NE Italy into S Austria during the night with convection aligning better into the S-erly background flow. Excessive rain becomes another serious concern during the overnight hours.

Finally, heavy, orographically forced rain is forecast between the Apennine Ligure and the Maritime Alps but due to ongoing uncertainties how unstable the air mass will be that far W, no level 2 was yet added.

... Poland ...

Slow moving convection along the trailing cold front may spark numerous thunderstorms with heavy rain and isolated hail the main risk. No level was yet added for now with uncertainties, where to place the cold front during peak heating (also probably modulated by convection from SWODY 1).

... S Norway and E/SE Sweden ...

Along/ahead of the gradually NE ward progressing cold front, unseasonable rich BL moisture with more than 11 g/kg LL mixing ratios pushes MLCAPE in the 500-1000 J/kg range with 15 m/s DLS (similar values for the lowest 3 km with rather strong low to mid-level frontogenesis signals). Scattered CI is forecast with a messy mode of pulsating convection and organized multicells. Hail and strong to isolated severe wind gusts next to heavy rain will be the main hazard. Of concern is the strong unidirectional flow regime, which may support temporal training of convection with growing flash flood concerns, given the high moisture content in the lower to mid troposphere and the rather deep warm cloud depth layer up to 3km AGL. Given the high impact with this risk, a robust level 1 was already added.

Another area of concern will be SE Sweden, where some models like ICON indicate still adequate BL moisture beneath the upper low for 300-600 MUCAPE build up with rapidly decreasing shear. Slow moving convection may pose a heavy rainfall threat but unclear CAPE build-up with large NWP spread precludes an upgrade for now.

... W Russia into Belarus ...

IFS indicates scattered nocturnal thunderstorm activity along a stalling cold front, but coverage of CI remains too uncertain for an upgrade for now. With up to 1000 J/kg MUCAPE, large hail would be the main issue next to a few heavy rainfall reports.

... SE Europe...

Slow moving convection beneath the upper low may pose a heavy rainfall risk with locally copious amounts of small hail but the limited CAPE input precludes a level 1 for now.

... Dinaric Alps into Greece ...

A level 1 upgrade may be needed for the mountains with highly variable CAPE/shear fields (5-20 m/s DLS and 500-200 J/kg CAPE). Isolated CI is possible with hail and downburst wind gust issues. A concentrated area for CI is not yet seen in model data, so no level 1 upgrade for now.