Storm Forecast
Valid: Fri 14 Jun 2019 06:00 to Sat 15 Jun 2019 06:00 UTC
Issued: Fri 14 Jun 2019 00:15
Forecaster: TUSCHY

A level 1 was issued across parts of Germany mainly for large hail, severe wind gusts, heavy rain and regionally enhanced tornado probabilities.

A level 1 was issued across parts of SE-France and NW-Italy mainly for large hail, severe wind gusts and excessive rain.

A level 1 was issued for parts of E-/SE-Europe mainly for large to isolated very large hail, severe wind gusts and excessive rain. An isolated tornado event is possible.

A level 1 was issued for parts of Turkey mainly for excessive rain.

SYNOPSIS

Blocking pattern continues with low geopotential heights over W/NW-Europe and ridging over the CNTRL Mediterranean to the Alps. A broad upper low continues to spin over Turkey whereas a progressive NW-erly flow regime affects far NE-Europe.

A cold surge is about to stall over SE Poland to Belarus. This boundary separates cool and more stable air to its north from very unstable air to its south. In addition, falling pressure over Germany and a general backing wind field re-strengthens the boundary from E-Germany into W-Poland during the night and a structuring warm front is forecast to drift north towards E/NE Germany until 06Z.

DISCUSSION

... Far N-Germany ...

A sharp and progressive short wave crosses the German Bight during the daytime hours. This feature interacts with a plume of unstable air which evolves within a confluent low-tropospheric flow regime (with its axis running from S-Denmark to the Hamburg vicinity). MLCAPE is forecast to reside in the 400-800 J/kg range with locally higher peaks along any convergence axis. WAA regime with veering profiles affects most of far NW/N-CNTRL Germany with SRH-3 in the 200-300 m^2/s^2 range and roughly half the magnitude in the 0-1 km layer.
A bit surprising are mixed signals in the model guidance, showing either supressed or more active thunderstorm development along the convergence zone. Not much CIN in place with some diabatic heating being forecast, so there is no obvious reason why not scattered cells should evolve. The main negative factor could be bad phasing of the passing short-wave and the structuring convergence zone, with the latter maturing behind the northward lifting wave and hence in an increasingly NVA regime. Still enough lift should be available for isolated to scattered CI.
15-20 m/s DLS and strongly curved 0-4 km hodographs support rotating updrafts with large hail and severe wind gusts. Despite LCLs around 1 km AGL, we do not want to exclude a tornado event due to the favorable low-tropospheric kinematic environment. No level 2 was issued with ongoing uncertainties of thunderstorm coverage.

... CNTRL,-E-,N-Germany during the night ...

A gradually consolidating warm front lifts N with far E-Germany residing in the true (surface based) warm sector until 06Z. This warm front features a strong tilt to the W and N with an attendant MUCAPE plume extending all the way to W-CNTRL Germany. Enhanced frontogenesis along that tilted front and an approaching mid-level short wave from the SW add enough lift for a gradual increase in convection during the night over an extensive area, including most of CNTRL-, W-, N- Germany and Benelux towards the S-North Sea. In fact, influx of high low-tropospheric moisture content from the E probably supports a growing overnight cluster of elevated thunderstorms over CNTRL Germany, which lifts N during the night. Effective DLS in the 15-20 m/s range and several hundreds J/kg MUCAPE result in an isolated large hail risk next to heavy rain.

The region along the tip of the surface warm front interacting with the E-fringe of the evolveing cluster has to be monitored closely for (near) surface based thunderstorm development over N-CNTRL and NE-Germany beyond 00Z. In addition there is a chance that the cluster gradually tends to build into the capped CAPE reservoir over E-Germany due to strengthening 20-30 kn 850 hPa flow from the SE, so we would not be surprised about a severe cluster to turn more towards NE-Germany instead to N-CNTRL Germany. This activity poses all kind of hazard risks including large hail, severe wind gusts, heavy rain and an isolated tornado risk. Confidence in an upgrade to a level 2 is not yet high enough, but this area has to be monitored closely through the night.

... S-France ...

Ahead of a passing short-wave during the afternoon hours, onshore flow advects seasonable BL moisture north and beneath steep mid-level lapse rates. Those lapse rates diminish towards Switzerland and E-CNTRL France. Hence best CAPE remains confined to the level 1 area with 500-1000 J/kg MLCAPE forecast. DLS in the 20 m/s range and strong directional shear highlight a risk of organized multicells/isolated supercells with large hail, severe wind gusts, heavy rain and an isolated tornado threat. A growing thunderstorm cluster is forecast during the evening and overnight hours as a cold front approaches gradually from the W. Heavy rain spreads N and becomes also focused along the SW-Alps.

...Baltic States to E/S-Poland and the Carpathian Mountains...

The stalling synoptic-scale front serves as focus for CI during the day. Rich prefrontal BL moisture offsets meager mid-level lapse rates with widespread 1000-2500 J/kg MLCAPE (higher peaks towards the Carpathian Mountains).

CI is probable from the Baltic States to Poland with DLS around 10 m/s, so intense pulsating thunderstorms are forecast, which grow upscale into temporarily organized (cold pool driven) clusters. Initiating storms pose a large to isolated very large hail and severe wind gust threat with excessive rain becoming the dominant risk betimes. Regionally lowered LCLs and better LL shear next to the weak boundary could spark an isolated tornado event.
Towards the Carpathain Mountains missing foci for lift makes CI more questionable. However right now numerous mountain storms are still expected in a moderate to high CAPE and 20 kn DLS environment. Large/very large hail, severe downbursts and excessive rain are possible with any thunderstorm.

Despite the risk of concentrated severe and isolated extremly severe events, missing foci and mesoscale/orographic influences preclude a level 2 for now.

We also expanded a low confidence low prob lightning/level 1 all the way to Greece to account for isolated CI in a high CAPE/weak shear environment with isolated large hail, severe wind gusts and heavy rain.

...Turkey...

500-1000 J/kg MLCAPE and DLS of less than 10 m/s in a weakly capped environment point to slow moving and clustering thunderstorms with locally excessive rain the main hazard. A confined level 1 was issued where the highest risk of slow moving thunderstorm clusters is anticipated.

...Estonia into far W-Russia ...

A thinning warm sector with 1000-2500 J/kg MLCAPE is affected by DLS in the 10 m/s range. Uncertainty is high if this warm sector gets affected by ongoing convection from the previous night with latest radar data indicating a growing cluster over the Baltic States and over Estonia. Most models take both clusters to the N and E and therefore away from the warm sector, so at least temporal diabatic heating seems plausible. A passing wave to the W and both synoptic-scale cold and warm fronts serve as foci for scattered CI. A large cluster of thunderstorms is forecast to move E/SE during the day. As this cluster rides along the warm front / CAPE axis to the SE, near normal aligned 15 m/s 0-3 km shear vectors indicate the chance for a progressive MCS with swaths of severe wind gusts. More discrete thunderstorms bring large to very large hail, severe wind gusts, heavy rain and an isolated tornado threat. A level 2 upgrade was not performed due to limited time for recovery from the nocturnal convection, limited diabatic heating and weak/modest DLS.