Storm Forecast
Valid: Fri 10 Jun 2016 06:00 to Sat 11 Jun 2016 06:00 UTC
Issued: Thu 09 Jun 2016 22:17
Forecaster: TUSCHY

A level 1 was issued for NE-Spain and SW France mainly for isolated large hail and isolated excessive rain.

A level 1 was issued for the Ionian Sea, the SE Adriatic Sea, all the way to NW Greece and Serbia mainly for excessive rain and a few tornado events. A spotty large hail event is possible.

A level 1 was issued for NE Poland, W-Belarus all the way to Latvia mainly for isolated severe wind gusts, large hail and a tornado event or two.

A level 1 was issued for parts of the Ukraine and far SW Russia mainly for isolated large hail and isolated excessive rain.

A level 1 was issued for parts of E-Finland mainly for and isolated tornado event and isolated excessive rain.

SYNOPSIS

Low-index pattern continues over Europe as numerous stable waves cross W/SE-Europe from NW to SE. The first wave exits the Bay of Biscay until noon and affects France until 06Z. Downstream progressive short-wave ridge amplifies north from Italy to the Alps and enhances mid-tropospheric height gradients towards a pronounced trough over NE Europe. As a consequence, a 30 m/s 500 hPa speed maximum travels from Denmark to Poland and to the far W-Ukraine unitl 06 Z. Another stable wave over the Ionian Sea shifts east, broadens and covers most of the Aegean / Black Sea and Turkey.
Out of a positive tilted trough over NE Europe, two separate vortices evolve over NE Europe with the southern and stronger one dropping from the Baltic Sea to Belarus until 06 UTC. Given disturbed flow pattern, various smaller scale mid-level waves traverse many parts of Europe which also adds a localized thunderstorm risk to various places. Therefore, numerous broad lightning areas were once again issued.

Low-tropospheric pressure gradients remain weak over most areas, despite the Baltic Sea and surroundings, where aforementioned strengthening mid-level vortex induces BL pressure fall. A LL vortex over the S-Baltic Sea deepens by roughly 5 hPa as is moves towards Estonia. The deepening cyclone results in sharpening warm and cold fronts wich push north/east respectively.

DISCUSSION

... Parts of Poland, W-Belarus, Lithuania and Latvia...

Strong DPVA overspreads the highlighted area from west and combined with a sharpening cold front, deep lift is forecast. Moisture recovery behind a departing frontal system from the previous day is marginal at best, but with strengthening ageostrophic flow in response to the deepening cyclone, a confined moisture tongue is expected to surge N/NE...just ahead of the eastbound moving cold front. Forecast soundings reveal weak mid-level lapse rates, partially offset by aforementioned BL moisture. Hence, 200-600 J/kg MLCAPE is forecast to cause scattered thunderstorms. Strongest kinematics occur from NE Poland to Estonia, where veered profiles are forecast. Combination of LCLs below 1000 m and enhanced LL shear/SRH-1 favors an isolated tornado event in the level 1 area. Stronger updrafts may be capable of producing isolated large hail. Betimes, a forced line of convection is expected along the cold front with swaths of strong to isolated severe wind gusts and hence the level 1 was expanded far east.
With 15 m/s DLS occuring far S, the level 1 was expanded all the way to E-CNTRL Poland mainly for isolated large hail.

The warm sector over Belarus features low BL moisture, which should suppress CI in the warm sector. Forecast soundings show a very dry sub-750 hPa layer with meager lapse rates atop. Initiation is unlikely, but in case of an elevated storm or two along the warm front, a localized severe downburst event would be the main hazard. This scenario was not reflected in probabilities due to low confidence.

During the night, isolated to scattered thunderstorms are forecast over the SE-Baltic Sea, as -30 °C at 500 hPa cross that area. An isolated waterspout event can't be ruled out with steepening LL lapse rates and relaxing LL shear.


Else, confined regions with somewhat enhanced severe are highlighted by numerous level 1 areas:

... NE Spain and SW France ...

Eastbound moving short-wave grazes N-Spain during the forecast. A 20 m/s mid-level jet crosses the Pyrenées, where locally steep mid-level lapse rates support up to 800 J/kg MLCAPE. A few large hail reports are possible. The level 1 was expanded north to SW France, where 700 hPa winds increase to 15 m/s. Combined with 400-800 J/kg MLCAPE, isolated large hail is possible next to heavy/isolated excessive rain with clustering storms.

... Ionian and Adriatic Sea to Serbia and parts of Greece ....

Departing mid-level wave leaves a very moist air mass behind. Progressive ridge moves in from the W, so S-Italy and the Ionian Sea wil only see favorable conditions for CI until 15-18 UTC. Further north, prolonged period with cyclonically curved flow induces enhanced probabilities for CI all day long. Rich low-tropospheric moisture offsets weak mid-level lapse rates (roughly 7K/km), so widespread 400-800 J/kg MLCAPE is forecast with up to 1 kJ/kg over Serbia. Weak DLS precludes organized convection, but pulsating and slow moving storms bring a chance for locally excessive rainfall amounts and locally severe wet downbursts. Forecast soundings show substantial LLCAPE along the E-coast of the Adriatic Sea extending all the way to W-Serbia /NW-Greece. There, numerous funnel/isolated tornado events are possible. Convection gradually diminishes during the night.


... W-Ukraine ...

Moisture pooling along a decaying front results in enhanced BL moisture. Once again, mid-level lapse rates remain modest at best, but 400-800 J/kg MLCAPE and veered 10-15 m/s deep-layer flow support a few organized multicells with marginal/isolated large hail. Stronger backing of the LL flow along the front itself combined with low LCLs may favor an isolated tornado event. The main risk will be locally excessive rain as storms grow upscale into numerous clusters.

... CNTRL Finland to the White Sea ...

A SW-NE aligned convergence zone will serve as focus for scattered thunderstorms during the 11-19 UTC time frame. Forecast soundings show 15 m/s DLS with veered flow, so we would not be surprised to see a few better organized thunderstorms as day progresses. Low LCLs and 100-150 J/kg LLCAPE point to an isolated tornado risk. Heavy rain may prompt flash flood problems on a local scale. Thunderstorms decay until midnight.

... CNTRL UK ...

Robust LL CAPE up to 150 J/kg, numerous LL convergence zones and low LCLs create a favorable set-up for isolated funnel/short-lived tornado events around peak heating and until sunset. Confidence in placement of those convergence zones was not high enough to go with a level 1 however.