Storm Forecast
Valid: Tue 21 Jul 2020 06:00 to Wed 22 Jul 2020 06:00 UTC
Issued: Mon 20 Jul 2020 21:56
Forecaster: DAFIS

A level 2 was issued for parts of W Russia and Georgia for large hail, severe wind gusts and tornadoes.

A level 1 surrounds the level-2 area for the same threats and also includes NE Turkey.

A level 1 was issued for parts of E Austria, Slovakia, N Hungary, N Romania, Ukraine, Belarus, Lithuania, Latvia, Esthonia and W Russia mainly for severe wind gusts and excessive precipitation, and to a lesser extent large hail.

A level 1 was issued for E Portugal, Spain, Andorra, and France for large hail and severe wind gusts.


SYNOPSIS

Several waves can be found in the analyses of upper-troposphere, but low-level baroclinicity remains weak, apart from the most-eastern parts of the continent. The unseasonably cold conditions in NW Europe will continue during this outlook, while a trough is crossing the North Sea and cold/dry air masses limit convective instability. More favorable conditions for convection exist more to the east, where the remnants of two cut-off lows are surrounded by short-waves and PVA, and below them we find unstable air masses. Another cut-off low is approaching the Iberian Peninsula and will provide synoptic lift to rather unstable air masses and will also increase the mid/upper-level flow and we expect DMC in Iberia as well as in South France.

DISCUSSION

.... Central and Eastern Europe ....

The trough over North Europe is propagating east during this outlook and is associated with a developing surface cyclone over Scandinavia. The cold front will cross the southern parts of Scandinavia, North Germany and Poland early in the morning on Tue 21/07, moving fast east, and during maximum solar heating we expect storms to initiate along the boundary line. Storms will also develop in the warm sector more to the east, but DLS will be weaker and the main convective mode should be isolated pulsating and non-severe storms. With a level-1 area we enclose the areas where a few large hail and severe wind gust events are expected. In addition, some areas in Belarus, Ukraine and W Russia will experience 2 rounds of thunderstorm activity, the first will be due to thermally driven convection, and the second during the cold front crossing and flash floods cannot be ruled out (PWAT >30 mm).

In SE Ukraine, W Russia, Georgia, and parts of NE Turkey, a strong wind flow increases DLS to 20-25 m/s, overlapping with high CAPE values. The area will experience strong positive vorticity advection and synoptic lift can lead to a few severe storms. All kinds of severe weather are expected, even tornadoes and waterspouts in the Black Sea coasts. A level-2 area covers the areas where the severe weather threat is maximized.


.... Spain, Portugal, Andorra and France ....

A WAA is forecast on Tue 21/07 over the Iberian Peninsula, with temperatures exceeding 26oC and 36oC at 850 hPa and at the surface respectively. Resulting steep lapse rates and low-level moisture mostly originating from marine areas close to the coasts during strong sea-breeze, will create a few hundreds of MLCAPE, locally exceeding 1500 J/kg. Although the low-level air masses close to the coasts will be strongly capped, CI can be achieved in mountainous areas where NWP models show a few storm cells developing after the maximum diurnal heating. In addition, the approaching cut-off low with PVA will provide additional lift, so CI is almost certain in Portugal, Andorra, and Spain. Any developing storm will be able to produce large hail given the high NCAPE values and severe wind gusts are expected due to high delta-theta-e values in the forecast fields.

In South France CI will also be difficult in the plains and close to the coasts, since the low-level unstable air masses must overcome the cap between 900 and 750 hPa. Nevertheless, there is a consensus from all the available NWP models about the development of more than 1500 J/kg MLCAPE and locally more than 2000 J/kg MUCAPE and CI in mountains should lead to a few storms in the afternoon. High CAPE, DLS in the range 14-18 m/s and steep lapse rates will create a favorable environment for large hail (larger than 2 cm) and severe wind gusts. Moreover, low-level veering winds, between 0-3 km will create strong helicity and storms may fast evolve into supercells. Convective activity may continue during the night and early morning of Wed 22/07.