Storm Forecast
Valid: Fri 21 Jun 2019 06:00 to Sat 22 Jun 2019 06:00 UTC
Issued: Thu 20 Jun 2019 18:57
Forecaster: GROENEMEIJER

A level 2 was issued for parts of Northwest Ukraine and South and Central Belarus for large hail, severe wind gusts and very heavy rainfall.

A level 1 was issued across parts of Finland, NorthWest Russia, Belarus, the Batlic States, Poland, Ukraine,
Czechia, Slovakia, Hungary, the northern Balkans, North Italy, the Alpine countries, Souht Germany, Southeast France and Northeast Spain for large hail, heavy rain and locally for severe wind gusts.

SYNOPSIS

A southwesterly flow persists over a large part of western, central and northern Europe. A trough initialy over Scotland moves to the northern Baltic Sea. Ahead of it, a surface cycloneshould develop over North Sweden. A fairly humid and warm air-mass resides over Finland, the Baltic States into central Europe. Within this air-mass, scattered to widespread storms are expected to develop on Friday, as low to moderate CAPE develops.

Upstream, a local vorticity maximum over the Bay of Biscay moves slowly eastward and reaches central France on Saturday morning. Isolated to scattered storms are expected to develop over Southeast France and Northeast Spain.

DISCUSSION

Finland, Russian Karelia...

In response to solar heating and some upward motion due to a minor shortwave trough, widespread storm initiation is expected across Western and Central parts of Finland. 500 - 1500 J/kg MLCAPE are predicted to develop with about 15 m/s unidirectional shear. This suggests that well-organized multicells and transient supercells are likely, which may produce some large (2-4 cm) hail, and local damaging winds along with heavy rain. The storms should increasingly cluster and move east into Russian Karelia.

Russian Leningrad, Vologda, Tver, Pskov, Novgorod oblasts, Southeast Estonia, Latvia, Lithuania, Belarus, West Ukraine, Poland, Czechia, Slovakia, Hungary, the northern Balkans, Austria...

In the aformentioned humid air-mass, about 1000-2000 J/kg MLCAPE are expected to develop, as a diffuse cold front moves eastward across the Blatic States and Poland. 0-6 km bulk shear is expected to be around 10 m/s across the entire region. NWP guidance suggests that scattered to widespread convection will initiate across this large region with only marginal large-scale forcing for lift. The amount of instability and shear should support well-organized multicells with a risk of 2-5 cm large hail and locally, severe wind gusts and very heavy rain.

It is difficult to pinpoint any favoured regions for higher severe weather probabilities, as those will depend on mesoscale details with low predictability. That being said, across Northwest Ukraine and South-central Belarus the best CAPE and shear overlap is forecast, with around 2000 J/kg and 15 m/s of 0-6 km bulk shear. Here, the risk of hail, severe wind gusts appears high enough to warrant a level 2.

NE Spain, SE France...

Ahead of the vorticity maximum moving east across southern France, large scale upward motion will aid the development of convection across these areas. Relatively strong bulk wind shear of 15-25 m/s in the 0-6 km layer suggests that a number of supercell storms may develop, e.g. over the Pyrenees, the mountains of NE Spain and possibly the southern Massif Central and th northern Apennines. With 1000-1500 J/kg of MLCAPE predicted, such storms will bear a risk of large (2-5 cm), and possibly even somewhat larger hail. A low-end risk of severe winds and heavy rain will also exist.

North Italy, Slovenia, North Croatia...

During the day storms that develop in these areas will do so in an environment with about 10 m/s of deep-layer shear. However, as the mid-/upper-level system from France approaches, shear forcing for upward motion will increase. As a result, scattered to widespread, likely somewhat elevated storms are expected during the late evening and night, that may be well-organized. They may bring some large hail and possibly also severe wind gusts and very heavy rain.

Alps...

Diurnally-driven storms are expected to become quite widespread in a weakly capped environment. Some risk of marginally severe hail and local heavy rainfall are forecast.

Turkey...

Widespread storms are extecped to initiate across the Turkish highland. Although some marginalyl severe hail or a very isolated severe wind gust cannot be discounted, the virtual absence of wind shear mitigates this risk to a large extent.

Sweden...

Near the surface cyclone that forms across Northland, a number of slow-moving storms will develop, that could pose a risk of high rainfall accumulations. The risk is deemed a bit too low to warrant a level 1.