Storm Forecast
Valid: Thu 30 May 2019 06:00 to Fri 31 May 2019 06:00 UTC
Issued: Thu 30 May 2019 05:56
Forecaster: GATZEN

A level 1 was issued for parts of south-western and western Russia mainly for large hail, severe wind gusts and excessive rain.

A level 1 was issued for western Russia and central Ukraine mainly for excessive precipitation and large hail.

A level 1 was issued for northern Turkey mainly for large hail.

SYNOPSIS

A stationary cut-off is centred over the Adriatic, where the mid-level temperature is below -20°C. South-west European ridging extends east across France and Germany into Poland, whereas the east Mediterranean and Balkans are affected by a cyclonically curved jet and embedded vort-maxima. A strong jetstream is located across northern Europe. At lower levels, most of Europe including the Mediterranean is affected by cold and rather dry air masses. Mixing ratios exceeding 10 g/kg can be found along a frontal boundary stretching from the west Black Sea to the central Ukraine northward into Russia, where the low-level moisture also overlaps with steeper 800-600 hPa lapse rates. Elsewhere, unseasonable weak lapse rates are present that slowly start to recover during the day.

DISCUSSION

South-western Russia into Ukraine

Latest satellite images indicate a band of clouds along the frontal boundary extending from the central Ukraine north-eastward into south-western and north-western Russia. Embedded thunderstorms are currently going on near the Belarus / Russia / Ukraine boarder triangle. Convective clouds can also be seen east of the boundary across Russia, where steep lapse rates are located. At low levels, surface dewpoints are around 15°C in this area.

With diurnal heating expected east of the boundary, latest models forecast substantial MLCAPE of 1000 to locally 2000 J/kg in the afternoon. Convection initiation is expected as the frontal boundary intensifies and starts to move south-west during the day. Warm air advection east of the frontal boundary and some DCVA at the right entrance of a mid-level jet will cause some large-scale lift as well.

Storms will form in limited deep layer vertical wind shear of 10-15 m/s over the lowest 6 km. Close to the boundary, where MLCAPE will still be around 500-1000 J/kg due to rich low-level moisture, deep-layer shear is between 15 and 20 m/s. With mostly straight-line low-level hodographs, main threat is multicells and some splitting storms near the boundary. However, storm motion vectors of right movers are mostly parallel to the frontal boundary and rapid clustering is expected along the cold front. Large hail seems to be the primary threat, with some wind and flooding events not ruled out. Along the northern portions of the risk area, stronger low-level vertical wind shear close to the cold front with up to 8 m/s in the lowest km may be favourable for low-level rotation and discrete storms could produce a tornado.

Farther east, isolated storms are forecast. With plenty of CAPE in the haul growth zone thanks to steep mid-level lapse rates, large hail is possible with any mature storm. Additionally, low-level inverted-v profiles promote a severe wind gust threat.

Storms will weaken after sunset with the severe potential also decreasing. Along the cold front, thunderstorms can survive the night.

Northern Turkey

A well-developed sea breeze front is expected to advect rich Black Sea moisture onshore, with upslope winds across northern Turkey. The low-level moisture overlaps with an elevated mixed layer spreading north-east with the mid-level flow. Diurnal heating can result in local MLCAPE build-up to 2000 J/kg. With large CAPE in the hail growth zone but limited vertical wind shear around 10 m/s in the lowest 6 km, we expect large hail with the stronger storms. Weak CAPE at low-levels seems to limit the potential of severe wind gusts today.