Storm Forecast
Valid: Thu 18 Jul 2019 07:00 to Fri 19 Jul 2019 06:00 UTC
Issued: Thu 18 Jul 2019 07:25
Forecaster: GATZEN

A level 1 was issued for north-eastern Spain mainly for large hail.

A level 1 was issued for northern Italy, the eastern Alps, and northern Balkans mainly for large hail and excessive precipitation.

A level 1 was issued across Turkey and the eastern Black Sea region mainly for large hail.

A level 1 was issued for Belarus and western Russia mainly for excessive precipitation and to a lesser extent large hail and tornadoes.

A level 1 was issued for central Finland mainly for excessive precipitation.

A level 1 was issued for Scotland mainly for tornadoes.

SYNOPSIS

Low geopotential is present across eastern Europe, with an intense mid-level vortex centered over western Russia. A small embedded vortex across Czechia moves east. Low geopotential also extends into parts of the Mediterranean, with a short-wave trough axis from eastern Poland to southern France that progresses east today. Weak ridging is located across southern Scandinavia ahead of a North-Atlantic trough. A strong mid-level jet is directed towards The Channel between the Atlantic trough and a strong ridge that extends across the Iberian Peninsula. At low levels, a cold front moves into the central Mediterranean where weak cyclogenesis is expected as the mid-level trough advances. A weak frontal boundary also forms across the northern Balkans. North-western Russia is affected by an occluded front. Northwest of this low, a convergence zone extends across Finland. Western Europe is crossed by a cold front that enters Germany and France late in the period. Finally, thermal lows will form across Iberia and Turkey, causing well-developed convergence zones near the coastlines.

DISCUSSION

Northern Italy

Due to cyclogenesis over the central Mediterranean, an easterly low-level flow evolves across northern Italy. Latest models indicate a moist boundary layer and moderate lapse rates, so that some diurnal heating can result in about 1000 J/kg MLCAPE. Weak capping ahead of the approaching short-wave trough and low-level convergence will support initiation of further storms during the day. Weak deep-layer shear will limit storm organization. Expect some stronger storms due to low-level veering profiles and slightly increasing deep-layer shear to about 10 m/s, locally maybe 15 m/s in the afternoon and evening. Large hail will be the main threat, together with excessive precipitation due to the slow storm motion. A brief tornado cannot be ruled out if pre-existing vorticity is stretched by some storms.

Eastern Alps and northern Balkans

Steep lapse rates and rather moist low-level air masses are present, with MLCAPE around 1000 J/kg expected. CIN will be weak ahead of weak mid-level vortices that move eastward across the northern Balkans, northern Italy, and Czechia and Slovakia. Storms are expected to form in response to mountain-valley circulations and sea-breeze convergence lines. Slow moving storms with rather weak cold pools due to the moist boundary layer will pose a threat of excessive precipitation. Additionally, deep-layer shear between 10 and 13 m/s may support some better organized storms capable of producing large hail and severe wind gusts.

Western Russia, Belarus, Finland

Moist air masses are present over this region that is affected by the intense mid-level vortex across western Russia. An occlusion wraps around the trough center, associated with precipitation and embedded elevated thunderstorms across north-western Russia. To the north-west, some diurnal heating will result in surface-based CAPE across Finland where a convergence zone intensifies during the day. Storms that form will profit from strong southerly mid-level flow at the eastern flank of a mid-level trough across central Scandinavia. Deep-layer shear may exceed 15 m/s, supporting multicells and brief supercells, capable of producing large hail and severe wind gusts. Additionally, storms can move almost parallel to the low-level convergence zone with repeating storms in the same area, so that locally, excessive precipitation is not ruled out.

Over Russia and Belarus, main severe potential is expected south of the mid-level trough, where surface-based instability is expected to develop. Excessive rain potential is expected due to slow storm motion and moist, skinny CAPE profiles. Later in the period, strong northerly flow evolves near the Belarus-Russian border with increasing low-level shear. A brief tornado is not ruled out although storm coverage will already decrease.

Over the southern portions of the level 1 across Russia, stronger deep-layer shear is forecast in combination with a few 100 J/kg MLCAPE. Storms may organize capable of producing some large hail. Overall threat is expected to be rather marginal, though.

North-eastern Spain and southern Turkey

Along the sea-breeze convergence zones, storms are expected to form today. MLCAPE around 1000 J/kg and deep layer shear between 10 and 15 m/s can support some organized storms capable of producing large hail and locally excessive precipitation.

Scotland

An intense short-wave trough crosses Scotland today associated with low-level stretching and lapse rate increase. Although low-level moisture is limited, some surface-based CAPE is forecast. Storms may develop over the land due to some insolation, and low-topped storms may be capable of producing a few tornadoes due to strong low-level vertical wind shear.