Storm Forecast
Valid: Wed 23 Aug 2017 07:00 to Thu 24 Aug 2017 06:00 UTC
Issued: Wed 23 Aug 2017 07:07
Forecaster: PUCIK

A level 1 was issued for large hail and severe wind gusts over N Spain.

A level 1 was issued for excessive rainfall and tornadoes over N Russia.

A level 1 was issued for severe wind gusts over W Russia.

SYNOPSIS

Dominant synoptic-scale feature is a deep cyclonic vortex centered over the Baltic states, Belarus and Ukraine that is slowly shifting towards NE. Strong mid to upper tropospheric flow surrounds the vortex with windspeeds over 20 m/s. A short-wave trough will cross W Russia at its forward flank. To the west, a ridge will stretch from the Mediterranean towards BENELUX and the Northern Sea. A subtle short-wave is forecast to cross N Spain. Closer to the surface, a strong cold front will cross W Russia during the day while a warm front stretches over N Russia. A cold front is forecast to cross NW France and BENELUX overnight. DMC activity is forecast along the mentioned frontal boundaries and with the short-wave over Iberia. Scattered thunderstorms are expected also in the core of the cyclonic vortex, owing to the steep lapse rates under the cold mid-tropospheric airmass.



DISCUSSION

... N Spain ...

Isolated to scattered thunderstorms are forecast to form in the environment of steep mid-tropospheric lapse rates of over 7 K/km as the short-wave approaches. With moderate vertical wind shear, DLS around 15 m/s, well organised multicells may be capable of isolated large hail and/or severe wind gusts with inverted-V profiles below the cloud base.

... N Russia ...

Thunderstorms will be initiated by the isentropic ascent across the warm front in the southerly lower tropospheric flow. Forecast soundings show moderate CAPE values, between 500 and 1500 J/kg with high relative humidity in the whole vertical profile. This suggests a risk of heavy rainfall, especially if storm development anchors on the warm front with cell training. Furthermore, veering wind with height, LLS above 10 m/s and LCLs below 1000 m suggest a potential for tornado. This could be limited by the lack of high DLS supportive of sustained supercellular convection.

... W Russia ...

A line of thunderstorms is forecast to form along a fast moving cold front in an environment of 15 to 20 m/s shear parallel to the boundary. Such orientation of shear will promote a quick development of QLCS that may be capable of severe wind gusts. Limiting factor will be rather marginal nature of instability, with MLCAPE values only around 500 J/kg and the displacement of stronger lower tropospheric flow to the east of the advancing front.