Storm Forecast
Valid: Wed 29 Apr 2015 06:00 to Thu 30 Apr 2015 06:00 UTC
Issued: Tue 28 Apr 2015 20:39
Forecaster: PUCIK

A level 1 was issued for NW Russia mainly for severe wind gusts and tornadoes.

SYNOPSIS

Europe will generally be under a broad area of low geopotentials during the forecast period with numerous embedded troughs. The most prominent one will quickly cross the Baltic States towards the continent, inducing cyclogenesis over the Baltic Sea and S Finland. Especially warm and cold front of the deepening low may serve as foci for severe weather over NW Russia and this region will be covered in more detail below. Otherwise, isolated to scattered DMC is forecast with the other troughs, especially in their cores, where cold mid-level temperatures induce steeper lapse rates. However, chances of severe weather in the other areas with possible DMC will be very low, not warranting any Lvl.

DISCUSSION

... NW Russia ...

As mentioned above, sharp mid-tropospheric trough approaching the area will induce low-level cyclogenesis and should strengthen the low-level flow over the region. Models hint on 20 to 25 m/s of 850 hPa flow even in the warm sector. At the upper levels, stronger flow will be mostly deflected to the N of the warm front. Near the warm front, both strong DLS and LLS is forecast, while in the warm sector only strong LLS is simulated. Anyway, 10 to 15 m/s of LLS will cover a large extent of the warm sector. With rapidly approaching trough, potential will exist for a linearly organised system along the cold front with potential for severe wind gusts. Along the warm front, perhaps more discrete convection, including supercells, will be possible with threats of severe wind gusts and also tornadoes as LCL heights drop towards N.

There seems to be major discrepancy in models regarding the degree of destabilisation. While GFS simulates even over 1200 J/kg of CAPE locally, ECMWF simulates only patches of marginal latent instability. Main culprit could be the low-level moisture. Even at the time of forecast issuance, dew points over Russia are lower compared to the GFS predictions and it seems unlikely that as of Wednesday 12 UTC, 2 m dew points will reach values between 14 and 16 deg C. Due to these uncertainities, only Lvl 1 is introduced. However, in case that low-level moisture could indeed support higher CAPE values, more widespread severe weather would be possible.