Storm Forecast
Valid: Wed 18 Nov 2015 06:00 to Thu 19 Nov 2015 06:00 UTC
Issued: Wed 18 Nov 2015 06:25
Forecaster: PUCIK

A level 1 was issued for a belt from N UK towards Denmark, N Germany, Poland, W Ukraine and W Belarus for severe wind gusts and to the lesser extent for tornadoes.

SYNOPSIS

In the strong zonal flow, individual deep low pressure systems are making its way across Europe to the east. The first one, centered over the Baltic Sea will affect especially Poland and the Baltic States, filling up after it makes it onshore and continues to Russia. Another one will affect British Isles today and then overnight to Thursday also N Germany and NW Poland. With southern Europe being dominated by a large ridge, DMC activity will be tied to the aforementioned deep lows, in low CAPE - high shear situation.

DISCUSSION

... Poland to W Ukraine and Belarus ...

00 UTC Bergen sounding sampled the thunderstorm environment overnight in Germany with intense low-level shear and around 200 J/kg of CAPE. However, subsidence in the layer around 600-700 hPa resulted in stable layer near 700 hPa that DMC may be unable to panetrate in some cases. Broken bands of weakly electrified DMC are now moving over Poland with primary threats of severe wind gusts as 850 hPa windspeeds reach or even exceed 30 m/s. Lack of windshift line or isolated supercellular convection makes tornadoes less likely than straightline winds in this case. As left exit region of mid-level jet becomes less pronounced and system moves into less low-level moisture, threat will slowly diminish during the day as bands of DMC move towards W Ukraine and W Belarus. Lvl 1 seems to be sufficient for this situation.

... N UK towards Denmark, N Germany and NW Poland ...

In the zone of the left-exit region of the jet that will rapidly progress ESE-wards during the day, bands of DMC are forecast to develop. Again, very strong LLS is forecast so that storms will be capable of severe wind gusts. A level 2 was considered for this situation especially for N UK. However, NWP suggests that the plume of steep lapse rates will be somewhat decoupled from the tongue of best low-level moisture ahead of the cold front. This may be because the left-exit region lags a bit behind the surface cold front. In case that exit region with steeper lapse rates managed to overrun the warm sector, an electrified strongly forced convective line capable of swath of severe wind gusts and perhaps tornadoes (as SREH is higher in the warm sector) would be likely. Currently, more likely scenario seem to be bands of DMC behind the cold front with threat of isolated severe wind gusts. Overnight, DMC will reach also N Germany and N Poland. Over N Germany, coupling of the left exit with the warm sector and moister airmass seems to be more likely than over UK.