Storm Forecast
Valid: Fri 02 Jan 2015 06:00 to Sat 03 Jan 2015 06:00 UTC
Issued: Thu 01 Jan 2015 13:20
Forecaster: TUSCHY

A level 1 was issued for parts of the Baltic Sea, Lithuania, Latvia, Estonia, S-Finland and NE Poland mainly for severe wind gusts. Onshore areas also see an isolated tornado/large hail threat.

SYNOPSIS and DISCUSSION

A strong extratropical cyclone is centered along the border Norway/Sweden at 06Z. Rapid deepening from the previous night levels off, although some more deepening is still anticipated during the forecast. This severe cyclone crosses Finland during the afternoon hours onwards.
Models show an overlap of an eastward pushing dry slot over the surface cold front during its passage over the Baltic Sea. A line of shallow convection can't be ruled out despite unfavorable placement in the right exit of a 60 m/s mid-level jet. 30 m/s near BL flow indicates severe gust potential with that convection. Onshore moving convection could cause an isolated tornado event from NE Poland to S-Finland, where enhanced SRH and weak LLCAPE overlap. A level 2 seems too much due to the broken/spotty nature of this line and rather shallow convection. Still, GFS indicates a low-end chance for temporarily deeper updrafts over Lithuania and Latvia, so we can't rule out shallow supercell structures. Large hail and an isolated tornado would be the main risk beside damaging wind gusts. The risk remains too blurred in model data for a level 2. Better mid-level instability towards W-Belarus indicates a chance of more elevated convection (atop a cooling BL due to the diurnal cycle). Hence we stopped with the level area along the border but kept the lightning area going more to the east.

LL winds substantially increase in the postfrontal air mass over parts of N-Sweden/Baltic Sea during the day, as wrap-around occlusion approaches from the west with 850 hPa winds aoa 35 m/s. Damaging wind gusts won't be accompanied by DMC and therefore will be excluded from our level scheme.

A broad lightning area was issued for offshore regions over the N-North Sea, with very cold mid-levels atop the warmer SSTs. Forecast soundings show chances for adequate graupel production that even an high probability area for lightning was issued (despite arguing with climatology). Marginal hail and strong wind gusts will be the main risk.

A few non-severe thunderstorms occur over the SE Mediterranean with decreasing activity during the forecast period.