Storm Forecast
Valid: Mon 22 Dec 2008 06:00 to Tue 23 Dec 2008 06:00 UTC
Issued: Sun 21 Dec 2008 21:17
Forecaster: TUSCHY

SYNOPSIS

A low-index/weak zonal flow pattern continues over Europe with strong ridging over W/NW Europe and a strengthening trough over E-Europe. Not much convective activity expected in this pattern.

DISCUSSION

... Lithuania and Latvia ...

Strong NW flow keeps weather conditions unsettled over the Baltic Sea and highlighted areas. Rapid cool-down of mid-levels well ahead of a southward pushing surface cold front creates an unstable atmosphere over a broad area. Most significant CAPE release occurs over the SE Baltic Sea during the morning hours as temperatures at 500hPa drop below -30°C and parcel layer depth increases rapidly. Despite meager chances for thunderstorms regarding climatology, the conditions look favorable for at least isolated activity and hence a general thunderstorm area was issued. Further inland, surface moisture becomes less which appeares in rapidly decreasing instability values. As another weak impulse passes by during the afternoon hours, a few thunderstorms could also develop further inland. The main risk will be gusty winds and marginal hail.

... N-/central Poland and NE/E-Germany ...

A very compact mid-level jet moves in from the NNW over NE-Germany and W-Poland. Forecast soundings indicate the chance for somewhat deeper convection over Poland as lapse rates at all levels steepen. Deep convection would be possible but right now not likely as boundary layer moisture values are low and cooling at mid-levels not as robust as further to the northeast. Models give no hint on convective precipitation, but the atmosphere remains moist especially over NE-Poland and a vorticity maximum crosses the area from the NW during the most favorable time of the day. For now, we did not issue any thunderstorm area as quality of the boundary layer looks too bad, but a very isolated thunderstorm could occur beyond the highlighted area over NE Poland.

NE-E Germany remains under the anticyclonic side of the jet and hence mid-/upper levels don't assist deep convection, but inversion height in the lower troposphere remains quite high ( e.g. above 800hPa). GFS constantly had some modest LL CAPE release and forecast soundings show the possibility of shallow convection. We don't want to exclude an isolated funnel event over extreme NE/E-Germany and NW/W-Poland during the early morning hours. This is a very low-end and short-lived threat.

... East of Crete ...

A strong upper trough drops southwards and a weak shear-moderate instability event unfolds for the highlighted area. The main risk will be an isolated waterspout, marginal hail and gusty winds.