Storm Forecast
Valid: Mon 05 Dec 2011 06:00 to Tue 06 Dec 2011 06:00 UTC
Issued: Sun 04 Dec 2011 18:25
Forecaster: TUSCHY

SYNOPSIS and DISCUSSION

A well structured branch of the polar vortex extends far to the south and covers or influences most parts of Europe. This pattern allows a fairly dry air mass to overspread a vast part of our forecat area, keeping overall thunderstorm probabilities limited.

One area with augmented DMC chances will be atop the North Sea, as temperatures at 500/850 hPa drop below -35/-5 °C respectively. SSTs increase from north to south with values of 10-13 °C. EL temperatures remain at or below -30°C, which assists in augmented ice/graupel pellet production, favorable for some charging/lightning production...probably again more sporadic in nature. Also, patches of better SBCAPE build-up are forecast and forecast soundings reveal some better CAPE dispersal in the aforementioned graupel/ice zone, so a fairly coarse low-end lightning probability area seems to be justifiable. We expand the lightning area well inland, as some time is needed for BL moisture to mix out, resulting in decreasing CAPE/updraft strength. Winds remain modest in strength, so strong wind gusts and marginal hail/sleet will be the main hazard.

A second area of interest will be the Adriatic Sea, as a lee cyclogenesis gradually consolidates. This depression remains quite diffuse and re-develops its center numerous times with significant model spread regarding placement/timing/strength. This feature starts to drop to the S/SE during the forecast, affecting all of the Adriatic Sea.
High resolution model data indicates pure onshore flow with missing coastal convergence signals. However, as mid-levels start to cool down, some moisture flux convergence along the coast seems to be more than adequate for some MLCAPE build-up in the range of roughly 500 J/kg. Repeatedly developing showers/thunderstorms are forecast along the E-part of the Adriatic Sea. There are some indications, that training may occur with some storms and hence a heavy rainfall risk exists along the E-coast of the Adriatic Sea. However, no model indicates excessive rainfall, which would match our level criteria. Also, marginal hail may accompany those storms, which take profit of strong DLS. Overall thunderstorm activity shifts to the south during the night with an ongoing heavy rainfall risk.

Sporadic storms may also occur over the E-Tyrrhenian Sea, E-Ionian Sea, E-Aegean Sea and the Gulf of Finland. No severe risk is anticipated with that activity.