Storm Forecast
Valid: Sun 04 Jan 2015 06:00 to Mon 05 Jan 2015 06:00 UTC
Issued: Sun 04 Jan 2015 02:00
Forecaster: TASZAREK

SYNOPSIS and DISCUSSION

Synoptic patter in Europe is dominated by two large features: weakening trough over Russia and long ridge extending from Azores High up to N Scandinavia. This setup provide meridional position of Jet Stream with strong flow of dry and cold arctic air down to Balkan Peninsula. Although no favorable conditions for severe thunderstorm development are forecast, there is still a small chance for lightning activity in four regions.

While most of the western Europe will stay under the influence of high pressure that inhibit convection, marginal thunderstorm activity might be present in the zone of massive lowering of dynamic tropopause across central and southeastern Europe including Mediterranean Sea. NWP models forecast marginal instability (CAPE from 100 up to 300 J/kg) in the C Italy, Tyrrhenian and Adriatic Sea and parts of Greece and Albania. Convection in these regions may be supported by vorticity advection and cold front approaching from N and NE. Accompanied by impressive DLS (20 - 35 m/s) with mixing rations on the level of 6-8 g/kg and steep vertical lapse rates these conditions can result in isolated large hail phenomena. Due to relatively high 0-3km SRH values over Tyrrhenian Sea also some isolated supercell cannot be ruled out. Nevertheless probability is too limited to issue lvl. 1 threat, especially if we consider that the CIN value along W Italian coast is predicted to amount -100 J/kg.

During late night thunderstorms are also possible in the E Mediterranean where shallow low-level trough will develop in front of the approaching long wave with peak over Balkan Peninsula. Although convection will be shallow, some lightning should occur in the end of the forecast validity.

Marginal probability for lightning will be also present in the C Poland where isolated convective cells may develop in the zone of very strong vertical lapse rates (8-9 C/km) with rather limiting low-level moisture content (mixing ratio ~3 g/kg). Marginal instability of CAPE ranging from 50 up to 200 J/kg will overlap with strong low-level wind shear (10-15 m/s) and 0-1km SRH (100-150 m2/s2) potentially giving marginal risk for isolated tornado phenomena and severe wind gusts. Nevertheless, potential for convection will be too small to issue lvl. 1 threat. The main limiting factor is associated with rather insufficient lifting mechanisms in this area.

The last area where thunderstorms are possible is W Norwegian coast where trough located over N Norwegian Sea will push dry and cold arctic air masses over relatively warmer water and result in marginal instability ranging up to 200 J/kg. Convection forcing in this zone may be supported by orographic lifting mechanism and QG-forcing. Low level of LFC and LCL together with relatively low wind shear values cannot rule out waterspout phenomena along Norwegian coast.