Storm Forecast
Valid: Sun 18 Jan 2015 06:00 to Mon 19 Jan 2015 06:00 UTC
Issued: Sun 18 Jan 2015 02:06
Forecaster: TASZAREK
A level 2 was issued for parts of Sicilia and Italy mainly for tornadoes, large hail and severe wind gusts.
A level 1 was issued for Sicilia and S Italy mainly for large hail.
A level 1 was issued for C Italy, parts of Croatia, Bosnia, Macedonia and Albania mainly for excessive precipitation in Dinaric Alps and Apennines.
SYNOPSIS
Most of the European continent will remain under dry and cold airmass of polar origin. Warmer and moist airmass will be located as usually in the SE part of Europe. The intrusion of airmass with similar characteristics will take place over W and S parts of Iberian Peninsula.
In the forecast period a large long-wave geopotential pattern with axis extending from coastal zone of Algeria to Scandinavia will move eastward. Undulation at the tip of this pattern will result in two peak troughs. The first one associated with short-wave will pass through Sicilia, S Italy and Balkan Peninsula and create favorable conditions for severe convective storms.
Second low-level trough will move from Portugalian coast to Balearic Islands and slightly amplify from 1010 to 1005 hPa. This patter will bring thunderstorms to Moroccan coast and provide advection of cold airmass (0 C at 850 hPa) up to Algieria. Jet streaks will extend from Ireland to Portugal, and from Poland to Siberia.
DISCUSSION
...S Italy, Sicilia, parts of Greece and Albania...
Dangerous setup in this region is expected to bring severe weather of convective origin in the late afternoon hours. Southerly flow of relatively warm and moist air (mixing ratios up to 10 g/kg) will overlap with steep lapse rates that will result from SW flow of cold air in mid-levels. Such overlap creates instability measured by CAPE up to 1000 J/kg with cloud top temperatures below -30 C. Mentioned region will run under an impressive QG-forcing of short-wave origin. Dynamic flow of air in mid and low levels is expected to provide DLS > 20m/s and 0-3km shear > 10m/s. In such conditions convection is likely to organize into line of storms and also dangerous squall line capable of producing severe wind gusts. A level 2 in the forecast denote region where the possibility for such a feature will be the highest. Due to vertical directional shear few embedded and/or isolated supercells are possible with which large hail up to 4-5cm is possible. Orographic lifting over Sicilia and S Italy may intensify such features. In the lower troposphere dangerous overlap of LLS ~ 10m/s, 0-1km SRH ~ 150-250 m2/s2 and low levels of LCL and LFC provide good conditions for supercell tornadoes that if occur, may be likely to reach significant intensity. Although PW parameter is not very high, some local flash flood phenomena resulting from rich-boundary layer moisture and possible supercells cannot be rulled out.
The line of storms is expected to occur over Sicilia in the afternoon hours, and move north-eastwardly. Its intensity should decrease during night when reaching coast of Albania and Greece.
Limitations for this forecast are associated with uncertain intrusion of dry and warm air from Sahara that by providing capping-inversions may inhibit convection. Current NWP modes forecast this intrusion S from level 2 area ensuring good conditions for severe convective storms over Sicilia and S Italy.
...C Italy, parts of Croatia, Bosnia, Macedonia and Albania...
SW flow of moist, warm and unstable airmass sector with mixing ratios up to 7 g/kg and PW ~ 20mm combined with strong orographic lifting is expected to produce large amounts of precipitation on the slopes of Dinaric Alps and Apennines. Sum of precipitation can locally reach up to 200mm during the forecast period.
... NW parts of Europe ...
Uninterrupted in the last few days advection of cold and dry air over much warmer waters of North Sea results in impressive lapse rates (~ 7-8 C/km) that provide CAPE up to 200 J/kg. Although convection in such cells is shallow, cloud top temperatures below -20C with overlap of favorable QG-forcing create small probability for lightning. Waterspouts along the coasts are not ruled out.
...parts of Portugal and Spain, coast of Morocco...
Cold front associated with trough located over Portugal will push in the late morning convective line to the coast of Morocco.
Although large-scale forcing will be present, shallow convection and warm cloud tops will provide only small probability for lightning. Increased value of PW together with relatively slow motion of convective cells may create marginal threat for excessive precipitation phenomena. However, because the risk is very small and mainly correspond to marine area, no level threats are issued for this regions.
