Storm Forecast
Valid: Sun 22 Feb 2015 06:00 to Mon 23 Feb 2015 06:00 UTC
Issued: Sun 22 Feb 2015 04:01
Forecaster: TASZAREK

A level 2 was issued for S Italy mainly for tornadoes, large hail and severe wind gusts.

A level 1 was issued for Ionian Sea, parts of Adriatic and S Italy mainly for large hail, severe wind gusts and excessive precipitation.

A level 1 was issued for Britis Isles mainly for severe wind gusts of convective origin.

SYNOPSIS

Weather in Europe is driven by three main baric systems. High over most of E and SE Europe, windstorm with 950 hPa at the center approaching to NW Europe, and trough centered over C Mediterranean that is expected to bring most of the Sunday's severe weather phenomena associated with convection. Central, N and E Europe stays under influence of dry and cold polar air of continental origin. Marine moist and unstable air masses are located over central and E Mediterranean. Tongue of warm and moist air will be brought to W Europe by warm front approaching from the Atlantic. Three jet streaks will be present during the forecast period, first one over British Isles, second extending from France to Algeria, and the third one that overlaps with thermodynamic instability over C Mediterranean - extending from Tunisia to Turkey.

DISCUSSION

...Ionian Sea, parts of Adriatic and S Italy...

Weakening stationary trough centered over C Mediterranean will provide in its right bottom flank good overlap of cold air in mid-levels (which is a consequence of cut-off from the previous day) with low-levels warm and moist air that advects from S and SW. Such a pattern will produce lapse rates up to 8C/km that together with boundary-layer's mixing ratios up to 8 g/kg is expected to provide CAPE up to 1000 J/kg. Since instability region will overlap with jet streak from mid-levels, severe weather phenomena is expected during the whole forecast period in the right-bottom flank of the trough.

The best overlap of 500 J/kg CAPE (mixing ratios locally ~ 10g /kg) with LLS up to 10 m/s and DLS up to 25 m/s is forecast in the morning hours (06-12Z) over S Italy. Given also 0-3km SRH up to 250 m2/s2 and advection of absolute vorticity at 500 hPa, convection in such environment can organize into supercell thunderstorms that will be capable of producing tornadoes, large hail and severe wind gusts.

In the rest of the forecast period, most of the severe weather phenomena is likely to occur over waters of S Adriadic and Ionian Sea. Thunderstorms in the level 1 area will move northeastwardly and are expected to be active during the whole forecast period. Over coastal areas of S Italy and Balkan Peninsula excessive precipitation in the rich PW environment are not ruled out.

During the evening and nighttime hours good overlap of CAPE ~ 1000 J/kg and moderate QG lift over E Ionian Sea can result in high lightning activity. Possible line of storms will most likely move into W Greece coast in the end of the forecast period.

Limitation to this forecast is mostly related to not very supportive QG-forcing. The best overlap will occur in the morning hours over Sicilia and in the afternoon and evening hours over E Ionian Sea. Nevertheless, level 2 is issued due to favorable conditions for tornadoes in S Italy, that are possible, if supercells will occur.

...British Isles...

Deep cyclone with pressure at the center down to 950 hPa will move from Greenland to Scotland in the evening hours. Advection of cold polar air (-5C at 850 hPa) over warmer water areas will produce lapse rates up to 8C/km and provide thermodynamic instability measured by CAPE up to 200-300 J/kg. Wind flow in low and mid-levels is forecast to reach values of 20-25 m/s and thus such gusts are possible at the ground. NWP models compute that convection in this environment can enhance gusts even up to 30m/s. During the night and in the Monday's morning, rain will change into snow, thundersnow with stron wind in Ireland and Scotland is not ruled out. Although convection will occur, lightning activity will be rather marginal.