Message #19371

[martinastro]

From Skywarn UK...

SKYWARN UK SEVERE WEATHER WATCH #012
ISSUED: 0000UTC, WEDNESDAY 15TH DECEMBER 2010.

SKYWARN UK HAS ISSUED A SEVERE WEATHER WATCH FOR THE FOLLOWING REGIONS:
ALL REGIONS IN SCOTLAND
NORTHERN ENGLAND
NORTHWEST ENGLAND
EAST MIDLANDS
WEST MIDLANDS
EAST ANGLIA
WALES
NORTHERN IRELAND
SOUTHWEST ENGLAND

IN EFFECT FROM 00UTC ON THURSDAY 16TH UNTIL 1200UTC ON FRIDAY 17th DECEMBER 2010.

ARCTIC FRONT SURGING SOUTH, CONVECTIVELY UNSTABLE AND WITH VERY COLD AIR BEHIND.

THERE IS A POSSIBILITY OF SEVERE WEATHER AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO:
STRONG GUSTS...BLIZZARDS...HAIL...FUNNELS...TORNADOES...SNOW AND SURFACE ICING.

DISCUSSION:
USING A BLEND OF ECMWF, GFS AND UKMO NAE MODEL DATA; REGRESSING HIGH PRESSURE PATTERN IS ALLOWING AN AMPLIFIED TROUGH TO SURGE INTO NW EUROPE FROM THURS 00Z. VERY COLD ARCTIC AIR, WITH 850-1000HPA THICKNESSES DOWN TO 126 AND POSSIBLE 504DAM UPPER GEOPOTENTIAL HEIGHTS. JET STREAM IS NW'LY OVERRIDING A SPLIT SURFACE FRONT CREATING POSITIVE VORTICITY AND 3-400M2S2 0-3KM SHEAR THROUGH SCOTLAND, WALES AND ENGLAND 00-12Z, IRELAND AND THE SW 09-15Z. PRECIPITATION WILL BE RAIN INCREASING AND BECOMING SQUALLY WITH CONVECTIVE ENHANCEMENT, THEN BRIEF HEAVY SNOW AND BLIZZARDS ALONG THE SECONDARY FRONT. SNOW SHOWERS BEHIND WILL ADVECT INLAND AROUND NW AND W SCOTLAND, NORTHERN IRELAND AND WALES AND COASTS OF NW, NE AND SW ENGLAND. WINDS STRENGTHENING TO 40KT ALONG THE FRONT WITH POTENTIAL FOR ENHANCED CONVECTIVE GUSTS, BOWING LINE SEGMENTS AND MID-LEVEL VORTICES LEADING TO POSSIBLE BRIEF TORNADOGENESIS. THERMALLY FORCED CONVECTION AHEAD OF THE FRONT, AND DYNAMICALLY FORCED CONVECTION LIKELY ALONG AND BEHIND IN SHOWER TRAINS, WITH THE ADDED RISK OF HAIL AND LIGHTNING.

SPOTTER ACTIVATION IS REQUESTED AND SPOTTERS ARE REQUESTED TO REPORT SNOWFALL ACCUMULATIONS AND ALL FACTORS EXCEEDING ACTIVATION CRITERIA