WX: UK: Severe Thunderstorm Watch – Monday 7th May 2012

UK SEVERE THUNDERSTORM WATCH #018
ISSUED: 0130UTC MONDAY 7TH MAY 2012 (GJ/SM)

EVERE THUNDERSTORM WATCH FOR THE FOLLOWING REGIONS:
WALES
NORTHERN ENGLAND
MIDLANDS
SOUTHWEST ENGLAND
SOUTHEAST ENGLAND
NORTHERN IRELAND
WESTERN SCOTLAND

IN EFFECT FROM 1000UTC MONDAY 7TH UNTIL 0200UTC TUESDAY 8TH MAY 2012

MATURING LOW WITH AN UNSTABLE WARM SECTOR AND FAVOURABLE SHEAR FOR ORGANISED CONVECTION

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:
HEAVY RAIN…STRONG GUSTS…FUNNELS/WEAK TORNADOES…HAIL…FREQUENT LIGHTNING…FLASH FLOODING

DISCUSSION:
THERE IS GOOD MODEL AND METEOROLOGICAL AGENCY CONFIDENCE OF A POSSIBLE SEVERE THUNDERSTORM RISK THROUGH MONDAY AFTERNOON AND EVENING. AN OCCLUDED WARM FRONT CROSSES THE UK DURING THE MORNING, STALLING OVER SCOTLAND BY END OF THE AFTERNOON, WITH THE LOW CENTERING OVER IRELAND. NEAR THE CENTRE OF THE LOW, STEEP LAPSE RATES WILL AID STRONG CONVECTION AND SLOW MOVING THUNDERSTORMS PERSISTING INTO WESTERN SCOTLAND THROUGH TO LATE EVENING WITH LOCALISED ACCUMULATIONS OF UP TO 20MM IN SHORT PERIODS. ACROSS WALES AND SOUTHWEST ENGLAND, PERSISTENT OROGRAPHICALLY TRIGGERED CONVECTION MAY LEAD TO SUCCESSIVE PERIODS OF HEAVY RAIN WITH SIMILAR ACCUMULATIONS BY THE END OF THE PERIOD. LOW LEVEL SHEAR ACROSS THESE AREAS, ALONG WITH THE MIDLANDS AND NORTHERN ENGLAND, WILL INCREASE THROUGH THE DAY WITH CONVERGENT SURFACE WINDS BECOMING THE FOCUS FOR STRONGER CONVECTION INTO THE SECOND HALF OF THE AFTERNOON AND EVENING, POSSIBLY ORGANISING STORMS AND MAXIMISING THE CHANCE OF DETAILED THREATS. DEEP LAYER SHEAR INCREASES DURING THE PERIOD WITH THE DIVERGENT NOSE OF A CYCLONIC JETSTREAM PUSHING ACROSS THE WARM SECTOR ALONG WITH INCREASING MID TO UPPER LEVEL LAPSE RATES, SUPPORTING STRONGER AND SUSTAINED CONVECTION PARTICULARLY FOR WALES AND THE MIDLANDS. ACROSS THE SOUTHEAST OF ENGLAND, CONVECTION INITIATED OVER NORTHERN FRANCE MAY DEVELOP AND TRANSIT AS A CLUSTER OF STORMS DURING THE EVENING. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY. THIS WATCH MAY BE UPGRADED.

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