

535 

WWUS20 KWNS 201803

SEL8

SPC WW 201803

ARZ000-LAZ000-MSZ000-210100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 168

NWS STORM PREDICTION CENTER NORMAN OK

105 PM CDT WED APR 20 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       FAR SOUTHEAST ARKANSAS

       NORTHEAST LOUISIANA

       MISSISSIPPI



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 105 PM UNTIL

800 PM CDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 70

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES SOUTH OF

COLUMBUS MISSISSIPPI TO 60 MILES SOUTH OF MONTICELLO ARKANSAS.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU8).



REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.



DISCUSSION...TSTMS WILL INCREASE IN COVERAGE AND INTENSITY THIS

AFTERNOON ALONG SYNOPTIC COLD FRONT AND PRECEDING CONVECTIVE OUTFLOW

BOUNDARIES.  MODIFICATION OF 12Z JAN SOUNDING FOR CURRENT WARM

SECTOR CONDITIONS SUGGESTS THAT ENVIRONMENT IS ALREADY STRONGLY

UNSTABLE WITH MLCAPE OF AROUND 3000 J/KG.  WHEN COUPLED WITH THE

STEEP MIDLEVEL LAPSE RATES AND 30-40 KT OF DEEP WLY

SHEAR...ENVIRONMENT WILL BE SUPPORTIVE OF SUPERCELL AND ORGANIZED

MULTICELLS CAPABLE OF LARGE HAIL AND DAMAGING WIND GUSTS.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 27030.





...MEAD

