

726 

WWUS20 KWNS 222102

SEL4

SPC WW 222102

NEZ000-SDZ000-230400-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 684

NWS STORM PREDICTION CENTER NORMAN OK

400 PM CDT WED SEP 22 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       NORTHERN AND WESTERN NEBRASKA

       SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 400 PM UNTIL

1100 PM CDT.



TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 60 STATUTE

MILES NORTH AND SOUTH OF A LINE FROM 40 MILES EAST SOUTHEAST OF

YANKTON SOUTH DAKOTA TO 60 MILES SOUTHWEST OF MULLEN NEBRASKA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU4).



REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND 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.



OTHER WATCH INFORMATION...CONTINUE...WW 680...WW 681...WW

682...WW 683...



DISCUSSION...APPROACH OF UPSTREAM IMPULSE FROM THE CNTRL ROCKIES IS

EXPECTED TO SUPPORT AN INCREASE IN TSTMS LATE THIS AFTERNOON INTO

EVENING FROM VICINITY OF THE WARM FRONT OVER NRN NEB SWWD ALONG LEE

TROUGH INTO WRN NEB.  BASED ON 18Z LBF/20Z OAX SOUNDINGS...AMBIENT

AIR MASS IS MOIST AND MODERATELY UNSTABLE WITH MLCAPE OF 2000-3000

J/KG AND A DECREASING CAP.  THE STRONGEST LOW-LEVEL SHEAR AND

ASSOCIATED TORNADO THREAT IS EXPECTED ALONG THE WARM FRONT THIS

EVENING.  HOWEVER...SUPERCELLS CAPABLE OF A TORNADO OR TWO WILL BE

POSSIBLE WITH ANY STORMS THAT CAN DEVELOP AND BECOME SUSTAINED ALONG

THE LEE TROUGH.



AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

500. MEAN STORM MOTION VECTOR 25030.





...MEAD

