SEL9
   
   URGENT - IMMEDIATE BROADCAST REQUESTED
   SEVERE THUNDERSTORM WATCH NUMBER 819
   NWS STORM PREDICTION CENTER NORMAN OK
   245 PM CDT TUE SEP 14 2004
   
   THE NWS STORM PREDICTION CENTER HAS ISSUED A
   SEVERE THUNDERSTORM WATCH FOR PORTIONS OF 
   
          CENTRAL AND WESTERN IOWA
          EASTERN NEBRASKA
   
   EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 245 PM UNTIL
   1000 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 ALONG AND 75 STATUTE MILES
   NORTH AND SOUTH OF A LINE FROM 25 MILES SOUTH OF COLUMBUS NEBRASKA
   TO 30 MILES SOUTHEAST OF MASON CITY IOWA.
   
   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...STRONG BAROCLINIC ZONE HAS BECOME ESTABLISHED IN A
   SW-NE ORIENTATION ACROSS THE REGION THIS AFTERNOON...WITH
   TEMPERATURES IN THE LOWER 90S ACROSS WARM SECTOR.  FURTHER HEATING
   AND CONVERGENCE INVOF SURFACE FRONT WILL ALLOW ONGOING...ELEVATED
   CONVECTION TO BECOME INCREASINGLY ROOTED IN THE BOUNDARY LAYER WITH
   OTHER STORMS DEVELOPING AND MOVING NEWD THROUGH THE EVENING.  DEEP
   LAYER SHEAR IS SUPPORTIVE OF SUPERCELLS...MAINLY ACROSS NRN PORTION
   OF WW...HOWEVER PRIMARY SEVERE THREAT EXPECTED TO BE LARGE HAIL AND
   DAMAGING WINDS AS ACTIVITY BECOMES MORE MULTICELLULAR IN NATURE.
   
   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 23035.
   
   
   ...EVANS