MESOSCALE DISCUSSION 2224
   NWS STORM PREDICTION CENTER NORMAN OK
   0538 PM CDT SUN SEP 18 2005
   
   AREAS AFFECTED...SE SD...NE NEB...SW MN...NW IA
   
   CONCERNING...TORNADO WATCH 798...
   
   VALID 182238Z - 190015Z
   
   CONTINUE WW.  TRENDS ARE BEING MONITORED FOR INCREASING SEVERE
   THREAT AND POSSIBILITY OF WW ACROSS WESTERN/CENTRAL IOWA.
   
   ONGOING INTENSE CONVECTIVE DEVELOPMENT ACROSS THE MID MISSOURI
   VALLEY SEEMS TO BE IN RESPONSE TO FORCING ASSOCIATED WITH MID-LEVEL
   SHORT WAVE TROUGH EMBEDDED WITHIN BELT OF STRONGER FLOW EXTENDING
   OUT OF THE CENTRAL ROCKIES INTO THE NORTH CENTRAL PLAINS.  THIS
   FEATURE WILL GRADUALLY TURN EASTWARD...AROUND CREST OF SUBTROPICAL
   RIDGE...INTO THE MID MISSOURI VALLEY THIS EVENING.
   
   CONVECTIVE ACTIVITY PERHAPS OF MOST CONCERN NOW SEEMS TO BE EVOLVING
   IN CLUSTER NEAR O'NEILL NEB.  THIS IS OCCURRING WHERE LOW/MID-LEVEL
   WARM ADVECTION IS MAXIMIZED ON NORTHERN EDGE OF STRONG CAP...AND
   SHOULD GRADUALLY DEVELOP TOWARD THE SIOUX CITY IA AREA THROUGH
   00-01Z.  THERMODYNAMIC ENVIRONMENT SEEMS SUPPORTIVE OF RISK OF
   ISOLATED VERY LARGE HAIL IN STRONGEST CELLS...ALONG WITH DAMAGING
   DOWNBURSTS.
   
   STRONGER FORCING IS EXPECTED TO STRENGTHEN IN BAROCLINIC ZONE TO THE
   EAST SOUTHEAST OF ONGOING ACTIVITY...AND ADDITIONAL STRONG/SEVERE
   STORMS MAY DEVELOP EAST OF THE MISSOURI RIVER...INTO THE DES MOINES
   AREA...DURING THE EVENING.
   
   ..KERR.. 09/18/2005
   
   
   ATTN...WFO...DMX...FSD...OAX...GID...LBF...
   
   42759887 43139780 43409620 43249482 42739308 41399318
   40919495 41569584 41509722 41499826 42119899