MESOSCALE DISCUSSION 0399
   NWS STORM PREDICTION CENTER NORMAN OK
   0238 PM CDT SAT MAR 31 2007
   
   AREAS AFFECTED...ERN NEB...IA...PARTS OF NE MO...W CNTRL
   
   CONCERNING...TORNADO WATCH 100...101...
   
   VALID 311938Z - 312115Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCHES 100...101...
   CONTINUES.  TORNADO POTENTIAL SEEMS LIKELY TO INCREASE IN PEAK
   AFTERNOON HEATING NEXT FEW HOURS.
   
   LOW/MID-LEVEL CYCLONE CONTINUES TO DEEPEN ACROSS THE MID MISSOURI
   VALLEY...WITH SURFACE LOW CENTER NOW NEAR OMAHA NEB...WHERE RAPID
   2-HOUR PRESSURE FALLS PERSIST.  A SUBSTANTIAL INCREASE IN
   THUNDERSTORM ACTIVITY IS ONGOING IN BAND OF STRONGER DIFFERENTIAL
   CYCLONIC VORTICITY ADVECTION AHEAD OF UPPER IMPULSE...WHICH WILL
   GRADUALLY PIVOT THROUGH THE MID MISSOURI VALLEY LATE THIS AFTERNOON.
   
   
   ALTHOUGH LOW-LEVEL HODOGRAPHS IN CLOSE PROXIMITY TO SURFACE LOW
   CENTER ARE NOT PARTICULARLY LARGE...LOW-LEVEL LAPSE RATES HAVE
   STEEPENED WITH DAYTIME HEATING AND DIFFERENTIAL THERMAL
   ADVECTION...EASTWARD ALONG WARM FRONT INTO THE DES MOINES AREA. 
   AND...THOUGH LITTLE TORNADIC ACTIVITY HAS BEEN EVIDENT SINCE EARLY
   INITIAL REPORT OVER SOUTHEAST NEBRASKA...LARGE AMBIENT VERTICAL
   VORTICITY ALREADY PRESENT IN THE VICINITY OF THE BOUNDARY WILL
   SUPPORT CONTINUING POTENTIAL FOR AT LEAST BRIEF TORNADOES...IN
   ADDITION TO HAIL LATE THIS AFTERNOON.
   
   INCREASING POTENTIAL FOR TORNADOES BY 21-22Z MAY DEVELOP INTO AREAS
   WEST OF CEDAR RAPIDS IA...WHERE ARCING BAND OF STORMS IS EXPECTED TO
   INTERSECT WARM FRONT.  OBJECTIVE ANALYSIS INDICATES WARM ADVECTION
   HAS BECOME MAXIMIZED ACROSS THIS AREA...WITH DEVELOPING CENTER OF
   2-HOUR PRESSURE FALLS.  AND...LOW-LEVEL HODOGRAPHS REMAIN LARGE
   ACROSS THIS REGION...WITH POTENTIAL 0-1 KM STORM RELATIVE HELICITY
   ESTIMATED IN EXCESS OF 200 M2/S2.
   
   ..KERR.. 03/31/2007
   
   
   ATTN...WFO...DVN...DMX...FSD...OAX...
   
   41859664 42329615 42429478 42369327 41939227 41469215
   40889239 40719344 40749465 40909591 41139626