MESOSCALE DISCUSSION 1827
   NWS STORM PREDICTION CENTER NORMAN OK
   1006 PM CDT MON AUG 20 2007
   
   AREAS AFFECTED...IOWA...NRN MO
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 626...
   
   VALID 210306Z - 210430Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 626
   CONTINUES.
   
   MID-LEVEL IMPULSE SUPPORTING ONGOING STORMS WILL CONTINUE EAST OF
   THE MIDDLE MISSOURI VALLEY THIS EVENING...WITHIN A WEAKER BELT OF
   WESTERLIES WHICH UNDERCUTS UPPER GREAT LAKES MID-LEVEL RIDGE...
   DOWNSTREAM OF POLAR TROUGH.  AT THIS POINT...IT APPEARS MUCH OF THE
   CONVECTIVE DEVELOPMENT IS NOT EMANATING FROM THE BOUNDARY
   LAYER...BUT RATHER BASED IN A LOWER/MID TROPOSPHERIC WARM ADVECTION
   REGIME...WHERE CAPE IS NOT NEARLY AS LARGE AS SUGGESTED BY LATEST
   RUC MOST UNSTABLE CAPE GUIDANCE.  AN EXCEPTION COULD BE SMALL
   CLUSTER NEAR LAMONI...DEVELOPING ON THE NOSE OF NEAR SURFACE THROUGH
   850 MB THERMAL RIDGE.  BUT...EVEN THIS ACTIVITY MAY BECOME
   INCREASINGLY ELEVATED WITH TIME AS IT CONTINUES EASTWARD IN THE
   VICINITY THE IOWA/MISSOURI BORDER.  DESPITE THE ELEVATED NATURE OF
   THE STORMS...SOUNDINGS SUGGEST CONTINUING POTENTIAL FOR STRONG
   EVAPORATIVE COOLING IN A LAYER ABOVE THE DECOUPLING BOUNDARY LAYER
   THROUGH 700 MB...SUPPORTING THE POSSIBILITY OF ADDITIONAL DOWNBURSTS
   THROUGH AT LEAST THE 05-06Z TIME FRAME.  GREATEST THREAT APPEARS TO
   EXIST FROM THE DES MOINES AREA... SOUTH/SOUTHEASTWARD INTO THE
   MISSOURI BORDER
   
   ..KERR.. 08/21/2007
   
   
   ATTN...WFO...LSX...DVN...DMX...EAX...FSD...
   
   43279579 43539506 42959333 42099240 40929152 40289195
   40279326 40549478 41739465