MESOSCALE PRECIPITATION DISCUSSION 0069
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
557 PM EDT SUN MAY 26 2013
 
AREAS AFFECTED...CENTRAL AND SOUTHERN IA...NORTHEAST
MISSOURI...WESTERN IL 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 262154Z - 270200Z
 
SUMMARY...PASSAGE OF A MID LEVEL TROUGH WILL COINCIDE WITH MAX
DIURNAL HEATING TO YIELD ADDITIONAL POCKETS OF HVY RAIN OVER
IA/IL...AND A SEPARATE AREA OF HVY RAIN/FLASH FLOODING OVER
NORTHEAST MO.

DISCUSSION...THE SYNOPTIC SCALE WAS RELATIVELY UNCHANGING.
MULTIPLE ROUNDS OF THUNDERSTORMS WITH MDT/HVY RAIN HAD OCCURRED
WITHIN A FRONTAL ZONE DOWNWIND OF A VERY UNSTABLE BUT CAPPED GREAT
PLAINS AIR MASS. FLASH FLOOD GUIDANCE HAD DROPPED
SEVERELY...PARTICULARLY IN A BROAD SWATH NW TO SE ACROSS IA AND
WESTERN IL.

BY 2130Z...RADAR TRENDS SUGGESTED INCREASING ORGANIZATION AND
INTENSITY OF THREE STORM CLUSTERS. ONE ROOTED ABOVE THE SURFACE IN
EASTERN IA NEAR IOWA CITY AND ONE SURFACE-BASED CLUSTER NEAR
COLUMBIA MISSOURI WHERE LOCATED AHEAD OF A 700MB SHORTWAVE TROUGH
THAT WILL PROVIDE ORGANIZED LIFT AND ENHANCED LOW LEVEL INFLOW
THROUGH THE EARLY EVENING. THE THIRD CLUSTER IN WESTERN IOWA WAS
RELATED TO COLD POOL FORCING HAVING ARRIVED FROM A COMPLEX THAT
DATES BACK TO LAST EVENING. MODELS PREDICT DIMINISHING LOW LEVEL
WINDS OVER WESTERN IOWA...BUT THE COLD POOL MAY ALLOW THE SYSTEM
TO PERSIST AT LEAST THROUGH 23-00Z PER 17Z HRR.

WITH ALL OF THESE SYSTEMS...CELLS WILL BRIEFLY TRAIN NORTHEASTWARD
WHILE THE CLUSTERS TRANSLATE EAST TO SOUTHEAST. THE IA ACTIVITY
SHOULD REMAIN PROGRESSIVE AND MAY IMPACT WESTERN IL... DELIVERING
AN ADDITIONAL 1-1.5 INCHES OF RAIN WHERE 1-3 HR FFG WAS AT A
MINIMUM. THE MISSOURI ACTIVITY COULD BECOME MORE TROUBLESOME OWING
TO GREATER INSTABILITY/PW VALUES 1.5-1.6 INCHES/ AND LOW LEVEL
WINDS THAT FAVOR SOME UPDRAFT ROTATION TO SLOW THE STORM MOTIONS.
BUNKERS RIGHT MOVER MOTION NOTED NEAR ZERO IN THIS AREA. IF THE
ACTIVITY GROWS UPSCALE...AS HINTED IN THE HEAVY QPF FROM THE
NAM/GFS...FLOODING WOULD BE MOST LIKELY ON THE WSW FLANK OF THE
RELATED COLD POOL...MOST LIKELY TO SET UP OVER CENTRAL/EAST
CENTRAL MO JUST WEST OF ST LOUIS.

BURKE


ATTN...WFO...ILX...LSX...DVN...SGF...DMX...EAX...FSD...OAX...

LAT...LON   42559240 42639365 42659508 42599581 42239594 41339540
            40869389 40189317 38809315 38379271 38169175 38559081
            39109032 40189016 41299042 41909103 42159150 42559240