MESOSCALE PRECIPITATION DISCUSSION 0533
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
732 AM EDT SAT JUL 22 2017

AREAS AFFECTED...NORTHEAST MO & WEST-CENTRAL IL

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 221131Z - 221501Z

SUMMARY...THUNDERSTORMS ARE DROPPING SOUTHWARD INTO WEST-CENTRAL
IL AND NORTHEAST MO.  WITH PLENTY OF INSTABILITY, LOW-LEVEL
INFLOW, AND BULK SHEAR AVAILABLE, HOURLY RAIN RATES TO 1.5" WITH
LOCAL AMOUNTS TO 3" APPEAR POSSIBLE.

DISCUSSION...SATELLITE AND RADAR IMAGERY REVEAL AN MCV MOVING
THROUGH EASTERN IA AND AN UPSTREAM SHORTWAVE IS STILL APPARENT
NEAR THE BORDER OF THE DAKOTAS AND MN.  PRECIPITABLE WATER VALUES
OF 1.75-2" EXIST IN THIS REGION.  MU CAPE VALUES OF 1000-2000 J/KG
RESIDE UPSTREAM ACROSS MO, AND ARE BEING ADVECTED OVER THE OUTFLOW
BOUNDARY/EFFECTIVE FRONT INTO THE REGION BY WESTERLY 850 HPA
INFLOW OF 30-40 KTS, EXCEEDING THE MEAN 850-400 HPA WIND BY ~10
KTS.  EFFECTIVE BULK SHEAR OF ~30 KTS EXISTS, WHICH WHEN COMBINED
WITH NEARLY UNIDIRECTIONAL FLOW WITH HEIGHT IS TRYING TO ORGANIZE
THUNDERSTORMS INTO AN EAST-WEST BAND.

THE 00Z WRF NSSL HAD THE BEST GRASP OF THIS ACTIVITY, THOUGH ITS
CELL COVERAGE WAS MORE SPARSE THAN SEEN ON RECENT RADAR IMAGERY.
THE CONVECTIVE PATTERN HAS BEEN DROPPING SOUTH AT ROUGHLY 20 KTS
DURING THE LAST SEVERAL HOURS, PARALLEL TO THE 1000-500 HPA
THICKNESS PATTERN AND SLIGHTLY QUICKER THAN FORWARD PROPAGATING
CONVECTIVE VECTORS WOULD SUGGEST.  PATTERN-WISE, ONE WOULD
NORMALLY EXPECT THIS THUNDERSTORM ACTIVITY TO WANE AS THE MCV
MOVES EASTWARD INTO IL -- CLOUD TOPS HAVE BEEN WARMING WITHIN IR
SATELLITE IMAGERY, THOUGH THERE HAS BEEN RECENT COOLING NEAR
ALEXIS IL.  WITH AN UPSTREAM SHORTWAVE STILL APPARENT, AND 850 HPA
INFLOW NOT EXPECTED TO FALL UNDER 25 KTS UNTIL 17Z, THIS
CONVECTION COULD LINGER LONGER THAN THE NSSL WRF SUGGESTS.  HOURLY
RAIN RATES TO 1.5" AND LOCAL AMOUNTS TO 3" ARE ANTICIPATED, WHICH
COULD CHALLENGE LOCAL FLASH FLOOD GUIDANCE VALUES.

ROTH

ATTN...WFO...DMX...DVN...EAX...ILX...LSX...

ATTN...RFC...MBRFC...NCRFC...

LAT...LON   40818973 39898920 39078950 38529031 38769155
            39389249 40479318 40719137