MESOSCALE PRECIPITATION DISCUSSION 0860
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1058 AM EDT WED OCT 04 2017

AREAS AFFECTED...CENTRAL/NORTHERN OK

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

VALID 041455Z - 042055Z

SUMMARY...CLUSTERS OF HEAVY SHOWERS AND THUNDERSTORMS WITH VERY
HEAVY RAINFALL ARE EXPECTED OVER THE NEXT SEVERAL HOURS. SOME
FLASH FLOODING IS POSSIBLE.

DISCUSSION...NON-OPERATIONAL GOES-16 10.3 MICRON/IR IMAGERY IS
SHOWING A GRADUAL EXPANSION AND COOLING OF CONVECTIVE TOPS OVER
CENTRAL AND NORTHERN OK TO THE SOUTHEAST OF A FRONTAL ZONE AND OUT
AHEAD OF A WEAK SHORTWAVE IMPULSE APPROACHING THE REGION FROM THE
OK/TX PANHANDLES. THE CONVECTION IS ORGANIZING IN A VERY MOIST
ENVIRONMENT...WITH THE LATEST GPS-DERIVED PWATS RANGING FROM 2 TO
2.2 INCHES WHICH IS A SOLID 3+ SIGMAS ABOVE NORMAL FOR THIS TIME
OF THE YEAR.

THE CONVECTION IS EMBEDDED WITHIN ONLY A MODEST INSTABILITY
ENVIRONMENT THOUGH WITH MLCAPE VALUES OF 500 TO 1000
J/KG...HOWEVER THERE IS A FAIR DEGREE OF UPPER LEVEL DIVERGENCE
SEEN IN THE LATEST IR/WV IMAGERY WITH THE APPROACH OF THE UPSTREAM
SHORTWAVE...AND THUS THERE IS SOME LARGER SCALE ASCENT HELPING TO
COMPENSATE FOR THE GENERAL LACK OF INSTABILITY.
ADDITIONALLY...THERE IS EVIDENCE OF A WEAK SURFACE TROUGH OVER
CENTRAL OK WHICH IS PROVIDING FOR SOME LOCALLY FOCUSED AREAS OF
SURFACE CONVERGENCE. THIS IS ALSO AT LEAST LOCALLY HELPING TO
ENHANCE SOME OF THE CURRENT CONVECTIVE CLUSTERING SEEN IN RADAR
IMAGERY.

THE LATEST HRRR GUIDANCE WHICH HAD TENDED TO BE GENERALLY TOO WET
EARLY IN THE MORNING APPEARS TO GRADUALLY BE COMING INTO BETTER
ALIGNMENT WITH OBSERVATIONAL DATA AND APPEARS MORE
REASONABLE...ALBEIT PERHAPS STILL A TAD TOO WET LOCALLY. THE VERY
HIGH PWAT ENVIRONMENT AND COOLING OF CONVECTIVE TOPS WILL SUPPORT
VERY HIGH RAINFALL RATES THAT MAY EXCEED 2.5 INCHES/HR. THE LATEST
HRRR THROUGH 21Z FAVORS AS MUCH AS AN ADDITIONAL 3 TO 6
INCHES...WITH THE HEAVIEST TOTALS OVER CENTRAL OK. THESE TOTALS
MAY RESULT IN SOME FLASH FLOODING.

ORRISON

ATTN...WFO...OUN...TSA...

ATTN...RFC...ABRFC...

LAT...LON   36929723 36929616 36419571 35879606 35279773
            35089880 35449911 35999885 36479818