MESOSCALE PRECIPITATION DISCUSSION 0558
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
728 AM EDT TUE JUL 25 2017

AREAS AFFECTED...WEST-CENTRAL TO SOUTHERN MS

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

VALID 251127Z - 251615Z

SUMMARY...AN AXIS OF SLOW-MOVING SHOWERS AND THUNDERSTORMS WITH
HEAVY RAIN IS EXPECTED TO EXPAND A BIT IN COVERAGE OVER THE NEXT
FEW HOURS. RAINFALL RATES TO 2 INCHES/HR COUPLED WITH THE SLOW
MOVEMENT WILL FOSTER SOME FLASH FLOODING CONCERNS.

DISCUSSION...EARLY MORNING EXPERIMENTAL GOES-16 10.3 MICRON/IR
DATA SHOWS A SMALL CLUSTER OF SLOWLY COOLING CONVECTIVE TOPS OVER
PARTS OF WEST-CENTRAL AND SOUTHWEST MS. THE CONVECTION IS FOCUSING
ALONG A WEAK LOW LEVEL CONFLUENCE AXIS AND IS BEING AIDED BY SOME
WEAK RIGHT-ENTRANCE REGION JET DYNAMICS ALOFT AHEAD OF AN UPPER
TROUGH JUST TO THE NORTHWEST OVER THE LOWER MS VALLEY. THE
ENVIRONMENT THAT THE CONVECTION IS FOCUSING IN IS VERY
MOIST...WITH PWATS OF 2 TO 2.25 INCHES. THE 09Z CIRA-LPW PRODUCT
SHOWS QUITE THE CONCENTRATION OF MOISTURE IN THE 500/300 MB
LAYER...WHICH WILL PROVIDE HIGHLY EFFICIENT RAINFALL PROCESSES.
THIS COUPLED WITH THE COOLING CONVECTIVE TOPS SUGGESTS THAT
RAINFALL RATES ARE INCREASING AT THIS TIME...AND WILL BE CAPABLE
OF EXCEEDING 2 INCHES/HR.

THE CONVECTION IS EXPECTED TO TEND TO SLOWLY BUILD EAST-SOUTHEAST
IN ALIGNMENT WITH THE BEST LOW LEVEL CONFLUENCE WHICH THE LATEST
RAP GUIDANCE SUGGESTS WILL TEND TO PERHAPS DRIFT SOUTHWARD THROUGH
THE MORNING HOURS.

THE LATEST HRRR GUIDANCE SUGGESTS THE POTENTIAL FOR SOME LOCALLY
VERY HEAVY RAINFALL GIVEN THE ANTICIPATED SLOW CELL MOTION AND
INTENSE RAINFALL RATES. IT SUPPORTS AS MUCH AS 3 TO 5 INCHES OF
RAIN THROUGH MIDDAY...WITH LOCALLY HEAVIER AMOUNTS TO OVER 6
INCHES. THE 00Z NSSL-WRF ALSO SUPPORTS SOME VERY HEAVY AND SIMILAR
TOTALS...BUT IT LIKELY HAS ITS QPF DEPICTED TOO FAR NORTH. THE
LATEST HRRR TENDS TO HAVE THE BETTER HANDLE ON THE ACTIVITY AT
THIS TIME.

SOME FLASH FLOODING CONCERNS WILL EXIST AS A RESULT WITH THESE
RAINFALL TOTALS AND THE SITUATION WILL BE CLOSELY MONITORED.

ORRISON

ATTN...WFO...JAN...LIX...MOB...

ATTN...RFC...LMRFC...

LAT...LON   32629071 32558995 32408948 32028895 31468846
            30998847 30708886 30738938 30839006 31059087
            31389135 31859134 32369113