MESOSCALE PRECIPITATION DISCUSSION 0059
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
750 PM EST SAT MAR 10 2018

AREAS AFFECTED...AR...NRN MS

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

VALID 110048Z - 110548Z

SUMMARY...THUNDERSTORMS DUMPING UP TO 1.5-INCH PER HOUR RATES WILL
MOVE THROUGH AREAS STILL DEALING WITH LINGERING RIVER FLOODING AND
SOIL SATURATION. FLASH FLOODING IS POSSIBLE THIS EVENING/OVERNIGHT.

DISCUSSION...AS OF 0030Z SCATTERED THUNDERSTORMS WERE ONGOING OVER
MISSISSIPPI IN AN ENVIRONMENT MARKED BY WARM ADVECTION AND STEEP
LAPSE RATES PER THE 00Z KJAN AND KLZK SOUNDINGS. A SMALL MCS WAS
ATTEMPTING TO FORM IN WESTERN/CENTRAL ARKANSAS. GOES-16 WATER
VAPOR IMAGERY DEPICTED AN IMPRESSIVE SWIRL /SHORTWAVE TROUGH
DROPPING THROUGH NEBRASKA...AND MODELS DEPICT INCREASINGLY DEEP
FRONTOGENESIS AHEAD OF THIS FEATURE OVER NORTHERN ARKANSAS THROUGH
06Z IN THE VICINITY OF A QUASI-STATIONARY SURFACE FRONT. THIS
FORCING ALONG WITH INCREASED LOWER LEVEL INFLOW / 850 MB WINDS
RAMPING UP TO NEAR 30 KNOTS INTO SOUTHERN ARKANSAS / IN RESPONSE
TO THE UPSTREAM SHORTWAVE AND ASSOCIATED HEIGHT FALLS... SHOULD
LEAD TO INCREASED THUNDERSTORM COVERAGE / IF NOT ALSO ORGANIZATION
/ THIS EVENING.

ALTHOUGH HI-RES MODELS SHOWED SOMEWHAT VARIABLE TIMING OF
INITIATION... THEY GENERALLY AGREE TO THE NW TO SE ORIENTED SWATH
THROUGH WHICH A SMALL MCS MAY TRACK OVERNIGHT. WHILE THE ACTIVITY
APPROACHING LITTLE ROCK MAY BE THE MOST CONCENTRATED
INITIALLY...COVERAGE MAY INCREASE IN A SEPARATE AREA OVER
SOUTHEAST ARKANSAS WHERE SEVERAL CONSECUTIVE RAP RUNS PLACE DEEP
MASS FLUX CONVERGENCE...PARTICULARLY PEAKING AROUND 04Z. THE 12Z
WRF-ARW...HREF PROBABILITY MATCHED MEAN...AND 21Z HRRR ALL
APPEARED TO HAVE A GOOD HANDLE ON THINGS...AND WOULD SUPPORT THE
NOTION OF RAIN RATES PEAKING LOCALLY AT 1.5 INCHES PER HOUR
DESPITE THE INVOLVEMENT OF LARGE HAIL AND SOMEWHAT MARGINAL PW
VALUES.

FLASH FLOOD GUIDANCE TENDS TO RECOVER TOO QUICKLY POST-LARGE SCALE
FLOOD EVENTS...AND MAY NOT BE IDEALLY REPRESENTING THE FLASH FLOOD
RISK. THE MPD GRAPHIC OUTLINES AN AREA WHERE THE NATIONAL WATER
MODEL AND HRRR SOIL PRODUCTS INDICATE GREATER THAN 70 PERCENT SOIL
SATURATION LINGERING FROM RECENT FLOODING...WHICH COULD INCREASE
THE PERCENT OF SURFACE RUNOFF ASSOCIATED WITH THE RAINFALL
TONIGHT...LEADING TO A HEIGHTENED CHANCE OF SOME FLASH FLOODING.

BURKE

ATTN...WFO...JAN...LZK...MEG...

ATTN...RFC...ABRFC...LMRFC...SERFC...

LAT...LON   35699233 35229117 34509020 34118908 33278903
            32789014 33409195 34499335 35519356