MESOSCALE PRECIPITATION DISCUSSION 0020
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
847 PM EST TUE FEB 20 2018

AREAS AFFECTED...ARKANSAS

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

VALID 210145Z - 210745Z

SUMMARY...POTENTIAL FOR TRAINING HEAVY RAIN BANDS AND
THUNDERSTORMS WILL INCREASE INTO THE OVERNIGHT HOURS...WITH HOURLY
RAIN RATES LIKELY TO REACH OR EXCEED 1 IN/HR IN LOCALIZED NARROW
BANDS. THIS MAY LEAD TO SOME FLASH FLOODING IN AREAS WHERE HEAVY
RAIN CAN PERSIST FOR SEVERAL HOURS.

DISCUSSION...A DEEP FETCH OF MOISTURE EXTENDED INTO THE ARKLATEX
REGION ALONG A SLOWLY ADVANCING COLD FRONT...WITH PRECIPITABLE
WATER VALUES NEAR THE UPPER ECHELONS OF WHAT HAS BEEN OBSERVED AT
SOUNDING SITES IN THE MONTH OF FEBRUARY. IN FACT...THE 00Z
SOUNDING FROM SHREVEPORT LA RECORDED 1.72 INCH PW...WHICH BROKE
THE FEBRUARY RECORD (1.69 IN). CIRA LAYER PW PRODUCTS REVEAL A
PLUME OF SUBSTANTIAL MOISTURE THAT EXTENDS INTO THE MID-UPPER
LEVELS (BOTH THE 700-500MB AND 500-300MB LAYERS)...AND THIS DEEP
MOISTURE PLUME ORIGINATED AS FAR SOUTH AS 10N IN THE TROPICAL
EASTERN PACIFIC. THE DEEP MOISTURE PROFILE AND RECORD PWATS SHOULD
FAVOR EFFICIENT RAINFALL PRODUCTION IN CONVECTIVE BANDS THIS
EVENING AND INTO THE OVERNIGHT HOURS. SOME MESONET OBSERVATIONS
ACROSS THE REGIONS SUGGESTED THAT RADAR DUAL POL ESTIMATES WERE
REASONABLY CLOSE...BUT MAY BE UNDERESTIMATING SLIGHTLY...AND RATES
HAVE BEEN AS HIGH AS 1.5 IN/HR IN SOME CASES.

REGIONAL RADARS SHOWED A CONVECTIVE BAND AS OF 0130Z THAT EXTENDED
FROM NEAR MARSHALL AR TO NEAR ARKADELPHIA AR...AND THIS CONVECTIVE
BAND APPEARED TO BE SITUATED SLIGHTLY OFF THE SYNOPTIC FRONT.
WINDS WITH AN EASTERLY COMPONENT AND DEWPOINTS WELL INTO THE 60S
STILL EXISTED BEHIND THE CONVECTIVE BAND...PARTICULARLY PORTIONS
SOUTH OF I-40. GIVEN THE EXISTENCE OF FAIRLY STRONG FORCING BEHIND
THE ONGOING CONVECTIVE LINE...AND A SOUTHWESTERLY LOW-LEVEL JET
FEEDING INTO THE BACK OF THE LINE...POTENTIAL DOES EXIST FOR
FURTHER DEVELOPMENT AND BACKBUILDING DURING THE OVERNIGHT HOURS.
FLASH FLOOD POTENTIAL WOULD BE SLIGHTLY HIGHER IF BACKBUILDING
WERE TO OCCUR...BUT LOCALIZED FLASH FLOODING WILL STILL BE
POSSIBLE BASED ON THE ENVIRONMENT AND THE ONGOING
CONVECTION...WHICH IS EXHIBITING SOME TRAINING CHARACTERISTICS.

LAMERS

ATTN...WFO...LZK...MEG...PAH...SGF...SHV...

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

LAT...LON   37069135 37019033 36748986 36138989 35329040
            34619113 33859197 33279292 33119353 33249423
            33689431 34829379 35969309 36639235