Graphic for MPD #0174

MESOSCALE PRECIPITATION DISCUSSION 0174
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1211 PM EDT SUN APR 30 2017

AREAS AFFECTED...SOUTHEAST LA & SOUTHERNMOST MS

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

VALID 301610Z - 302050Z

SUMMARY...THUNDERSTORMS ARE STARTING TO SLOW THEIR EASTERN ADVANCE
ACROSS SOUTHEAST LA AS THEY RUN AHEAD OF THE MAIN SYNOPTIC
BOUNDARY.  HOURLY RAIN RATES TO 2.5", WITH LOCAL AMOUNTS OF 3-5",
COULD LEAD TO ISSUES.

DISCUSSION...THE 15-16Z SURFACE OBSERVATIONS INDICATED THAT THE
CONVECTIVE LINE MOVING ACROSS MS AND SOUTHEAST LA HAD OUTPACED THE
SURFACE FRONT WHICH HAS ITSELF STALLED NEAR THE ATCHAFALAYA/MS
RIVER, AND SOME SLOWING HAD BEEN NOTED TO CONVECTIVE PROGRESSION
ON RADAR IMAGERY.  THE 00Z ARW SHOWED THIS SORT OF SOLUTION
EARLIER.  PRECIPITABLE WATER VALUES OF ~2" LIE ACROSS THE AREA,
AND INFLOW AT 850 HPA IS CONVERGENT WITH SPEEDS OF 40-55 KTS PER
NEARBY VAD WIND PROFILES.  DEW POINTS IN THE MID 70'S LIE SOUTH OF
THE MESOSCALE WARM FRONT IN SOUTHERN MS AND SOUTHERN AL.  BULK
SHEAR IN THE 0-6 KM LAYER APPROACHES 40 KTS, WHICH HAS AT TIMES
LED TO CONVECTIVE WAVES WITHIN THE SQUALL LINE.

THE 14Z HRRR APPEARS TO HAVE THE BEST HANDLE ON THE SITUATION DOWN
THERE FROM A HEAVY RAIN PATTERN PERSPECTIVE.  WITH THIS SORT OF
DISTANCE BETWEEN THE TWO BOUNDARIES, THE RAINFALL PATTERN COULD
BROADEN SOMEWHAT WHICH ALONG WITH POSSIBLE WAVES IN THE CONVECTIVE
PATTERN WOULD HEIGHTEN THE RISK FOR HEAVIER RAINFALL.  HOURLY RAIN
RATES COULD RAMP UP TO 2.5", WITH LOCAL AMOUNTS OF 3-5" ARE
POSSIBLE OVER THE NEXT SEVERAL HOURS.  THIS AMOUNT OF RAIN WOULD
CHALLENGE THE HIGH FLASH FLOOD GUIDANCE VALUES.

ROTH

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

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

LAT...LON   31348938 31118850 30138831 29068893 28868921
            28928946 29218975 29049011 28969055 29059106
            29239132 29469146 29569150 30389104 31019045
           


Last Updated: 1211 PM EDT SUN APR 30 2017