MESOSCALE PRECIPITATION DISCUSSION 0914
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
903 PM EDT WED OCT 25 2017

AREAS AFFECTED...DOWNEAST ME & VICINITY

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

VALID 260103Z - 260703Z

SUMMARY...SHOWERS AND BECOMING MORE PERSISTENT IN A
QUASI-STATIONARY BAND ACROSS DOWNEAST ME.  HOURLY RAIN TOTALS TO
~0.8" WITH LOCAL AMOUNTS TO 3" ARE POSSIBLE WHICH COULD LEAD TO
ISSUES IN AREAS OF POOR DRAINAGE.

DISCUSSION...AN AREA OF COOLING CLOUD TOPS HAS BEEN SEEN AS OF
LATE ON GOES-13 INFRARED IMAGERY WITHIN AN ATMOSPHERIC RIVER/AREA
OF SIGNIFICANT INTEGRATED VAPOR TRANSPORT WHICH CONTAINS A
STANDARDIZED ANOMALY OF 2-3 SIGMAS ABOVE AVERAGE FOR LATE OCTOBER.
THIS MOISTURE IS BEING DIRECTED FROM A TROPICAL DISTURBANCE ACROSS
CENTRAL AMERICA UP INTO NEW ENGLAND EAST OF A SHARP UPPER TROUGH
AND AHEAD OF THE POLAR FRONT.  THE EASTERN OF THE THREE FOCI OF
SHOWERS WHICH HAS BEEN THE MOST PRODUCTIVE IS WITHIN THE PLUME OF
DEEPEST MOISTURE, WITH PRECIPITABLE WATER VALUES ~1.75" PER GPS
DATA.  SHOWERS HAVE BECOME MORE PERSISTENT HERE OVER THE PAST
COUPLE HOURS, WITH RADAR ESTIMATES OCCASIONALLY REACHING 0.50" AN
HOUR.  INFLOW AT 850 HPA IS 35 KTS OUT OF THE SOUTH-SOUTHWEST. 
EFFECTIVE BULK SHEAR IS ~25 KTS.  MU CAPE VALUES ARE ROUGHLY 200
J/KG PER SPC MESOANALYSES.

A PORTION OF THE UPPER TROUGH NEAR THE SOUTHEAST COAST IS TAKING
ON A NEGATIVE TILT WHICH COULD LEAD TO SOME BACKING/ WESTWARD
DRIFT OF THE OVERALL PLUME ACROSS ME IN THE NEXT SEVERAL HOURS. 
THE ECMWF GUIDANCE SHOWS SOME INCREASE TO THE MU CAPE VALUES IN
THIS AREA OVER THE NEXT SEVERAL HOURS BY ~100 J/KG.  THE EXPECTED
GROWTH OF INSTABILITY COMBINED WITH THE AVAILABLE MOISTURE AND
SATURATED ATMOSPHERE COULD SUPPORT HOURLY RAIN TOTALS OF ~0.8" BY
06Z.  THE GUIDANCE SHOWS AN INCREASING TREND IN PRECIPITATION
AMOUNTS OVER THIS TIME, ADVERTISING LOCAL AMOUNTS IN THE 2-3"
RANGE BY 07Z.  CONSIDERING RECENT RAINFALL OF ~1" AND FALLING
LEAVES ACROSS THE NORTHEAST POTENTIALLY CLOGGING DRAINAGE IN THE
REGION, HEAVY RAIN RELATED ISSUES ARE EXPECTED TO INCREASE OVER
THE NEXT SIX HOURS.

ROTH

ATTN...WFO...CAR...GYX...

ATTN...RFC...NERFC...

LAT...LON   46756781 45796770 45646740 45296736 45256705
            44696703 44256825 43916947 45566873