MESOSCALE PRECIPITATION DISCUSSION 0927
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
507 PM EST SUN NOV 05 2017

AREAS AFFECTED...NE OHIO...NW PENNSYLVANIA...WRN NEW YORK

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

VALID 052137Z - 060237Z

SUMMARY...MODERATE RAIN WITH AN EMBEDDED BAND OF CONVECTION (WITH
HEAVIER RAIN) IS LIKELY TO GRADUALLY SHIFT FROM NRN OHIO AND LAKE
ERIE...TO NERN OHIO...NWRN PENNSYLVANIA...AND WRN NEW YORK LATE
THIS AFTERNOON AND THIS EVENING. RAIN RATES UP TO 1 IN/HR HAVE
BEEN ESTIMATED BY RADAR JUST OFFSHORE AND THIS MAY SHIFT OVER LAND
IN THE NEXT SEVERAL HOURS.

DISCUSSION...A LARGE AREA OF RAIN WITH AN EMBEDDED CONVECTIVE LINE
STRETCHED FROM SWRN ONTARIO AND LAKE ERIE BACK TO NEAR ST. LOUIS.
THE NORTHERN EXTENT OF THIS AREA OF RAIN WAS MUCH BROADER...AND
MODELS DO SHOW THE MODERATE TO OCCASIONALLY HEAVY RAIN PIVOTING
INTO PORTIONS OF THE ALLEGHENY PLATEAU BETWEEN 23Z AND 03Z. THE
SYNOPTIC SETUP FOR FLASH FLOODING IS GENERALLY MORE FAVORABLE TO
THE SOUTHWEST WITH THE STRONGEST LOW-LEVEL MOISTURE TRANSPORT AND
STRONGER INSTABILITY. HOWEVER...THE PLUME OF HIGHER PRECIPITABLE
WATER VALUES DOES EXTEND AS FAR NORTHEAST AS LAKE ERIE...WITH SOME
GPS-PW OBSERVATIONS AROUND 1.3 INCHES IN NW PA AND WRN NY. THIS IS
NEAR THE CLIMATOLOGICAL MAXIMUM FOR THIS TIME OF YEAR IN THIS
REGION. AND ALTHOUGH STRONGER LOW-LEVEL MOISTURE TRANSPORT EXISTS
FURTHER SOUTHWEST...THE LOW-LEVEL JET DOES EXTEND NORTHEAST INTO
NEW YORK AND SHOULD BE ABLE TO MAINTAIN MOISTURE FLUX INTO THE
REGION. THE INSTABILITY LEVELS ARE MORE MARGINAL...WITH MUCAPE
AROUND 200-500 J/KG. TAKEN IN SUM...THIS LIKELY MEANS A LESS
ORGANIZED AREA OF MODERATE TO OCCASIONALLY HEAVY RAINFALL CAN BE
EXPECTED.

ALTHOUGH THAT MAY LIMIT ORGANIZED CONVECTIVE BANDING TO A CERTAIN
EXTENT...TRAINING OF HEAVIER AREAS OF RAIN OR SMALL THUNDERSTORM
CLUSTERS CANNOT BE RULED OUT AS THE HIGHER REFLECTIVITY BAND (AS
OF 22Z) IS STILL FAVORABLY ALIGNED PARALLEL TO THE MEAN FLOW.
3-HOUR FLASH FLOOD GUIDANCE ACROSS ALMOST THE ENTIRE OUTLINED MPD
AREA IS AROUND OR BELOW 2 INCHES...AND THE NATIONAL WATER MODEL
ANALYSIS INDICATES NEAR-SURFACE SOIL AROUND 70-80 PERCENT OF
SATURATION. THEREFORE...ALTHOUGH RAIN RATES MAY NOT BE
PROLIFIC...THEY COULD BE HIGH ENOUGH TO CREATE FLOODING ISSUES
AROUND THE SOUTHERN RIM OF LAKE ERIE. AS MORE ORGANIZED CONVECTION
CURRENTLY OVER NORTH-CENTRAL OHIO CONTINUES TO PROGRESS EAST...IT
MAY PROVIDE A SECONDARY CORRIDOR OF HEAVIER RAINFALL FURTHER
INLAND.

LAMERS

ATTN...WFO...BUF...CLE...CTP...PBZ...

ATTN...RFC...MARFC...NERFC...OHRFC...

LAT...LON   42847887 42647815 42237794 41597832 41077908
            40737985 40488075 40608126 41298146 41728144
            42108073 42337980 42637920