MESOSCALE PRECIPITATION DISCUSSION 0750
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
955 AM EDT FRI OCT 21 2016
 
AREAS AFFECTED...NORTHERN/CENTRAL PA...SOUTHERN NY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 211350Z - 211900Z
 
SUMMARY...HEAVY RAINFALL IS REDEVELOPING AND FALLING OVER AREAS
WITH NEARLY SATURATED SOIL. GIVEN THE HEAVY RAINFALL FROM
OVERNIGHT...ADDITIONAL RUNOFF AND/OR FLASH FLOODING IS POSSIBLE.

DISCUSSION...THE LATEST WV IMAGERY SHOWS AN UPPER TROUGH
CONTINUING TO DIG ACROSS THE OH VALLEY...WITH A RATHER STRONG AXIS
OF DIVERGENT FLOW ALOFT NOTED ACROSS THE NORTHERN MID-ATLANTIC
REGION IN ASSOCIATION WITH 250 MB RIGHT-ENTRANCE REGION JET
DYNAMICS. THE AMPLIFYING TROUGH ALOFT AND INTERACTION WITH A
STRONG FRONTAL ZONE IS FACILITATING A WAVE OF LOW PRESSURE ACROSS
SOUTHWEST PA. SURFACE OBSERVATIONS SHOW THIS NORTHWEST OF ALTOONA
PA...WITH A COLD FRONT EXTENDING SOUTH ACROSS SOUTHWEST PA AND THE
MD/WV PANHANDLES. MEANWHILE...A STATIONARY FRONT IS ORIENTED
NORTHEAST OF THE LOW CENTER ACROSS NORTH-CENTRAL PA AND INTO
SOUTHERN NY. THE WAVE OF LOW PRESSURE IS HELPING TO CONCENTRATE A
STEADY LOW LEVEL SOUTHERLY FETCH OF WARM/MOIST AIR UP ACROSS
CENTRAL PA...AND RADAR IMAGERY CONTINUES TO SHOW A LARGE AREA OF
MODERATE TO HEAVY RAINFALL FOCUSING ALONG AND TO THE NORTHWEST OF
THE FRONTAL BOUNDARY GIVEN ROBUST ISENTROPIC ASCENT AND LARGE
SCALE FORCING ASSOCIATED WITH THE UPPER JET DYNAMICS.

SURFACE DEW POINTS ARE AS HIGH AS THE LOW TO MID 60S AHEAD OF THE
LOW CENTER...AND LAYER PWATS 1.1 TO 1.2 INCHES WHICH IS ABOUT 1 TO
2 STANDARD DEVIATIONS ABOVE NORMAL. THIS IS CONTRIBUTING TO
RELATIVELY EFFICIENT RAINFALL PROCESSES THAT ARE CONTRIBUTING TO
HEAVIER RAINFALL RATES.

DESPITE EXTREMELY WEAK INSTABILITY...THERE HAS BEEN SOME UPTICK IN
RAINFALL RATES THE LAST COUPLE OF HOURS AS SOME EMBEDDED
CONVECTIVE ELEMENTS ARE SEEN FOCUSING NEAR AND NORTH OF THE
SURFACE LOW TRACK. OVER THE NEXT FEW HOURS...SOME ADDITIONAL HEAVY
RAINS WILL FOCUS OVER PORTIONS OF CENTRAL PA AND EXTENDING NORTH
INTO SOUTHERN NY. SOME AREAS JUST WEST AND NORTH OF STATE COLLEGE
RECEIVED 6 TO 8 INCHES OF RAIN OVERNIGHT...AND ANY ADDITIONAL
HEAVY RAINFALL WILL LIKELY AGGREVATE CONCERNS FOR ADDITIONAL
RUNOFF AND/OR FLASH FLOODING. ADJACENT AREAS OF NORTH-CENTRAL PA
AND SOUTHERN NY HAVE ALSO BEEN SEEING A GRADUAL SATURATING OF THE
SOIL SUCH THAT RUNOFF PROBLEMS WILL BECOME MORE PROBABLE.

ADDITIONAL RAINFALL OF 1 TO 2 INCHES WITH LOCALLY HEAVIER AMOUNTS
ARE POSSIBLE THROUGH EARLY AFTERNOON BEFORE CONDITIONS IMPROVE IN
THE WAKE OF THE LOW CENTER PASSAGE.

ORRISON

ATTN...WFO...BGM...BUF...CTP...PBZ...

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

LAT...LON   42777728 42727632 41947654 41187702 40797761 
            40547815 40657870 41067884 41997831