MESOSCALE PRECIPITATION DISCUSSION 0005
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
927 AM EST FRI JAN 12 2018

AREAS AFFECTED...NY...VT...NH...WRN MA...CT...NRN NJ

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

VALID 121426Z - 122015Z

SUMMARY...MODERATE TO OCCASIONALLY HEAVY RAIN IS EXPECTED TO
CONTINUE TO AFFECT THE NORTHEAST THROUGH THE DAY...AND IN
COMBINATION WITH SNOWMELT IS LIKELY TO LEAD TO AREAS OF FLOODING.
LOCALIZED FLASH FLOODING WILL BE POSSIBLE IN AREAS WHERE GREATER
RAIN RATES CAN PERSIST FOR SEVERAL HOURS.

DISCUSSION...A SIGNIFICANT PLUME OF LOW-MID LEVEL MOISTURE IS
SURGING NORTH ALONG THE EAST COAST PER CIRA LAYER PW AND BLENDED
TPW PRODUCTS. THE 700-500MB LAYER PW PRODUCT SHOWS A SIGNIFICANT
ENHANCEMENT FROM EASTERN NORTH CAROLINA TO SOUTHERN NEW JERSEY AND
CURRENT TRENDS SUGGEST THIS WILL CONTINUE TO BE ADVECTED TO THE
NNE INTO PORTIONS OF NEW ENGLAND ALONG THE MEAN MID-LEVEL FLOW
VECTORS THROUGH THE DAY. THE UNUSUALLY ROBUST AND DEEP MOISTURE
PLUME FOR MID-JANUARY IS SETTING SOME MONTHLY RECORDS...WITH BOTH
THE 12Z BUFFALO AND ALBANY SOUNDINGS SETTING JANUARY RECORDS FOR
PRECIPITABLE WATER VALUES. THE ANOMALOUS LOW-MID LEVEL MOISTURE
SHOULD BE MORE THAN SUFFICIENT FOR HEAVY RAINFALL IN AREAS WHERE
SUSTAINED FORCING CAN PRODUCE MORE FOCUSED BANDS OF RAIN.

ONE SUCH BAND DEVELOPED OVERNIGHT...ARCING FROM WEST VIRGINIA
NORTHEAST INTO PORTIONS OF WRN AND NRN NEW YORK STATE. A LACK OF
INSTABILITY MEANT THAT THIS WAS LARGELY STRATIFORM RAIN BUT
LOW-LEVEL THETAE ADVECTION AND MOISTURE CONVERGENCE HELPED FOCUS A
BAND OF MODERATE TO OCCASIONALLY HEAVY RAINFALL. WHAT REMAINS OF
THIS RAIN BAND SHOULD CONTINUE TO TRACK OVER PORTIONS OF W/N NEW
YORK THROUGH THE DAY...AND MAY BEGIN TO REDEVELOP LATER IN THE
AFTERNOON AS THE SURFACE COLD FRONT APPROACHES AND LOW-LEVEL
CONVERGENCE INCREASES.

FURTHER TO THE EAST...LOW-LEVEL MOISTURE TRANSPORT AND THE PLUME
OF HIGHEST PWATS SHOULD BECOME INCREASINGLY FOCUSED IN A CORRIDOR
FROM NEW JERSEY NNE INTO NEW HAMPSHIRE...AND HI-RES MODELS SHOW A
BAND OF MDT-HVY RAIN BECOMING MORE ORGANIZED INTO THE AFTERNOON
HOURS IN THIS SAME CORRIDOR. THE PROJECTED ORIENTATION OF THIS
RAIN BAND SHOULD LARGELY BE ALIGNED WITH LOW-MID LEVEL MEAN FLOW
WHICH MAY PRODUCE A BAND OF RAIN TOTALS AS HIGH AS 1-2 INCHES BY
21Z.

SUCH RAINFALL TOTALS PRODUCED NUMEROUS FLOODING REPORTS OVERNIGHT
IN THE VICINITY OF WRN PA AND WRN NY WHEN COMBINED WITH SOME
EXISTING SNOW AND COLD GROUND TEMPERATURES. THESE ARE ALSO THE
ANTECEDENT CONDITIONS ACROSS MOST OF THE HIGHLIGHTED AREA.
NEAR-SURFACE SOIL TEMPERATURES ARE NEAR OR BELOW FREEZING ACROSS
MUCH OF THE AREA WHICH MAY ENHANCE RUNOFF POTENTIAL.
THEREFORE...RELATIVELY MARGINAL RAIN RATES COULD PRODUCE RATES OF
RUNOFF MORE CONSISTENT WITH HIGHER RAIN RATES.
ADDITIONALLY...NOHRSC ANALYSIS SHOWS THERE ARE SIGNIFICANT AMOUNTS
OF LIQUID WATER IN THE SNOWPACK ACROSS THE REGION...WITH AMOUNTS
OVER 1 INCH IN THE TUG HILL AND ADIRONDACKS OF NEW YORK...AND THEN
THE ELEVATED TERRAIN IN VT...NH...AND WRN MA AS WELL AS MUCH OF
MAINE. ALTHOUGH SUCH SNOW MELT WOULD BE RELATIVELY GRADUAL...IT
WILL ALSO PRODUCE AN ADDED ENHANCEMENT TO RUNOFF FROM ANY RAINFALL
IN THE REGION. FOR THIS REASON...FLOODING SEEMS LIKELY ACROSS MUCH
OF THE NORTHEAST...AND MORE RAPID ONSET FLASH FLOODING WILL BE
POSSIBLE IN AREAS WHERE HEAVY RAIN RATES CAN PERSIST FOR SEVERAL
CONSECUTIVE HOURS.

LAMERS

ATTN...WFO...ALY...BGM...BOX...BTV...BUF...GYX...OKX...PHI...

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

LAT...LON   45207150 44987075 44277054 43217140 41787263
            40827333 40417412 40937484 41617476 42207452
            42767460 42917525 42717596 42467662 42107759
            42237837 42747846 43267767 43677667 44347649
            44837567 45137479 45147360 45127247