Mesoscale Precipitation Discussion 0662
NWS Weather Prediction Center College Park MD
1001 PM EDT Tue Aug 14 2018

Areas affected...eastern NY/PA border into northwest NJ

Concerning...Heavy rainfall...Flash flooding possible

Valid 150200Z - 150630Z

SUMMARY...A flash flood threat will linger for another few hours
across portions of the eastern NY/PA border into northeastern PA
and northwestern NJ. Localized rainfall rates peaking in the 1 to
1.5 in/hr range can be expected with an additional 2-3 inches
expected by 06-07Z, before diminishing.

DISCUSSION...KBGM radar imagery over the past 1-2 hours showed
rainfall rates of 1-2 in/hr over Broome and Susquehanna counties
confirmed by surface observations, slowly translating
south-southeast. CIRA Layered PW imagery showed that the lingering
area of heavy rainfall rates was occurring within a region of deep
moisture just west of a mid-level low centered over eastern NY at
01Z, connected to a larger plume of moisture advancing through New
Brunswick by a narrow ribbon of moisture in the 700-500 mb layer.
SPC mesoanalysis data from 01Z showed MLCAPE along the eastern
NY/PA border was 500-1000 J/kg, coincident with the ongoing heavy
rain.

Training elements of heavy rain remain likely given that average
storm motions off toward the southeast are exceeded by a pocket of
stronger 850-700 mb northwesterly flow near 30 kt via area VAD
wind plots. Short term RAP forecasts show the mid-level low
advancing into central New England between 06-09Z with the ribbon
of higher low-mid level moisture to the west of the low center and
corridor of stronger 850-700 mb flow gradually lowering while
translating into northwest NJ through 06Z.

Given 3-hour Flash Flood Guidance is largely an inch or less along
the eastern NY/PA border into portions of eastern PA and northwest
NJ, flash flooding will remain possible with any local flare ups
of heavy rain, with the threat likely diminishing beyond about 06Z
as upper forcing becomes less favorable along with further
reductions to remaining CAPE.

Otto

ATTN...WFO...ALY...BGM...CTP...OKX...PHI...

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

LAT...LON   42767576 42677526 42507504 42087474 41747454
            41177412 40587438 40337492 40367550 40477603
            40737639 41197658 41837674 42337652 42637620