Mesoscale Precipitation Discussion 0684
NWS Weather Prediction Center College Park MD
510 PM EDT Fri Aug 17 2018

Areas affected...Portions of the Upper OH Valley...Northern
Mid-Atlantic...NY and New England

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

Valid 172110Z - 180310Z

Summary...Showers and thunderstorms continue to organize and
expand in coverage over the next several hours. Given the locally
very wet antecedent conditions, some flash flooding will be
possible.

Discussion...Multiple shortwave troughs are advancing up across
the lower Great Lakes and New England this afternoon which is
helping to gradually advance a cold front off to the southeast as
a wave of low pressure lifts up across far eastern Ontario. A warm
front meanwhile is lifting northeast up across the interior of the
Northeast.

The warm sector is characterized by a southwest flow regime which
is moderately unstable with as much as 2000 j/kg of MLCAPE, and it
is quite moist with PWATS of 1.7 to 1.9 inches. Robust diurnal
heating this afternoon in conjunction with modest deep layer
ascent associated with the shortwave energy traversing the lower
Great Lakes and New England has allowed numerous small scale
clusters of convection to develop and lift progressively off to
the northeast. Over the next few hours, there will tend to be some
additional convective organization as somewhat stronger shear
profiles arrive from the OH Valley and couple with the
aforementioned boundary layer instability. This will set the stage
for some linear convective bands that may tend to train over the
same area. Some cell-merger activity will be possible as well.

The latest hires model consensus favors some heavy rainfall totals
of as much as 3 to 4 inches locally going through 03Z. Portions of
the threat area are quite sensitive given heavy rainfall from
earlier in the week, and these areas include northern PA, southern
NY and adjacent areas of central and southern New England. Given
the expected rainfall amounts through this evening, some flash
flooding will be possible.

Orrison

ATTN...WFO...ALY...BGM...BOX...BTV...BUF...CLE...CTP...GYX...
LWX...OKX...PBZ...PHI...RLX...

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

LAT...LON   44857293 44277150 42797174 41817255 41027353
            40297496 39867727 39657855 39538068 39728198
            40318210 40928153 42137910 42747805 43597633
            44437472