Mesoscale Precipitation Discussion 1007
NWS Weather Prediction Center College Park MD
409 AM EDT Sat Nov 03 2018

Areas affected...Southern New England

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

Valid 030808Z - 031408Z

Summary...Moderate to locally heavy rainfall along and ahead of a
cold front will pose a flash flood risk across portions of
southern New England through the early morning hours.

Discussion...Strong negatively titled upper level shortwave trough
pushing through the lower Ohio Valley is contributing to broad
upper level divergence across the region. A plume of tropical
moisture characterized by PWATs of 1.4 to 1.7" has been advected
northward into portions of southern New England. At the surface, a
couple of lows were analyzed while a quasi-stationary boundary
lies from just offshore Maine through the urban corridor from
Portland, ME to Boston to NYC.

The line of showers is slowly advancing eastward while individual
cells are lifting north/northeast. With the unidirectional flow in
the low/mid levels, training will be possible. A recent
mesoanalysis shows MUCAPE up to 500 J/kg remains in place. Strong
boundary layer convergence is expected to remain in place,
contributing to a narrow corridor of moderate to heavy rain from
coastal southern Maine, New Hampshire down into portions of
MA/CT/RI.

Hourly rainfall rates of 1" will be possible into the morning
hours where convection taps into the remaining instability and
trains as it moves east/northeast. Total rainfall amounts of 1 to
locally 3 inches will be possible across portions of the area,
which might be enough to exceed the 3-hr FFG of 2-4". Urban
corridors and other sensitive areas will be most prone in this
setup. The progressive movement of the line combined with limited
instability and higher than normal FFG limits flash flood
confidence. However, given the potential for training convection
over urban/sensitive areas, longer duration nuisance flooding will
be possible.

Taylor

ATTN...WFO...ALY...BOX...GYX...OKX...

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

LAT...LON   44296929 42727086 41687022 41247338 42787249
            43787163