Flash Flood Guidance
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000
AWUS01 KWNH 231427
FFGMPD
MAZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-232026-

Mesoscale Precipitation Discussion 0110
NWS Weather Prediction Center College Park MD
1027 AM EDT Sat Mar 23 2024

Areas affected...portions of Maryland, , Washington DC, New
Jersey, eastern Pennsylvania, southern New York, and southwestern
New England

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

Valid 231426Z - 232026Z

Summary...A long-duration, moderate to heavy rain event is
unfolding generally along the urban corridor of I-95 from
Washington DC through New York City.  Areas of 0.25-0.5 inch/hr
rain rates should continue to spread northeastward with time,
causing issues with excessive runoff.

Discussion...Recent radar mosaic imagery/MRMS indicates widespread
areas of moderate to heavy rainfall, with the heaviest of rates
(0.25-0.7 inch/hr) focused along an axis from Washington DC and
Chesapeake Bay north through the Philadelphia Metro area.  These
rain rates are focused within an axis of low-level convergence on
the northwestern edge of a stout, south-southeasterly 850mb
low-level jet just east of the Mid-Atlantic.  A low-level cyclone
(centered over central Virginia) was also contributing to the
strength of the low-level jet, and should strengthen while
migrating north-northeastward toward eastern Pennsylvania over the
next 6 hours.  Heavier rain rates will continue to shift
north-northeastward in tandem with this low, eventually spreading
into more of Philadelphia, New Jersey, southern New York
(including New York City), and southwestern New England through
21-22Z.

As the rain rates continue (and modestly increase) through 21Z,
they will overspread sensitive, urbanized areas, encouraging
runoff.  Widespread areas of minor flood impacts are expected, and
isolated flash flooding is possible.  3-hour rainfall totals of
1-1.5 inches should approach or locally exceed FFGs across the
region (which happen to be highest in populated areas near the
I-95 corridor), again supporting localized flash flood potential.
Much of the heavier rainfall (and associated flash flood risk)
should wane across Maryland and Washington DC after around 17Z,
while ramping up across the northeastern half of the discussion
area (New Jersey into southern New York) in the 17-21Z timeframe.

Cook

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...AKQ...ALY...BGM...BOX...CTP...LWX...OKX...PHI...

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

LAT...LON   42127298 41627222 40697217 39417356 37807535
            37447607 38497701 38807707 39287733 39797703
            41167531 41947391


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