Mesoscale Precipitation Discussion 0013
NWS Weather Prediction Center College Park MD
1124 PM EST Fri Jan 12 2024

Areas affected...Portions of the Northern Mid-Atlantic...Southeast
NY/Long Island...Southern New England

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

Valid 130423Z - 131023Z

SUMMARY...Heavy rains overspreading the northern Mid-Atlantic,
southeast NY/Long Island, and southern New England will be capable
of causing areas of flooding given the very wet antecedent
conditions including some areas of melting snow.

DISCUSSION...A deep layer cyclone lifting from the OH Valley into
the Great Lakes region will allow for a very strong northward
surge of warm air and moisture up along the Eastern Seaboard
overnight which will bring areas of heavy rainfall across coastal
and interior areas of the northern Mid-Atlantic into southern New
England.

Already there is an impressive southerly low-level jet on the
order of 60 to 70 kts nosing up across the Chesapeake Bay region
northward through eastern PA/NJ and aiming for southeast NY and
southern New England. Enhanced isentropic ascent associated with
this coupled with very strong levels of moisture transport through
the vertical column and a modest nose of elevated instability will
favor a general increase in rainfall rates going through the
overnight hours.

IVT magnitudes are forecast to increase to as much as 1000 to 1250
kg/m/s in the 06Z to 09Z time frame across many of these areas,
and especially toward northern NJ, southeast NY/Long Island and
southern New England. The 00Z HREF guidance supports high
probabilities (50% to 80%) of seeing rainfall rates increasing
into the 0.50" to 0.75"/hour range along the I-95 corridor
including the major metropolitan areas of Philadelphia and New
York City.

Some rainfall totals may reach as high as 1.5 to 2.5 inches by
dawn where some of these heavier rainfall rates set up and locally
train over the same area. Given the very wet antecedent conditions
that are in place from recent heavy rainfall, and also areas of
melting snow (especially the higher terrain of the Poconos,
Catskills, and Berkshires), these rains may result in areas of
flooding, and there will be some low-end urban flash flooding
potential if some of these rates can approach or even very briefly
exceed 1 inch/hour over the more sensitive metropolitan areas.

Orrison

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

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

LAT...LON   42687280 42557186 42167127 41777128 41297149
            40897212 40307337 39627404 37907525 38107643
            39117683 40337690 41647634 42357515 42667410