Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Aug 18 2023 01:35:49

AWUS01 KWNH 180135
FFGMPD
NYZ000-NJZ000-PAZ000-180734-

Mesoscale Precipitation Discussion 0940
NWS Weather Prediction Center College Park MD
934 PM EDT Thu Aug 17 2023

Areas affected...Central to Northeast PA...Southern and Central NY

Concerning...Heavy rainfall...Flash flooding likely

Valid 180134Z - 180734Z

SUMMARY...Heavy showers and thunderstorms will be developing and
expanding in coverage over the next several hours across areas of
central to northeast PA and into central and southern NY. Given
moist antecedent conditions, scattered instances of flash flooding
will be likely.

DISCUSSION...The latest GOES-E WV suite shows a strong upper-level
trough crossing the Great Lakes region and taking aim for the
Northeast for the overnight hours. This energy will gradually be
interacting with the southerly low-level return of moisture and
instability from the Mid-Atlantic states and will drive developing
and expanding coverage of heavy showers and thunderstorms over the
next several hours.

MLCAPE values of 500 to 1000 J/kg have nosed up into areas of
south-central to southeast PA over the last few hours with aid of
a moistening boundary layer, and the latest RAP guidance shows a
much stronger destabilization of the low-levels in the 03Z to 06Z
time frame across the eastern half of PA and into southern and
eastern NY as the low-level jet increases to 30 to 40+ kts.

This increasing moisture and instability transport will coincide
with the arrival of a 90 to 100 kt 250mb jet streak rounding the
base of the upper trough to drive what should end up being a
rather organized axis of convection with at least clusters of
convection that will also occasionally be capable of repeating
over the same area.

PWs are forecast to rise to 1.5 to 1.75 inches, and with the
instability, and localized orographics/upslope flow over some of
the ridges, the rainfall rates will be rather high and capable of
reaching as high as 2 inches per hour with the stronger cells.

The 18Z HREF guidance supports as much as 3 to 4 inches of rain
for the MPD valid time frame, and with antecedent conditions
across the area quite moist, these rains are likely to result in
scattered instances of flash flooding heading into the overnight
hours.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!8qX1mZn-n8OEnRIOpHSpxp_osJHiBJ_LcsZQaGF7gJcOxTigYzAozZGJwSw-VAMx-dCy=
uah3cZwfCjM2wW30KwkUAQQ$  for graphic product...

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

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

LAT...LON   44217469 43777386 42587398 41117474 40577544=20
            40367638 40777738 41657737 42567682 43387632=20
            44057570=20

=3D =3D =3D
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