922
AWUS01 KWNH 221651
FFGMPD
MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-NJZ000-PAZ000-222250-

Mesoscale Precipitation Discussion 0488
NWS Weather Prediction Center College Park MD
1250 PM EDT Sat Jun 22 2024

Areas affected...North-Central to Northeast PA...Northern
NJ...South-Central to Southeast NY...Long Island...Southern New
England

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

Valid 221650Z - 222250Z

SUMMARY...Showers and thunderstorms with locally very heavy
rainfall rates are expected this afternoon and into the early
evening hours. Isolated to scattered instances of flash flooding
will be possible, including some urban flash flooding concerns.

DISCUSSION...The latest surface analysis shows a quasi-stationary
front draped in a general west-northwest to east-southeast fashion
from central NY down through eastern CT/RI and far southeast MA.
Meanwhile, there is a weak wave of low pressure traversing the
front which coupled with some subtle mid-level vort energy aloft
appears to be driving the cluster of showers and thunderstorms
focused to the west and north of Albany, NY.

Strong boundary layer heating is already yielding a moderately
buoyant airmass across north-central PA through south-central NY
and stretching east into areas of western MA, with MLCAPE values
locally of 1000 to 2000 J/kg. A very moist environment is in place
with high PWs of 1.8 to 2.0 inches. The 12Z RAOBs from ALB and OKX
this morning depicted 1.94 and 1.91 inch PWs respectfully, and
there are surface dewpoints locally in the low to mid 70s helping
to contribute to the elevated CAPE values.

Satellite imagery already shows an expanding CU/TCU field across
areas northern PA and southern NY, with some spotty hints of CI
taking place. Differential heating boundaries coupled with
convergent low-level flow near and south of the front, and also
near a lee-side trough over southern New England will facilitate
the development and expansion of convection over the next few
hours. This will especially be the case over areas of southern New
England as the aforementioned surface wave and supporting energy
aloft begins to arrive while combining with the very moist and
increasingly unstable boundary layer.

Rainfall rates are expected to be locally very high and capable of
reaching 2.5 inches/hour with the stronger storms given the high
PW/CAPE environment. It should be noted too that there is a belt
of stronger mid-level flow over the region with locally 30+ kts of
effective bulk shear that will help to favor some regionally
organized clusters of convection later this afternoon and some of
these higher rainfall rates.

The 12Z HREF guidance supports the heaviest rainfall totals
occurring over southern New England where convection should be
more organized/focused. As much as 2 to 4 inches of rain will be
possible across parts of CT/RI and MA, but at least scattered
areas of showers and thunderstorms are expected farther west
across northern NJ, north-central to northeast PA and
south-central to southeast NY where isolated 1 to 3 inch amounts
may occur with the stronger storms.

Isolated to scattered instances of flash flooding will be
possible, and this will include some urban flash flooding concerns
potentially near and north of New York City through Hartford and
Providence.

Orrison

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

ATTN...WFO...ALY...BGM...BOX...BUF...CTP...GYX...OKX...PHI...

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

LAT...LON   42907282 42607139 42087084 41457119 40997252
            40127361 40027456 40387527 41377660 41697802
            42467814 42887736 42717544 42647418