AWUS01 KWNH 231733
FFGMPD
MEZ000-NHZ000-VTZ000-NYZ000-232330-

Mesoscale Precipitation Discussion 0492
NWS Weather Prediction Center College Park MD
130 PM EDT Sun Jun 23 2024

Areas affected...Portions of Central/Eastern NY into New England

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

Valid 231730Z - 232330Z

SUMMARY...Scattered to broken areas of heavy showers and
thunderstorms this afternoon, including some supercells, may pose
a localized threat for some flash flooding.

DISCUSSION...A rather strong upper-level trough crossing through
the Great Lakes region continues to drive a cold front steadily
eastward toward the Northeast U.S. Strong diurnal heating and a
moist boundary layer out ahead of it has allowed for warm-sector
MLCAPE values to reach locally over 1500 J/kg across central and
eastern NY. This coupled with strong effective bulk shear
magnitudes of 40 to 50+ kts will be fostering the development of
well-organized convection, including supercells heading through
the afternoon hours across areas of eastern NY through VT/NH and
possibly into southwest ME.

While the dominant hazard attached to the convection will be
severe in nature (see latest SPC products), there is likely to be
a sufficient level of convective organization in conjunction with
anomalously high PWs for rainfall rates to be quite elevated with
the stronger convective cores, and especially any of the supercell
activity that does materialize over the next few hours.

The PW in the 12Z RAOB sounding from ALY was 1.89 inches, and
recent GPS-derived data continues to show PWs regionally on the
order of 1.75 to 1.90 inches, and these values are on the order of
2 to 3 standard deviations above normal.

The 12Z HREF guidance supports rainfall rates reaching locally as
high as 2 inches/hour with the stronger cells this afternoon, and
there is a threat for some more concentrated and repeated
convection over areas of VT/NH and possibly southwest ME where
there is also proximity of a warm front attempting to lift
northeastward ahead of the approaching upstream trough and
associated cold front. Generally this region is where the guidance
is the wettest with some spotty 2 to 4 inch rainfall amounts
suggested.

Given the elevated rainfall rate potential with this afternoon's
stronger and more organized convection, a few instances of flash
flooding cannot be ruled out. For some locations this may also
fall over areas that saw some locally heavy rain this morning
which will may help focus some runoff problems.

Orrison

ATTN...WFO...ALY...BGM...BTV...BUF...GYX...

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

LAT...LON 45197136 45027021 44536948 43946953 43517010
43167123 42817251 42897422 43337549 43907570
44247498 44397393 44777313 45047229
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AWUS01 KWNH 041839
FFGMPD
MEZ000-NHZ000-VTZ000-NYZ000-050037-

Mesoscale Precipitation Discussion 0804
NWS Weather Prediction Center College Park MD
238 PM EDT Sun Aug 04 2024

Areas affected...northeastern New York state, northern Vermont,
northern New Hampshire, and portions of Maine

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

Valid 041837Z - 050037Z

Summary...Scattered thunderstorms are producing brief heavy
rainfall and areas of 1-1.5 inch/hr rain rates at times. These
rates are falling on sensitive ground conditions and are likely to
result in instances of flash flooding through the early evening.

Discussion...Scattered thunderstorms have developed across the
discussion area amid a destabilizing airmass (characterized by
2000-2500 J/kg MLCAPE) and weak forcing for ascent aloft
associated mid-level waves over New York. The storms are embedded
in appreciably high PW air (characterized by 1.5 inch PW values)
and only modest westerly steering flow aloft, supporting slow
storm motions (around 10-20 knots). These cores were falling on
locally sensitive ground conditions from prior rainfall over the
past week (particularly near St. Johnsbury and vicinity), and FFG
thresholds (generally in the 1-1.5 inch/hr range) were being
locally exceeded as slow-moving thunderstorms were progressing
through the region.

Much of the flash flood threat across the region should be
diurnally driven, although a lingering threat after dark should
exist with any persistent cells or clusters. Some of the ongoing
convection should gradually merge/grow upscale into
forward-propagating clusters, although the process of
merging/localized training could further bump rain rates into the
1.5-2 inch/hr range at times. Flash flood potential is likely to
persist through at least 23Z this evening.

Cook


ATTN...WFO...ALY...BTV...CAR...GYX...

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

LAT...LON 46726886 46546812 45916789 45266826 44696958
43937245 43717431 44387477 44927436 45017357
45177239 45527127 46007044 46526986
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