256
AWUS01 KWNH 102349
FFGMPD
MEZ000-NHZ000-VTZ000-NYZ000-110600-

Mesoscale Precipitation Discussion 0604
NWS Weather Prediction Center College Park MD
747 PM EDT Wed Jul 10 2024

Areas affected...portions of the Northeast/northern New England

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

Valid 110000Z - 110600Z

Summary...Tropical moisture associated with the remnants of
post-tropical Beryl to continue to fuel extreme hourly 1-3"
totals. This is expected to result in additional totals of 3-5".
Numerous to widespread flash floods are likely, including some
significant, life threatening flash flooding.

Discussion...The remnants of post-tropical Beryl and the base of
an associated upper-level longwave trough are gradually shifting
northeast, currently located over eastern MI and Lakes Huron and
Erie. Strong to severe thunderstorms have been concentrated along
a warm front and associated secondary low pressure center, which
extend northeastward from the main cyclone triple-point (located
over western NY). The mesoscale environment in the vicinty of the
secondary low pressure center and associated warm front is
characterized by ML CAPE of 1000-2000 J/kg, precipitable water
values of 2.1-2.4 inches (near all time record values, per ALB
sounding climatology), and effective bulk shear of 45-65 kts. In
addition, a broad 30 kt low-level jet (LLJ) at 850mb is progged to
narrow and intensify to 35-45 kts this evening (per the 21z RAP
forecast), driving ample moisture transport/flux convergence. This
strong low-level convergence is also being complemented by even
more significant divergence aloft (~250 mb), via the
right-entrance region of a 110+ kt jet streak over southern
Quebec.

Hi-res guidance paints an especially concerning picture through
evening, as localized hourly totals of 1.5-2.5" (per MRMS
estimates) are expected to continue in association with
semi-discrete supercell/multicell clusters (with instantaneous
rainfall rates of 4"/hr resulting in as much as 1" of rainfall in
15-min). While these hourly totals have remained somewhat
localized thus far, the increasing coverage of cells (as the
aforementioned dynamic aspects of the system continue to improve
this evening) is already resulting in numerous to widespread
coverage along and ahead of the warm front. This should result in
a swath of 3-5" of rainfall from northern NY through northern
VT/NH, with very good agreement among the hi-res guidance (18z
HREF members and more recently hourly runs of the HRRR). A narrow
swath of these totals has already occurred across portions of
northern NY, which suggests that locally higher amounts (6"+) are
rather likely as well (which is depicted by the most extreme HREF
members, as well as the 90th percentile of the experimental WoFS
system). Perhaps the most telling piece of statistical guidance is
the HREF neighborhood (40-km) probability for 100 year Annual
Recurrence Interval (ARI) exceedance, which ranges from 30-50%
(outlined by the pink hatched area in the graphic). Given this
totality of data, numerous to widespread instances of flash
flooding are likely (and locally significant, life threatening
flash flooding is also likely, particularly over vulnerable
low-lying areas in the vicinity of 6"+ totals).

Churchill

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

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

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

LAT...LON   46297009 45636965 44157111 43277346 42767532
            43347614 44667455 45447270 45937133