Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Mon Jul 10 2023 22:00:09

AWUS01 KWNH 102200
FFGMPD
MEZ000-NHZ000-VTZ000-NYZ000-110400-

Mesoscale Precipitation Discussion 0693
NWS Weather Prediction Center College Park MD
558 PM EDT Mon Jul 10 2023

Areas affected...Northeastern NY...Vermont...New
Hampshire...Western ME

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

Valid 102157Z - 110400Z

SUMMARY...Additional heavy rain is expected across highly
saturated ground during the evening hours with some increase in
intensity and coverage through midnight local time.  Flash
flooding is likely across much of Vermont and into far
northeastern New York and western New Hampshire, and possible
across most of central/eastern New Hampshire and into far western
Maine.

DISCUSSION...A well developed and anomalous upper low is present
across central NY with a deep plume of moisture advection ahead of
it across the northern Appalachians.  An 850 mb low has also
developed across southern Vermont, and this is resulting in
stronger southeasterly low level flow oriented generally
orthogonal to the terrain, and deep layer southerly flow in the
700-300 mb layer advecting PWs on the order of 1.6 to 1.9 inches
per recent SPC mesoanalysis.

One of the migitating factors so far has been the relative lack of
significant instability late this afternoon with mixed layer CAPE
generally below 500 J/kg, owing mainly to persistent cloud cover
across the region.  This is generally keeping observed rainfall
rates under 1 inch per hour for most areas.  However, highly
efficient warm-cloud rainfall processes are at work, and
warm-cloud layer depths are in excess of 12,000 feet in some
cases.=20

Much of this region has already been hammered by excessive
rainfall over the past several days, with 7 day observed rainfall
on the order of 300-500% of normal across much of the outlook
area.  The latest HREF neighborhood probabilities indicate a
20-30% chance of 6-hourly QPF reaching 100 year ARI values along
the NY/VT border near Lake Champlain, and this would indicate the
potential for serious flash flooding concerns if storms with
higher rainfall rates can develop and persist.  HREF neighborhood
probs also indicate up to a 60% chance of flash flood guidance
exceedance for the same general area and into central portions of
Vermont.  Flash flooding is considered likely given the saturated
antecedent conditions and favorable meteorological set-up.

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!9eBpx8HcGZZ8XvHwa15Yfm3r8cVzuicaUHMtdID39Pf7xKiGLrEYGN8cuZtJ6ApfUceP=
e0TEH5eSP0bBNPHuoEkiekA$  for graphic product...

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

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

LAT...LON   45537093 45437041 44557066 43817094 43357127=20
            43117155 42997190 42897231 43017281 43097342=20
            43317388 43617397 44007409 44357453 44817461=20
            45037417 45067338 45077240 45087168=20

=3D =3D =3D
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