Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Mon Dec 18 2023 20:19:37

AWUS01 KWNH 182019
FFGMPD
MEZ000-MAZ000-NHZ000-190117-

Mesoscale Precipitation Discussion 1208
NWS Weather Prediction Center College Park MD
318 PM EST Mon Dec 18 2023

Areas affected...Portions of Northern New England

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

Valid 182017Z - 190117Z

SUMMARY...Additional heavy rainfall is expected to maintain a
threat of areal flooding and flash flooding across areas of
northern New England through early this evening.

DISCUSSION...The latest surface analysis shows an elongated, but
very deep area of low pressure advancing rapidly northward up
across New England which continues to favor organized areas of
heavy rainfall advancing inland up across areas of New Hampshire
and Maine.

A very dynamic setup remains in place with a coupled upper-level
jet structure overhead favoring extremely impressive deep layer
ascent which combined with very strong warm advection/isentropic
lift and moisture transport continues to favor very efficient
rainfall processes for locally enhanced rainfall totals. The 12Z
GFS shows IVT values of as much 1500+ kg/m/s aimed into the
coastal areas of southwest Maine and reflective of strong
atmospheric river conditions coming in off the Atlantic Ocean. The
low-level jet alone is on the order of 60 to 90 kts which is
yielding extremely impressive moisture transport magnitudes to
support the ongoing heavy rainfall event.

The instability across the Northeast has been modest at best all
day, but there is a pool of MUCAPE on the order of 100 to 250 J/kg
up across central/southern New Hampshire and much of central and
southern Maine. This extra bit of instability is still favoring
some convective elements within the regional clusters of heavy
rainfall and is supporting some occasional rainfall rates reaching
1"/hour.

An additional 1 to 2+ inches of rain will be possible and
especially across the southeast facing slopes of the northern
Appalachians including the White Mountains. This rainfall on top
of the earlier rains will continue to foster rather widespread
concerns for areal flooding and flash flooding, and especially
with areas of rapid snowmelt ongoing given the very warm
temperatures surging north ahead of the low center.

The heavy rainfall threat should rapidly diminish by later this
evening as the deep low center rapidly exits the Northeast, and
this will allow for conditions to then improve across the region.

Orrison

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!71xynanYbyS6aRvtiTy8xJpr3kzWeXcNXDvisVLxPXSOBiCeA3UlrA1eeUTSHvqYWYde=
S2xN1IErYTx8rBAfurvpn70$  for graphic product...

ATTN...WFO...BOX...CAR...GYX...

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

LAT...LON   46816861 46496790 45836793 45156818 44296900=20
            43577017 42707096 42737159 43347179 44847109=20
            46326975=20

=3D =3D =3D
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