Subj : MESO: Nws Weather Prediction Center College Park Md
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Fri Jun 20 2025 00:30:54

AWUS01 KWNH 200030
FFGMPD
MEZ000-NHZ000-200600-

Mesoscale Precipitation Discussion 0487
NWS Weather Prediction Center College Park MD
830 PM EDT Thu Jun 19 2025

Areas affected...Northern Maine...Northern New Hampshire...

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

Valid 200030Z - 200600Z

SUMMARY...Strong squall line with up to 2"/hr rates with scattered
upstream cells capable of repeating through areas affected
initially.  Localized totals to 2-3" by 06z, continuing risk for
localized flash flooding into the early overnight period.

DISCUSSION...RADAR starting to show squall line taking on more
embedded bowing segments as the line reaches the lifting warm
front across northern ME and the instability gradient.  Subtle
shortwave, weak height-falls driving the low level
backed/convergent flow continues to lift northeast into the
upriver portions of the St. Lawrence Seaway.  As such, forward
propagation speeds are starting to flatten the convective line
allowing for increased heavy rainfall duration.  Given total PWats
still in the 1.75"+ range and ample remaining MLCAPE convective
line is likely to maintain capability of 1.5-2"/hr rates and with
increased duration of training, 1-2 hours may start to result in
localized 2-3" totals along the band.

While the deep layer moisture is exiting with the wave/drying
slightly upstream, the LLJ is strengthening with winds increasing
from 25-30kts toward 35kts, favoring upwind convergence.  This may
support flanking line/back-building development with time.
Also, given the lingering west to east outflow boundary upstream
is also orientating favorably for some increased orthogonal
isentropic ascent in the upstream unstable airmass over NE NY into
VT (as well as clusters in S Quebec near the surface boundary),
will allow for additional development to potentially repeat across
areas that have been recently saturated.   As such, widely
scattered/localized flash flooding remains possible through the
early overnight period across Northern NH and ME.=20

Gallina

....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!7KRPftpJHxuycNIoO_CWAclCdjsqFHX5y2lpqMgEWzp3ZNCllrAM6bTII5bTJTiDsTKG=
OuS7phihPTOMY_-shXw3LRY$  for graphic product...

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

ATTN...RFC...TAR...NWC...

LAT...LON   46916783 45866769 45536779 45326825 44876933=20
            44457021 44287146 45027140 45357115 45567081=20
            46127039 46667004 46906933=20

=3D =3D =3D
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