Area Forecast Discussion
Issued by NWS Portland, ME

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000
FXUS61 KGYX 262343
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
743 PM EDT Tue Mar 26 2024

.SYNOPSIS...
A weak wave sent from a larger system over the Atlantic will
continue to bring low clouds, drizzle, and rain with some light
icing across the mountains through tonight. While we`ll be in a
bit of a cloudy, mild, and humid lull on Wednesday, a front will
approach from the west and bring increasing chances for rain
late Wednesday through Thursday before exiting on Friday.
Steadiest and heaviest rains are expected on Thursday, along
with significant snowpack ripening or, in the case of the
coastal plain and adjacent interior, significant snowpack melt.
Precipitation may try and end as snow Friday before things
become drier and gusty over the weekend.

&&

.NEAR TERM /UNTIL 7 AM WEDNESDAY MORNING/...
Update...
Drizzle continues to move inland from the Gulf of Maine this
evening per latest radar imagery and surface observations. Areas
of fog continue to develop as well on this raw night with dew
point depressions very low tonight. Fog with visibilities below
a half mile at times will continue throughout the night which is
supported by the latest HREF solution.

A Winter Weather Advisory remains in effect over northern and
western portions of the forecast area. However, temperatures
remain warm in these regions both in the valleys and across the
high peaks as we remain under a sharp inversion as depicted by
the 00Z GYX sounding. We may be able to drop at least some of
the advisories for the overnight period and will continue to
monitor localized trends.

Prev Disc...
Stacked low pressure, quite photogenic on GOES-East this
afternoon, continues to spin well east of Cape Hatteras while
high pressure remains in place over Newfoundland. Northeasterly
gradient flow continues over the New England states as a result,
which keeps a persistent, moderately well mixed, cool and dry
surface layer over the region. Just off the deck and into the
mid-levels however it`s a very different story with an inverted
shortwave trough moving north into Maine, crossing overnight
which will bring a round of light precipitation into the region.

The wave brings an impressive warm nose through the mid-
levels, in stark contrast to cooler surface temperatures largely
a result of the CAD feeding off the maritime high. With this
sort of temperature profile, we can expect cool and calm
conditions under the inversion south of the mountains and
through western Maine... making for a fairly raw overnight with
rain showers, drizzle, and fog for most of the area. The
exception would be in the Connecticut River Valley, and far
southern interior NH where conditions will be a little less
damp.

The biggest question going into tonight in terms of impacts will be
the presence of below-freezing temperatures and associated potential
for icy conditions to develop, as the warm nose aloft leaves no
chance for snow to fall. As of this afternoon, the entire forecast
area is above freezing except for just a few pockets in the
intermountain valleys. For tonight, latest hires model guidance
(leaning heavily on the NAMNest in a CAD situation such as this) has
a fairly limited amount of freezing or sub-freezing temperatures
present this evening, although wetbulb effects from precipitation
falling into the CAD should help cool conditions in any case.
Overall I`m seeing a bit less of a threat for freezing rain and/or
drizzle through the mountains, but with the product already in place
and the tendency for valleys (where people tend to live and drive)
under the inversion to hold onto cold air, I`ll keep the current
Winter Weather Advisory unchanged.

&&

.SHORT TERM /7 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Tonight`s shortwave trough moves north, away from the region on
Wednesday with a brief nosing-in of high pressure in its
wake... wedged between the departing shortwave and a cold front
approaching from the west. Thus tomorrow will be a bit of a lull
in precipitation, although it will still be mostly cloudy with
plenty of humidity remaining in the column. For temperatures, a
warmer airmass will be firmly in place, supporting high
temperatures in the 40s and 50s, warmest where more breaks of
sunshine leads to stronger mixing... mainly in New Hampshire
into southwest Maine.

Later in the evening and overnight, the aforementioned frontal
zone crosses into New Hampshire and eventually to Maine. While
there doesn`t appear to be much in the way of forcing over the
frontal zone initially, it will still support light rain shower
activity... and steadier rains late Wednesday night into early
Thursday as a jet arrives and provides better dynamic support.
More on this system and related impacts below in the Long Term
and Hydrology sections. Would also expect it to be a fairly
soupy, foggy night across the board given very light or calm
winds atop cold (but ripening) snowpack. Mild lows in the 30s
or low-40s mirror expected dew points.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Overview...

A large blocking high centered across the Canadian Maritimes
slowly shifts northeastward through the end of the week as a
trough digs in across the East Coast. A cut off low near Bermuda
gradually drifts further out to sea and weakens through late in
the week. Low pressure develops near the Carolinas Thursday
night and passes offshore through Saturday. The trough lingers
across New England into early next week, and then a ridge begins
to build across the Northeast by midweek next week.

Details...

The blocking pattern and the cut off low continues to stream
moisture into New England on Thursday, with a stalled frontal
boundary in place near the East Coast. This keeps showers and
periods of light rain ongoing across the area, especially closer
toward the coastline. There remains some uncertainty on exactly
where this focus of the heavier rainfall will end up, with some
model differences on where the focus will be. Global models
show the focus closer to the coast, and high res guidance
pointing toward the focus being further west into the mountains.
There becomes a greater concern the farther inland the heavier
rainfall progresses, where there is a greater snowpack.

This concern continues into Friday and Saturday as low pressure
develops near the Carolinas and tracks through the Gulf of
Maine. Currently most of the model guidance shows the bulk of
the moisture from this system passing offshore, but not by very
far. It`s not out of the question that this system trends a
little closer to the coastline, and would then raise greater
flooding concerns. The inland snowpack is likely to absorb most
of the rainfall through Thursday, but anything beyond that would
lead to more melt and runoff. At this point the ensemble trend
has been toward a slightly drier solution with the system
staying farther offshore, which is favorable to lessen the
flooding risk, but we will continue to monitor to see is this
trend continues.

By Saturday, the system will be pulling away as high pressure
builds into New England. Breezy conditions are likely behind
this system starting late Friday, and continuing on Saturday.
The high continues in build in through the weekend, with a ridge
and a bit more of a warming trend toward next Tuesday. The next
system is then likely to track eastward toward the Northeast by
the late Tuesday to Wednesday timeframe next week.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Short Term...Widespread IFR and LIFR overtakes the region this
evening, mostly with CIGs but also with VSBY late tonight as FG
develops over the coastal plain into the interior... and as NE
winds AOB 15 kts persists. DZ and SHRA will also be present
during this time. The CT River Valley (KHIE, KLEB) will take
longer to see significant restrictions, especially KHIE which
may not see low CIGs fill in until late tonight/early Wed if at
all. Significant restrictions continue into Wed, with VSBY and
some CIG improvement through late morning but lowered CIGs
likely hanging through most of the day especially in Maine.
Widespread IFR/LIFR is expected to develop again Wed night.

Long Term...MVFR to IFR conditions likely prevail with showers
and periods of light rain for Thursday into Friday at most
terminals, with western terminals seeing better conditions
overall. Eastern terminals see restrictions linger into Saturday
as western terminals improve. Gusty conditions with
northwesterly gusts to 30kts are likely on Friday into Saturday.
VFR conditions return by late Saturday and persist into early
next week.

&&

.MARINE...
Short Term...Gusty northeast winds diminish this evening, and
become light AOB 15 kts Wed and Wed night. Seas in the meantime
will remain elevated, at 8-13 ft, highest along southern
coastal waters... and gradually diminishing below 10 ft on Wed
and closer to 5 ft Wed night.

Long Term...A front stalls across the waters on Thursday, with
SCA conditions continuing through at least Friday. Low pressure
tracks across the eastern waters Friday and Saturday, with
northwesterly gales possible Friday night and Saturday as the
system passes by. High pressure returns by late in the weekend,
with conditions falling below SCA levels by late in the weekend

&&

.HYDROLOGY...
The snowpack is likely to melt out across the coastal plain
this week as periods of light rain and showers fall across the
area. River rises are expected, and some minor flood can`t be
ruled out by late this week and into the weekend. Areas further
inland and across the mountains can likely handle up to about
1.5" of rainfall, with most of this being absorbed by the
snowpack. Beyond that amount, runoff will begin to increase and
flooding would become a greater concern. The best chance for
exceeding this rainfall would come from a system passing
offshore on Friday. At this point the heaviest rainfall is
forecast to remain offshore, but this will need to be monitored
for any trends toward higher amounts, which would increase
flood concerns.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory until 8 AM EDT Wednesday for
     MEZ007>009-012-013.
NH...Winter Weather Advisory until 8 AM EDT Wednesday for
     NHZ002>006-008-009-015.
MARINE...Small Craft Advisory until 8 PM EDT Wednesday for ANZ150-
     152>154.

&&

$$
Cannon/Clair


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