Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 221403 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1003 AM EDT Fri Mar 22 2024

.SYNOPSIS...
A cold and blustery day is expected today. A low pressure system
arrives in New England on Saturday, bringing heavy snow, wintry
mix and rain to the region. Significant snowfall is expected
across interior Maine and northern New Hampshire. Afterwards,
tranquil weather is expected at the start of next week with
temperatures progressively getting warmer through the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1000am Update: Only some minor tweaks to align
sky/temperature/dew point trends with morning observations...but
no other changes to the forecast at this time. Very dry airmass
evident on the 12Z GYX RAOB /PWAT 0.06"/ with northwesterly
winds gradually diminishing as high pressure builds in from the
west. Will await the full suite of 12Z guidance before making
the final call on winter headlines across the watch area and to
its south.

7:40am Update... Just a quick update for today based on trends
so far this morning, but there have been no notable changes as
the forecast remains on track at this time.

Previous...

High pressure crests across New England today, bringing
diminishing winds and mainly sunny skies. A seasonably cool day
is expected, with highs ranging from the mid 20s across the
north to near 40 through southern New Hampshire. High clouds
begin to filter into western areas late this afternoon as our
next storm system approaches.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
An intense shortwave moving through the northern stream of the
jet crosses through the Great Lakes and then the Northeast
tonight through tomorrow night. At the same time, rich moisture
from a moisture laden low pressure system moves up the Eastern
Seaboard, with moisture originating from the Gulf of Mexico and
off the Southeast US coast and getting drawn into the
shortwave. Low pressure gradually deepens and track through the
Gulf of Maine through tomorrow night, but a 1004mb low isn`t
typically what one might expect to bring over a foot of snow to
parts of the area. So it is a somewhat unique set up that is
expected to bring widespread and significant snow, mixed precip,
heavy rain, and the threat of flooding closer to the coast.

Snow likely begins to break out from southwest to northeast
shortly after midnight tonight, spreading to the coastline
during the predawn hours. An initial burst of snow and then a
brief lull looks likely, and then the steadier and heavier
period of snow gets underway by sunrise on Saturday. Heavy snow
is expected through much of the interior and the mountains, but
a transition to sleet and freezing rain begins to work its way
inland from the coastline and into southern New Hampshire by
mid-morning. This continues to progress inland through the
daytime, but just how far inland remains a major question. Plain
rain is also likely as temps warm along the immediate
coastline, and then the question of how far inland this moves
also arises.

Overall the overnight global model guidance continued to trend
colder, continuing the trend seen late yesterday. However, the
high res guidance is generally warmer, and hasn`t trended much
away from this idea. The HRRR and the NAM are some of the
warmest solutions, showing mixed precip up the Canadian border,
and rain all the way to the foothills and White mountains. While
not out of the question, there is a general belief the global
models are better equipped to handle a system like this and are
less prone to feedback errors owing to convection and the
complexity of the jet streak involved with the shortwave.
Because of these factors, this forecast has hedged toward the
colder guidance trend seen in the global models, but stops short
of bringing the significant icing amounts to the coastline,
which is shown on the global models. It`s certainly not out of
the question that the high res models might be onto something
and the track does shift warmer and farther west, so this
forecast allowed some room for this possibility, but has not
trended in this direction.

It`s worth noting that even the coldest guidance brings temps
above freezing aloft all the way to the edge of the mountains,
bringing in sleet and keeping snow totals down somewhat. This
effect increases with southward progression, with areas near the
Canadian border standing the best chance to remain all snow.
Dry and cool air ahead of the system will allow for cold
temperatures at the surface, so only to the east of the coastal
front are temperatures expected to rise above freezing. Exactly
how far inland the coastal front reaches remains a question, and
will be highly dependent on the track of the system. The
current forecast accounts for the front making it about 20-30
miles inland, while the global models are showing closer to only
about 10 miles inland. There will be a sharp temperature
gradient across the front, with temps on the cool side likely in
the mid to upper 20s, and in the mid 30s on the warm side. This
forecast stops short of trying to resolve that gradient at this
point.

By the evening hours, winds shift to more northerly and cooler
air works its way back to the coast. This means that even areas
that change to rain likely change back to mixed precip or snow
for at least a few hours before the storm comes to an end. The
storm then pulls away after midnight, with precip coming to an
end from west to east by daybreak on Sunday.

Winter storm warnings have been issued for the areas where
there is currently the highest confidence for significant snow
total and/or mixed precip. The watch remains for the areas that
are still at risk of transitioning to rain should the high res
guidance come to fruition. However, even in the watch area
travel impacts at a minimum are expected as snow and mixed
precip falls through at least Saturday morning. So we will allow
for a little more time to try to discern whether it is more of
a warning level or advisory level system for these areas.

Along the coast, a flood watch has been issued for the 2-3" of
QPF expected to fall. Any snow or mixed precip that falls along
the immediate coast would be expected to melt with heavy rain in
the afternoon. Any snow clogged storm drains or recently frozen
ground will only add to the flooding concerns.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
The NBM was employed to populate the extended portion of the
forecast with little changes as we concentrate on the storm in
the near term. In short, fair weather returns Sunday with gusty
winds. Thereafter, the next chance of meaningful precipitation
arrives midweek. Temperatures will be near to below normal
through the period.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...

Short Term...VFR conditions are expected through this evening.
Then, conditions lower to IFR and LIFR in snow shortly after
midnight through daybreak from western to eastern terminals,
respectively. IFR to LIFR conditions prevail tomorrow with snow
across inland terminals. Sleet, freezing rain, and rain are
likely for a time across southern and coastal terminals late
tomorrow morning and afternoon. IFR to LIFR conditions continue
through shortly after midnight, and then improvement to MVFR is
expected from west to east through daybreak on Sunday.

Long Term...
VFR prevails Sunday into early next week with gusty winds on
Sunday diminishing thereafter.

&&

.MARINE...
Short Term...Gales ease early this morning, subsiding last
across the eastern waters. SCA conditions linger into the
afternoon, and then a brief period of fair conditions are
expected as high pressure crosses the waters. A developing low
pressure system tracks up the Eastern Seaboard and through the
Gulf of Maine through tomorrow night, with southerly gales
possible across the offshore waters tomorrow, and then northerly
gales possible behind the system late Saturday night.

Long Term...
Gales Sunday and Sunday night diminish Monday as a storm system
moves farther away from our region.

&&

.HYDROLOGY...
A flood watch has been issued for southeastern NH and the coast
of Maine. Rainfall amounts of 1 to 2 inches will likely cause at
least minor urban and small stream flooding Saturday afternoon
into the evening hours. Mainstem rivers will likely OK, as
wintry  and colder temperatures are expected inland.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Warning from 2 AM Saturday to 6 AM EDT Sunday for
     MEZ007>009-012>014-033.
     Winter Storm Watch from late tonight through late Saturday
     night for MEZ018>022.
     Flood Watch from Saturday afternoon through Saturday evening
     for MEZ023>028.
NH...Winter Storm Warning from 2 AM Saturday to 6 AM EDT Sunday for
     NHZ001>006.
     Winter Storm Watch from late tonight through late Saturday
     night for NHZ007>010.
     Flood Watch from Saturday afternoon through Saturday evening
     for NHZ010-012>014.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for
     ANZ150>152-154.

&&

$$


NEAR TERM...Arnott


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