Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 281322
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
922 AM EDT Sat Mar 28 2020

.SYNOPSIS...
High pressure crosses the area today with another mostly sunny
and warm day expected. A warm front lifts north toward the area
tonight, and by Sunday morning snow is expected to spread across
much of the area...with rain across southern New Hampshire. The
heaviest snow and sleet accumulations will be in the western
Maine mountains where a Winter Storm Watch has been issued. Snow
mixes with or changes to rain for much of the remainder of the
area on Sunday. As low pressure slowly exits, showery weather
will continue into Monday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

920 AM...at 13z a 1022 millibar high was centered over western
New England. a warm front extended from the upper Midwest
through the central Appalachians to North Carolina. For today...
sunshine will begin to fade during the afternoon as high and mid
clouds begin to spill over the top of the ridge into the
forecast area. NWS Doppler Radar mosaic showed a large area of
precipitation to the north of the warm front that stretched
from the lower Lakes through mid Atlantic. This activity will
spread east with some light rain possible in far southwest New
Hampshire by evening. Otherwise a warm and dry day on tap with
highs in the 50s...except upper 40s along the international
border. For this ESTF update...minor adjustments to near term
grids to reflect current satellite and radar trends as well as
the 13z mesonet.


Prev disc...
730AM UPDATE...
Adjusted hourly temperature forecast based on early morning
observations. Mostly clear sky with passing cirrus this morning
will lead to increasing clouds as the day goes on.

ORIGINAL DISCUSSION...
High pressure crosses the area today. Winds will be light or
even calm. We warm into the 50s again with strong sunshine. This
will likely lead to a sea breeze developing on the coast as the
waters are still very cold.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Clouds increase tonight as a warm front lifts toward the area.
Some light precipitation could begin before daybreak in
southwest New Hampshire. Temperatures will be slow to cool with
the cloud cover, but as precipitation begins it will be falling
into a dry air mass and bring the temperatures down due to
evaporational cooling.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
A trough aloft will move east over the next 24 hours bringing low
pressure with it. As the low pressure moves through the Great Lakes
a warm front will move into our region. There is good agreement
on the timing on the precipitation onset and expect it to first
move into southwest NH around 12Z Sunday. From there it will
rapidly spread northeast across the CWA through the morning.
While precip seems certain the precipitation type is much less
certain.

While departing high pressure and surface wind direction would
suggest some possibility for damming, the persistent warm
temperature over the past few days make it unlikely that
surface temperatures will be cold enough for snow initially.
Instead what will help the snow along is the dry lower levels.
This will allow the wet bulb effect to take over and actually
expect temperatures to drop as the precip begins to fall and
thus changes over to snow. While that is the surface story,
aloft we still have to consider the potential for the warm layer
to move in. Across southern New Hampshire expect this to be
well entranced with the result being mostly rain. From Portland
through to Concord and north, forecast soundings show an
isothermal layer and some sleet is possible at onset. Finally in
the northern mountains temperatures remain cold enough for all
snow. For both the surface temperatures and dewpoint have
favored the NAM which gives a colder drier start to the system.

The result of all of these competing factors is a large
gradient in snowfall across the region. Along the Canadian
border, as much as 6 inches of fairly dense snow is expected
while along the southern border accumulation remains zero.
Overall with this package have shifted the light accumulations
further south as I feel the wet bulb may allow for minimal
accumulations, however heavier snowfall remains confined to the
north consistent with prior forecasts.

With a solid 6" across most of the northern zones have issued a
winter storm watch. While the higher elevations of Coos may also see
significant snowfall, the CT valley will likely remain warm and so
have opted to keep this zone out of the watch.

As we move into Monday the main low moves out of the way and we
remain in wrap around precip as the upper low begins to stall
overheard. Expect showers to continue with some minimal additional
accumulation in the north.

By Tuesday we finally see the upper low start to depart, with a few
breaks in the clouds possible by afternoon. Temperatures will warm
slightly through midweek.  Another low looks to remain south of us
with the cloudy conditions persisting through the end of the week.

Through out the week a blocking high remains to our east over
the Atlantic, and the potential for us to remain trapped under
the upper low with scattered shower activity makes for an
unsettled and uncertain forecast through week`s end.

&&

.AVIATION /13Z SATURDAY THROUGH WEDNESDAY/...
Short Term...VFR conditions today with light and variable winds.
Could see a sea breeze develop at the coast this afternoon.
Increasing clouds expected this evening with lower ceilings and
light precipitation beginning in southwest New Hampshire. Will
likely see MVFR and IFR conditions developing by Sunday morning.

Long Term... Sunday will bring widespread precipitation with IFR
conditions expected to develop from southwest to northeast through
the morning as a mix of snow and rain moves through. Fog developing
overnight will keep the IFR through Monday morning. Thereafter
unsettled weather will keep showers and MVFR in the mountains
through the first part of the week.

&&

.MARINE...
Short Term...High pressure crossing the waters today brings very
light winds.

Long Term...Expect SCA under easterly flow as the warm front approaches
and lifts northwards on Sunday.  Fairly calm conditions for the
waters this next week as unsettled weather from the low overhead
remains in place. Several times conditions may approach SCA but
confidence is low on the timing.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Watch from Sunday morning through Monday morning
     for MEZ007>009.
NH...None.
MARINE...None.

&&

$$

ES


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