Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 120344
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1044 PM EST Mon Dec 11 2017

.SYNOPSIS...
After a cold night tonight, low pressure will move toward New
England from the west on Tuesday. This will spread snow across
the area to start the day, changing to rain along the coastal
plain. Low pressure moves off to the northeast Tuesday night and
an Arctic cold front pushes east across the region early on
Wednesday. This will put northern New England in the deep freeze
as the temperature will likely stay below freezing into the
weekend. The next significant low pressure system is expected to
track off the New England coast Sunday night into Monday,
bringing another chance of snow.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Update...
Quick update to further tweak temperatures, dew points and the
near term wind forecast. A cold front crossed the region today,
allowing for temperatures to drop rather quickly in the
mountains. Have lowered readings in the mountains by several
degrees based on current observations and trends. Thereafter,
clouds increase and thicken, slowing any radiational cooling.

There is a significant amount of cold air to our north with PQI
as the coldest reading late this evening at 9 below zero. A
northeast flow has develop across the interior and some of this
cold air will be funneled southward.

00Z guidance arriving with a slightly colder scenario as well.
The coastal front should be well established by daybreak
Tuesday. Have upped snowfall amounts in the Midcoast region and
the rest of the coast will need to be examined for potentially
higher snowfall accumulations if trends continue.

Chances for precipitation: Echoes on radar continue to move east
towards Maine and New Hampshire. However, plenty of dry air in
place will allow for sublimation for several more hours before
the snow arrives in southern New Hampshire later tonight.

Prev Disc...
For tonight, temperatures will drop into the single
digits to lower teens north with upper teens and lower 20s
south. Increasing cloud cover moves in rapidly tonight. High
pressure gradually shifts away as low pressure approaches from
the west.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Main Concerns...

**Heavy Snow expected for much of the area by rush hour Tuesday
 morning and continuing into the Tuesday afternoon rush hour***

**An Arctic air mass ushers in much colder air by Tuesday
 night***

A dynamic weather system now moving into the western Great Lakes
will be approaching the region very late tonight. Low pressure
at the surface will deepen and reorganize over the NH/ME border
with models agreeing on a 989MB low deepening to near 984MB by
late tomorrow evening.

Confidence is high that this storm will produce heavy snow for
much of the foothills and mountains. However, as the storm deepens,
a coastal front will draw warmer air north changing snow
quickly over to rain for the coast and portions of inland NH and
ME. Thus mesoscale nuances will make or break forecasted
snowfall amounts. The coast and areas just inland may see mostly
rain from this event. Farther inland...including interior
southern NH and Maine, we will see closer to 3-6" of snow with
colder temperatures in place. Even farther north there will be a
sharp uptick in snowfall amounts where colder air is currently
(and will still be) dammed north of the higher terrain. In this
area expect widespread 8-12" inches. Watches have been converted
to warnings and advisories accordingly.

Other concerns with this forecast include temperatures falling
across much of NH and northern ME Tuesday night into the teens
by daybreak as the Arctic front sweeps eastward with time.
Depending on the timing and how fast this occurs, a flash freeze
may be a concern for areas that receive rain. Winds will be
gusty tomorrow night with the system wrapping up and lifting NNE
as a dry slot works in from the SW. Additional snow is likely
for the mountains as it lifts out.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
A strong cold front pushes east across the area on Wednesday.
High temperatures will likely be around sunrise with
temperatures falling sharply behind the front. With cold
advection and deep mixing, winds will be gusty as well, with
gusts to 30 MPH likely and 40 MPH possible. This will make it
feel even colder, with wind chill values dropping below zero by
Wednesday evening into Wednesday night.

A shortwave trough tracks quickly east well to the south of New
England on Thursday, far enough south to avoid any impacts in
our area. Temperatures will be cold, generally in the 20s for
highs. High pressure builds in for Thursday night bringing
decent radiational cooling conditions, so expect lows in the
single digits above and below zero.

The next trough moves by on Friday/Friday night. The GFS would
have us believe that this will cause a surface low to track
close enough to bring snow to the coast, but it appears to be
the outlier among the models and within its own ensembles.
Therefore will not put too much weight into that solution and
keep the forecast mostly dry.

In the wake of the Friday night trough, models are rather
inconsistent on the details of the various waves within the
westerly flow. It is possible that a wave could move by Saturday
or Sunday but it won`t have much moisture with it so if
precipitation does occur it would only produce light snow.

The next more substantial wave moves up the northeast US coast
Sunday night into Monday. This track would put our area in the
sweet spot for another round of snowfall. The GFS is a littler
further east with the track, so it is colder and a bit drier,
while the ECMWF brings heavier precipitation and a low track
close enough to the coast to think about a rain/snow line.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
Short Term...Expect conditions to rapidly deteriorate to IFR
early Tuesday morning generally from west to east with periods
of LIFR in heavy snow expected for New Hampshire between 12Z
and 20Z and into central and northern Maine from 15Z-00Z.

Long Term...Conditions should go to VFR behind a cold front on
Wednesday, with the exception of the northern mountains where
MVFR/IFR ceilings and light snow may continue. Winds on
Wednesday will gust up to 30KT behind the front. Mostly VFR
conditions expected into the weekend.

&&

.MARINE...
Short Term...Have discontinued the SCA for this evening in
favor of issuing gale warnings for all marine zones beginning
Tuesday morning as a strong low pressure system moves through.

Long Term...A cold front crosses the waters early Wednesday with
winds gusting to 40KT or so behind it. Westerly flow may not
fall below advisory levels until Thursday night as high pressure
builds in. Low pressure will track northeast through the western
Atlantic on Friday night into Saturday, and it could come close
enough to provide stronger north to northeast winds for a time.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Warning from 4 AM Tuesday to 1 AM EST Wednesday
     for MEZ007>009-012>014.
     Winter Weather Advisory from 4 AM Tuesday to 1 AM EST
     Wednesday for MEZ018>022.
NH...Winter Storm Warning from 2 AM Tuesday to 1 AM EST Wednesday
     for NHZ001>006.
     Winter Weather Advisory from 2 AM Tuesday to 1 AM EST
     Wednesday for NHZ007>011-015.
MARINE...Gale Warning from 10 AM Tuesday to 1 AM EST Wednesday for
     ANZ150>154.

&&

$$
Cannon



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