Area Forecast Discussion
Issued by NWS Portland, ME

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541
FXUS61 KGYX 171726 AAC
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1226 PM EST Fri Jan 17 2020

.SYNOPSIS...
Low pressure track northeast of the Canadian Maritimes today and
tonight. Northwest continues today with cold air continuing to
flow into the area through tonight. The next storm system
arrives Saturday night into early Sunday with more accumulating
snow likely for much of the area. Cold high pressure builds in
for the beginning of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1225 PM Update...
Temperatures were lowered slightly for several locations as we
struggle to make much headway in cold air advection today. Winds
are still quite gusty between a strong pressure gradient with
low pressure to our north and vigorous mixing. Temperatures
have come up enough to be out of wind chill advisory danger for
all but the highest peaks. Will be evaluating this threat once
again for later this evening before winds drop off.

910 AM Update... Have updated to remove the wind chill advisory
and wording from products. Temperatures have increased enough
over the north country to do so with wind chills around -10 to-
15F for the most part this hour. Otherwise made some minor
adjustments for current thermal trends.

625 AM...Added patchy blowing snow through early afternoon to
the whole CWA. Reports are the usual roads near open areas are
getting snow covered in the wind. I think the wind will surge a
bit higher this morning, but should come down gradually after
midday. Otherwise, just the usual adjustment based on current
obs for the next few hours.

Previously...Strong pressure gradient will persist across the
CWA today as sfc low continues to deepen to our east, and strong
high pressure /~1050 MB/ slowly creeps in from the west. This
will keep the NW winds going today, gusting to 30-35 mph,
especially this morning. This combines with continued strong CAA
will produce highs from 5-10 above in the mtns, and around 20
in the S, but daytime wind chill will range from -10 to -15 in
the N to around zero in the south. Still, should see mainly
sunny skies, even in the mtns by this afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
The sfc high, although weakening a bit, will shift in from the
west tonight. Lows tonight will depend on how quickly decoupling
occurs, as there will likely be some NW boundary layer flow
through the evening, so may not see full a full rad cooling
with fairly fresh snow cover, but still, the second half of the
night should push the entire CWA close to or below zero, with
lows in the mtn valleys possibly closing in on -20 F.

Light flow early Sat will shift to the S-SE in the afternoon,
and will see clouds thicken and lower from the SW, with snow
developing mid-late afternoon across all of NH and possibly wrn
ME. The heaviest snow will likely hold off until after sunset.
Highs will be in the teens N, to low-mid 20s S, and will likely
not change too much during the afternoon.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
*** Widespread snowfall expected Saturday night ***

A progressive pattern looks to set up over North America for
 the next week. Looking to our west we can see the start of
what will become Saturdays storm forming. A broad open leaf is
visible on water vapor imagery over Colorado. This will combine
with the short wave moving out of the Oakanagan valley of BC
with pressure falls currently observed over eastern North
Dakota.

By Saturday afternoon expect a robust low pressure system over the
Great Lakes starting to spread a cloud shield into western New
England. This low pressure will rapidly cross southern Ontario and
then northern Maine Saturday night into Sunday as it begins to
occlude.

With cold high pressure in place before the arrival of the storm
expect a strong coastal front to set up as the storm approaches
keeping all of the land areas below freezing with only the NH
seacoast at risk for mixing. Snow will move in rapidly Saturday
evening. Forecast soundings show strong upward motion through the
snow growth region from 00Z-06Z Sunday, and we may see snowfall
rates of 1"/hr+ during this time. With the progressive nature of the
system the intense snowfall rates won`t last long, limiting the
accumulation. Overall expect the snow accumulations to remain right
around the 6" warning threshold, with the highest confidence of
exceeding that from Portland to the Lakes Region of NH and back
through the Maine foothills and Augusta. Across southern NH the
warming trend aloft may decrease snow ratios, while in far northern
NH the CT Valley will likely be shadowed on the front side of the
system. With totals hovering right around the Winter Storm Watch
threshold have opted to hold off on a Watch for this update in hopes
that time will allow for a better idea of the focus of the heaviest
snowfall.

By Sunday morning we`ll already see the backside of the system
moving in. As conditions dry out aloft expect a brief period of
Freezing drizzle on Sunday morning before the precipitation is
able to completely come to an end. By Sunday afternoon
increasing W to NWly flow will bring wind gusts to around
25-30mph across the region as the low continues to intensify and
move into the maritimes.

As we move into the start of next week a very cold air mass will
move south out of Canada. Arctic front will cross the region on
Tuesday with snow squalls possible along the leading edge. sub
zero low temperatures will drop right to the coast.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Short Term...Some lingering MVFR in the mtns and at RKD through
sunrise, but should be mainly VFR thru much of Saturday. NW
wind gusts in the 25-30 kt range are still possible through
today.

Long Term...Snow will move in Saturday afternoon in western NH
and quickly cross into ME. Expect conditions to rapidly
deteriorate to IFR in snow with IFR possible at times.
Conditions will improve as quickly as they dropped with VFR
returning to all but the mountains. Upslope snow showers will
keep the mountains in MVFR through the end of the weekend. Cold
high pressure builds in for the start of next week.

&&

.MARINE...
Short Term...Gales continue through much of the today as pres
gradient holds, but begins to slacken this afternoon. Expect
some moderate freezing spray this morning, and the again this
evening. Winds gradually diminish tonight, but will likely need
SCA overnight, with sub-SCA conds on Saturday.

Long Term... Another storm will cross the waters on Saturday
night with rain and snow showers. Cold northwesterly flow will
move in behind the system on Sunday with Gales possible. High
pressure builds in for the start of next week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Freezing Spray Advisory until 6 AM EST Saturday for ANZ150>154.
     Gale Warning until 6 PM EST this evening for ANZ150>154.

&&

$$

NEAR TERM...Hanes
SHORT TERM...Cempa
LONG TERM...Curtis



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