Area Forecast Discussion
Issued by NWS Portland, ME

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579
FXUS61 KGYX 261611
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1211 PM EDT Sun Mar 26 2017

.SYNOPSIS...
High pressure crosses the region today. A warm front will
approach from the southwest on Sunday before a weak wave of low
pressure forms and passes through the Gulf of Maine Monday. This
will provide a round of mixed wintry precipitation Sunday night
into Monday. Low pressure moves north of the region on Tuesday
and drags a cold front through on Wednesday. High pressure will
build in from Canada for the end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
UPDATE...
Have updated the grids based on current conditions. Cold and dry
air in place during the midday hours after Canadian high
pressure built into the region during the overnight hours. Full
sunshine however will allow temperatures to climb into the mid
to upper 30s this afternoon. Have adjusted max temps upwards by
a few degrees based on current trends. Dew point values will
remain very low going into our next precip event tonight as a
northerly wind continues over the forecast area for a few more
hours.

PREV DISC...
High pressure over western Maine this morning is
allowing some cold and very dry air to filter down into the
area. Dewpoints in eastern Maine are solidly subzero early this
morning with temperatures in the teens and single digits even
into western Maine and northern New Hampshire. As high pressure
moves east today, expect an easterly pressure gradient to
develop which will promote the damming of this cold, dry air up
against the mountains of New Hampshire and western Maine. After
a cold start, temperatures will rebound a bit due to a fair
amount of sun early in the day. But increasing clouds and
continued cold air damming should keep temperatures from rising
out of the low to mid 30s for most areas. The GFS model is the
most aggressive at developing a period of drizzle/freezing
drizzle within the easterly upslope area of New Hampshire this
afternoon, but this seems a little overdone and is not supported
by most models. The GFS is also the coldest model perhaps in
part due to the clouds and light precipitation it develops.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Wave of low pressure ejecting out of the middle Mississippi
Valley today will move toward our area tonight. Expect an
initial round of light precipitation, probably snow, to move
through the area during the evening as warm advection begins
aloft. More persistent precipitation will begin arriving later
in the night. At this point, temperatures aloft will be warming
to above freezing for at least part of the area, while low level
temperatures remain near or below freezing. This will cause
precipitation type to change to freezing rain over southern and
western parts of the area. Expect ice accumulations from just a
light glaze to as much as a quarter of an inch by morning across
central, southern, and western New Hampshire.

Models are now indicating the development of a secondary surface
low over southern New England on Monday, tracking east into the
Gulf of Maine. This development will have the effect of keeping
the cold air locked in place across western Maine and eastern
New Hampshire. In fact, this cold air could be deep enough for
some sleet across interior western Maine which will limit total
ice accumulations there a bit. As the low and parent trough move
east on Monday, expect precipitation to come to an end from west
to east during the afternoon or evening, possibly lingering a
little longer in the western Maine mountains.

A mix of Winter Weather Advisories and Freezing Rain Advisories
have been issued for the area to draw attention to the expected
wintry conditions. The freezing rain will be the primary hazard
here considering its impact on travel. The Advisories were
structured so that Winter Weather Advisories were used for areas
which are expected to get an inch or more of sleet and snow in
addition to the freezing rain, while areas expected to get less
than an inch of snow and sleet were given a Freezing Rain
Advisory to highlight the more significant hazard.

There is still a lot of uncertainty with regard to
precipitation type. It is late March after all, and this is not
a climatologically favored time for freezing rain, especially
during the day. However, it`s also not that common to see such a
dry/cold air mass either. The model forecast easterly flow will
serve to pile up this cold air against the North-South mountain
ranges of New Hampshire, locking the cold air in place and
allowing it to drain southward. The development of a secondary
surface low tracking to the south of the area serves to increase
confidence in the low level cold air damming, but also raises
the possibility that precipitation may fall as more snow/sleet
as deeper cold air is pulled in to the north of the low. This is
a particularly challenging forecast and it will be worth it for
users to monitor the forecast for updates and changes as the
event begins.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
500 mb flow trends from weakly to more moderately amplified
during the extended range, and will be highly dependent on
stream of closed lows moving to the Western and Southwestern
United States before lifting NE toward the Great Lakes and
Northeast. These will ultimately determine how amplified flow
becomes and timing of troughing and ridging. Blocking over
Europe should allow for deepening troughs to our east. The one
positive is that this will allow the coldest air to shift back
toward the pole, and while we may not see too much in above
normal temps, they will shift more toward normal thru the
period.

Monday night remains tricky, mainly in the northeast where
temps may remain below freezing through the night with some
freezing rain expected, although mounts should be light. Could
also see some snow or sleet mix in at times, given some colder
air moving in aloft as the low intensifies a little over the
Gulf of Maine. Elsewhere precip may see a break late Monday
night as warm sector aloft moves in, but onshore flow may allow
some drizzle to persist on the coastal plain.

Tuesday will see another weak low shift south of the region, further
offshore than than the previous low. It will drag a cold front
across the region, which could produce another round of showers
Tuesday afternoon/evening. Could see some spots in southern NH
break out into the warm sector before this front comes thru, in
which case they may see temps 50 or higher. Once the front goes
thru Tuesday night, will see colder air aloft and some snow
showers will be possible. The front will wipe out the occlusion
and marine layer, so Wednesday will be warmer than Tuesday in
many spots with highs in the 40s to low 50s.

Thursday will be a little cooler than Wednesday, but coldest
air aloft will have moved through already. Temps warm up a
little bit more on Friday, with next system approaching Friday
night and bringing a chance for precip Friday night and Saturday.
May start as some wet snow in some places, but should be rain
during the day Saturday.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
Short Term...Conditions start VFR today with very light winds.
But expect increasing clouds from southwest to northeast as the
day goes on, and by evening ceilings will begin lowering to
MVFR. Light snow changing to sleet and freezing rain from
southwest to northeast is expected tonight into the day Monday
with IFR conditions expected. There is still a great amount of
uncertainty on precipitation type, but freezing rain is possible
at all terminals for at least some time, possibly lingering
into the afternoon on Monday at Augusta. Eventually temperatures
will warm above freezing and cause precipitation to change to
rain.

Long Term...IFR or lower Monday night and Tuesday with
RA/FG/DZ. May see some improvement to MVFR During the day
Tuesday at KMHT/KCON. Some improvement to MVFR everywhere
Tuesday night with VFR Wednesday-Thursday. May see NW wind
gusts to 25 kt at times on Wednesday.

&&

.MARINE...
Short Term...Light winds and low seas are expected over the Gulf
of Maine as high pressure crosses the waters today. A southeast
flow will develop ahead of a developing surface low on Monday,
and this flow could bring some higher seas and possibly some
wind gusts to 25 KT late Monday.

Long Term...Seas could reach 5-6 feet in swell from coastal lows
Monday night and Tuesday. Winds will reach SCA levels in NW
flow behind a cold front Wednesday, perhaps lasting into
Thursday.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory from 8 PM this evening to 5 PM EDT
     Monday for MEZ007>009-012>014-018>022.
     Winter Weather Advisory from 8 PM this evening to 10 AM EDT
     Monday for MEZ023>028.
NH...Winter Weather Advisory from 8 PM this evening to 5 PM EDT
     Monday for NHZ001>004-006-009-010.
     Freezing Rain Advisory from 8 PM this evening to 10 AM EDT
     Monday for NHZ005-007-008-011>015.
MARINE...None.

&&

$$
NEAR TERM...Cannon
SHORT TERM...Cannon
LONG TERM...Schwibs



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