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FXUS61 KGYX 251129
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
729 AM EDT Sat Mar 25 2017

.SYNOPSIS...
A cold front shifts south of the region today and stalls there,
producing some rain and snow over southern New Hampshire.
High pressure builds in tonight from the north and will shift
east on Sunday. A warm front will approach from the southwest on
Sunday and cross the region Sunday night, providing 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
the west for the end of the week.

&&

.NEAR TERM /TODAY/...
730AM UPDATE...
Have updated the forecast based on early morning temperatures.
Although the wind shift with the cold front has moved through
to southern New England, the cold air is really only being felt
across the state of Maine where temperatures have actually
fallen below freezing. Elsewhere temperatures have remained
above freezing tonight.

ORIGINAL DISCUSSION...
A cold front is sliding southward early this morning, and has
made its way to near the Massachusetts line already. This will
bring a light northerly wind today with some drier air.
Meanwhile, a mid level shortwave trough will squirt eastward
over the top of a sharp ridge over the eastern Great Lakes and
move through southern New England during the day today. This
will provide another round of precipitation, primarily to
southern New Hampshire. As precipitation arrives, once again
expect temperatures to cool and precipitation to quickly become
snow. Some light accumulation is possible, but temperatures are
expected to be near or above freezing which should prevent
significant accumulation. If all of the forecast QPF accumulates
as snowfall, then it is possible that up to 2 inches could
accumulate, but again we expect it to begin as rain and
temperatures to be near or above the critical melting point
which will limit accumulations to under an inch after the change
over. Further to the north and east across the eastern part of
the forecast area, temperatures will warm into the low to mid
40s this afternoon and stay dry.

&&

.SHORT TERM /TONIGHT AND SUNDAY/...
High pressure shifts over the area tonight which will allow
winds to go calm with good radiational cooling conditions. How
low we go will depend on the amount of low level moisture. It
looks like at least northern areas will have enough dry air in
place to allow temperatures to drop into the single digits,
while southern New Hampshire and coastal Maine may only drop
into the 20s.

As the high shifts east on Sunday it will set up an easterly low
level flow across New England. This type of flow promotes cold
air damming to the east of the mountains. With cold
temperatures expected to start the morning, the damming should
keep the temperature from warming all that much across eastern
New Hampshire and coastal/interior Maine. By Sunday afternoon,
the onshore low level flow may bring enough moisture to produce
some light drizzle or freezing drizzle, mainly over eastern New
Hampshire and southwest Maine. The temperature is expected to be
fairly close to the critical 32 degree mark, so will need to be
alert for the potential for light icing to occur. Models would
like to warm temperatures above freezing Sunday afternoon, but
with a cold air dammed flow that may not happen. Have lowered
forecast temperatures below model guidance to account for this.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
At 500 mb, coldest core of air sits north of Labrador through
the weekend, with troughing shifting eastward across far
northern Maine tonight and Sunday. Several weak waves will move
through zonal flow behind this system from Sunday through
Wednesday, before a larger trough closes off east of the
Maritimes at then end of the week. The good news is that the
coldest air retreats poleward, and the bad news is we have to
deal with several bouts of precip for the early to mid week.

Sunday night and Monday is the trickiest part of the forecast
as a warm front aloft lifts through the region in response to a
weak low tracking out of the Great Lakes and up the St Lawrence
Valley. The question is to what extent the cold air damming
will keep cold air locked in at the surface since surface ridge
tends to be located more to our east than northeast in classic
damming situations. Flow may end up more onshore, especially
along the coast, as surface gradient is more southerly, but
initially weak. This may keep coastal areas above freezing
Sunday night, but it will be close. Inland areas will probably
be just below freezing, and with nearly isothermal profiles, may
see a little of everything when it comes to precip. Still,
precip amounts should be relatively light, and given a
combination of snow and freezing rain, perhaps even some sleet,
will likely make for a messy commute Monday morning. On Monday,
the southerly gradient tightens and expect to see temps rise
above freezing most everywhere, with rain likely through the
day.

By Monday night, very weak low wants to form over the Gulf of
Maine and this will likely kill any damming but will also
weaken the flow a bit. Could see some freezing or frozen light
precip or drizzle develop over inland areas again, although
coastal areas should remain above freezing. By Tuesday, any
sense of damming will be gone and temperatures aloft rise to
around 5C, so should surface temps rise well above freezing
everywhere, although clouds and showers are likely to linger as
low level flow remains weak and cold front hangs back. The
first cold front shifts through late Tuesday and may produce
a round of showers with a secondary cold front moving through
Wednesday looking mostly dry.

Temps behind the system drop to near -10 C at 850, but only for
a day. Thursday looks fair but still a few degrees below
normal. Next system approaches Friday, with the best chance of
chance of any precip not until Friday night.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Short Term...Cold front which dropped through early this morning
has improved conditions to VFR for most areas and cleared out
the brief fog. Another round of light rain and snow is expected
again today, primarily over southern New Hampshire. Conditions
could become IFR at times in the snowfall with MVFR ceilings
possible as far north as Portland. Precipitation ends tonight
with a return to VFR conditions.

Long Term...Flight restrictions look to be in the forecast
Sunday through Tuesday night, and will probably be IFR or lower
Sunday night through Monday night. Expect some improvement to
MVFR Tuesday and Tuesday night. VFR expected by Wednesday. Some
light FZRA expected Sunday night into Monday morning,
especially away from the coast.

&&

.MARINE...
Short Term...Light winds are expected over the waters as high
pressure crosses the region through Sunday.

Long Term...Weak low pressure developing over the waters Monday
should keep winds below SCA levels, but as the low shifts east
Tue-Wed, will see NW flow pick up and may need SCA Tue night and
Wed.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$

LONG TERM...Cempa
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