Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 200241 AAC
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
941 PM EST Thu Jan 19 2017

.SYNOPSIS...
The area will remain generally under the influence of high
pressure...with fair weather and warmer than normal temperatures.
A weak front will try and push into the area during the
weekend...but is unlikely to bring us much more than very light
showers or flurries. On Sunday a cold front drops through the
area...bringing more cooler temperatures than precipitation. This
front will set up the battle ground between rain and mixed
precipitation or snow as the next weather maker moves up the
coast on Monday into Tuesday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
940 PM Update...
Low level stratus as well as fog is now affecting the region with
moisture trapped under an inversion evident on this evening`s
KGYX 00Z sounding. NW winds have recently begun to pick up as
surface trough moves away and northwest flow aloft increases in
response to blossoming baroclinic leaf structure over the Ohio
River Valley.

Temperatures...skies...and winds were adjusted through the
overnight hours for latest near term guidance and current trends.
Temperature readings are still on the warm side having only fell
a few degrees so far from today`s highs.


725 PM Update...
Stratus is hanging tough under a low level inversion tonight with
temperatures/dew points nearly stable or even creeping up. As a
result have adjusted the nocturnal trend. Will be likely settling
on temperatures a few degrees warmer than the previously
forecasted lows which were in the teens and low 20s. We may not
see much clearing with light and variable winds through the night
as high pressure drifts in from the west.


Previous discussion...
Upper trof is crossing the area this afternoon...with s/wv
ridging expected to build in quickly in its wake. Surface ridge
axis will settle overhead around 12z. That points towards
radiational cooling tonight...but dewpoints are also rising this
afternoon rather than mixing out. Still I feel this is mainly
shallow in nature...and we should trend colder than guidance
tonight. But the low level moisture does lead me to think some
patchy fog is likely across the area.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Another mild January day on Friday...with temps reaching towards
40 near the coast. High pressure will be drifting E and allowing
return flow to set up. Clouds should gradually increase later in
the day...as upper ridge axis approaches.

Friday night is an interesting forecast...as a s/wv trof lifts
out of the OH River Valley and shears out into the ridge. Low
levels are forecast to remain at or near saturation...while upper
levels remain dry within the ridging. SW flow with the s/wv
produces some modest isentropic upglide...especially into SWrn
zones before fizzling out. This low level lift combined with
unsaturated mid and upper levels points towards a drizzle or
freezing drizzle scenario. Forcing for ascent will be on the
weaker side so it could amount to nothing...or even flurries. I
opted to put flurries or patchy drizzle/freezing drizzle in the
forecast...though PoP is low due to lack of confidence.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Upper level ridging over the area on Saturday gives way to a
trough dropping south from Canada and another trough moving in
from the southwest. Not a lot of cold air associated with this as
blocking upper ridge remains to our north, limiting the cold air
available. However, there will be just enough cold air to make the
forecast interesting. Main period of concern is from Monday into
Tuesday as the trough coming in from the southwest is likely to
develop a coastal low and spread precipitation into our area.

As the northern stream trough drops south through the Canadian
maritimes it will send a cold front southward through northern New
England Saturday night into Sunday. Expect cooler temperatures
along with an easterly low level flow which should set up cold air
damming conditions as time goes on. By Sunday night, temperatures
across the area should fall freezing.

Meanwhile, upper level low pressure tracking across the southern
portion of the country will reach the Southeast coastline by
Monday morning, with surface low pressure developing over the near
Norfolk, VA. This low will expand and grow as it tracks northeast
toward Cape Cod Monday into Monday night, spreading moisture
northward into our area. Temperatures associated with this system
will be somewhat tricky considering the cold low developing to our
south and the blocking ridge to our north. Models are coming into
better agreement that there will be enough cold air aloft for at
least a period of snow across the area, with the potential for
warmer air aloft to change precipitation over to sleet and
freezing rain. Confidence is fairly high that temperatures in the
low levels will remain cold enough to be concerned about
frozen/freezing precipitation right through the day on Tuesday, as
low level easterly flow promotes cold air damming at the surface.
At this point it is becoming a question of snow vs freezing rain
more than a question of a mix to rain. Our blend of models is
still struggling with the cold air damming, so temperatures were
lowered especially on Tuesday to account for this. With a
northerly flow expected across the area, it is unlikely that
temperatures warm above the low to maybe mid 30s.

Light snow or drizzle could begin as early as Sunday as the
onshore easterly flow begins. But the best precipitation chances
begin arriving Sunday night into Monday when the best forcing for
ascent north of the low moves into our area. This should provide a
few inches of snowfall as it moves from south to north through the
area. Meanwhile, the surface low will track northeast toward Cape
Cod Monday night, providing another chance for more substantial
precipitation. It is during this time period that more mixed
precipitation is possible with warm air aloft possibly moving as
far north as the Canadian border, changing precipitation to
freezing rain or freezing drizzle. It is also possible that the
developing low will be strong enough to keep cold air pulled in
closer to the low center, keeping precipitation as snow. This is a
source of significant uncertainty at this point, so the going
forecast will mention just about every precipitation type. The low
will move out Tuesday into Tuesday night, bringing precipitation
to an end.

Expect warmer temperatures again behind the system as there is a
general lack of cold air available. Temperatures Wednesday and
Thursday of next week are likely to be 5 to 10 degrees above
normal. Another wave moving through Wednesday night could provide
another chance of precipitation, mainly rain or snow depending on
surface temperatures at the time.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Short Term...MVFR CIGs remain on the NW side of the mountains.
High pressure builds in overnight...and CIGs will gradually
scatter out. HIE will remain MVFR the longest...with LEB
scattering out this evening. With clearing and low level
moisture...I do think BR or FG is possible overnight with IFR or
lower conditions...but I am not confident in location to put in
the TAFs. Currents signs point to interior NH being more likely
than western ME however. Very late Friday night some flurries or
drizzle/freezing drizzle is possible across SW NH...possibly
affecting LEB...CON...and MHT. Confidence is low however.

Long Term...Could see some MVFR ceilings on Saturday as a
dissipating wave moves into the area. Generally VFR afterward with
a front dropping down from the south early on Sunday. An easterly
low level flow could pull in some moisture for some MVFR or IFR
ceilings later on Sunday, with MVFR/IFR conditions lasting through
midweek as a storm system tracks up the coast. Expect a wintry mix
of precipitation types ranging from snow to sleet to freezing rain
from Monday into Tuesday.

&&

.MARINE...
Short Term...Winds remain below SCA thresholds...though seas
outside the bays remain at or above 5 ft. Model guidance favors
another small increase in seas tonight after the passage of the
upper trof...and so I have extended the SCA for hazardous seas
thru 12z.

Long Term...Light winds are expected through Sunday when an
easterly low level flow begins. This flow will strengthen, likely
reaching advisory levels Sunday night. As low pressure tracks up
the coast, expect winds to reach into Gale force range out of the
east or northeast on Monday, lasting until the low moves by
Tuesday. There is a low chance that storm force gusts could occur.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory for hazardous seas until 7 AM EST Friday
     for ANZ150-152-154.

&&

$$
SYNOPSIS...
NEAR TERM...Hanes
SHORT TERM...Legro
LONG TERM...Kimble
AVIATION...Kimble/Legro
MARINE...Kimble/Legro



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