Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 161525
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1025 AM EST Mon Jan 16 2017

.SYNOPSIS...
High pressure brings fair weather into Tuesday morning. Low
pressure moves out of the region Tuesday night into Wednesday
night and will bring snow, with some mixed precipitation, to the
area. High pressure builds in for the end of the week, with above
normal temperatures.

&&

.NEAR TERM /UNTIL 5 PM THIS AFTERNOON/...

1020 AM...At 15z a 1034 millibar high was centered vicinity of the
DELMARVA. GOES imagery showed a few clouds over northern and
eastern sections of the forecast associated with warm front. for
this ESTF update...I adjusted near term grids to reflect satellite
trends as well as the 15z mesonet. I added slight chance pops for
light snow showers over far northern Maine mountains for this
afternoon. Nil other changes.

Prev Disc...
640 AM...Mostly some minor adjustments to T/Td/Sky to bring the
forecast into line with current obs. MAy see a few more clouds
work thru the far north this morning, but otherwise should be
mainly sunny with temps running a little above normal.

Previously...Sfc high moves offshore today as weak area of low
pressure passes well to the north of the CWA, this will likely
produce a round of clouds this afternoon and evening across the
nrn zones, and maybe a few flurries or SHSN. Highs today will be
several degrees warmer than Sunday, ranging from around 30 in the
north, to the mid to upper 30s in the south.

&&

.SHORT TERM /5 PM THIS AFTERNOON THROUGH 6 PM TUESDAY/...
High pressure will build back in briefly late tonight into
Tuesday. Southern areas should be mainly clear, with mountain
clouds thinning out after midnight. There will be some potential
for rad cooling, with light winds, but overall temps will be
warmer than previous nights, ranging from 15-20 in the north, to
the mid 20s in the south and along the coast. Tuesday will start
off mainly sunny, but clouds will overspread the region from SW-
NE in the afternoon ahead of the next system. Could see light rain
or snow break out prior to the evening across southern NH, but
bulk of precip will hold off until Tue evening.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
High impact weather potential: low confidence of warning level
snowfall Tuesday night into Wednesday

Overview: The extended forecast is a relatively low confidence
forecast due to the uncertain strength and timing of the many
shortwaves which will move through the region over the week. To
start off the week a strong high amplitude ridge is built into the
North Atlantic east of Iceland. This is providing substantial
blocking to the hemispheric flow and keeping the coldest of polar
air trapped just to our north over Labrador and Baffin island.
Across North America we have a split flow with a weak low aloft
over the southwestern united states and a weak ridge built on top
of it through the northern Rockies. This puts the northeastern
CONUS at the junction of two possible storm paths. The first more
northern stream is colder and relatively dry consisting of
shortwaves originating over Alaska and the Yukon diving southwards
across Canada and approaching across northern Ontario. The second
path is coming out of Texas and moving up towards the great lakes.
This flow is generally weaker but much more juicy due to its
ability to tap into moisture from the Gulf of mexico. The two
storm tracks is what makes this forecast period so uncertain as
the timing of both tracks will impact our weather as the two waves
may either reinforce each other or cancel each other out as they
approach.

/00Z Wednesday to 00Z Thursday/ Our first time period of concern
is Tuesday night into Wednesday. Here the southern stream is our
primary player with a storm system currently generating widespread
freezing rain across the central plains tracks north and east into
the great lakes. Precipitation will begin moving into western NH
around 00Z on Wednesday and rapidly overspread the region. By 12Z
Wednesday a secondary low begins to develop off the Atlantic
coast, shifting the precipitation off shore and brining it to an
end by 00Z Thursday. Of course all is not quite so straight
forward. The main concern here the temperature profile both aloft
and at the surface which will determine p-type.

 Most of the uncertainty in this system is due to the strength of
the departing high which will be over the maritimes as evidenced by
the ensemble sensitivity. The GFS represents a warmer solution
with a weaker high while the Euro is the colder option with a
stronger high and the Canadian bridging the difference. My
preference is towards the stronger high and colder solution due to
the fact that the flow is blocked which generally results in a
longer time to move any cold air out. Stronger high pressure will
provide colder surface temperatures but also help to force the
bulk of the heaviest precipitation amounts to the southern portion
of the CWA. This is a double edged sword as the warm air could
still infiltrate aloft to the south allowing the southern
portions of the CWA /where highest qpf is expected/ to switch
over to sleet or wetter snow. The line between snow and rain is
very close to the NH/MA border with much of southern NH within 1-2
degrees of switching over.

In addition to the temperature profiles there are several other
mesoscale effects that may play a significant role in this storm.
Provided surface temperatures remain cold enough for snow, there
is the potential for a brief period of heavy snow overnight due
to excellent updrafts in the snow growth zone. Further a inverted
trough may serve to focus the precipitation extending from the
newly forming coastal low off Cape Cod northwestward towards
Burlington VT across southern NH which could also increase
precipitation totals in this region. Finally the high pressure to
the north and low forming over Cape Cod sets up a nice scenario
for a coastal front as well as upslope snow for southern Maine.
All of this combines to yield the highest snow potentials from
Lewiston through Fryeburg in Maine and into the Lakes Region of
NH and Concord and as far south as the higher terrain of
Hillsborough and Eastern Cheshire counties. This region has the
potential to see 5+" of snow putting it right on the cusp of a
winter storm watch. With all the uncertainty in thermal profiles,
and the precipitation still being almost 2 days out have opted not
to issue a watch on this forecast package.

/Thursday - Friday/ As we move into Wednesday night and Thursday
the northern stream pushes another disturbance through the region,
this time passing to our north. Here the Canadian is the strongest
putting widespread precipitation across much of Maine while the
other options are drier and weaker. Again with the blocking have
leaned towards a later arrival for this system which would result
in just a few inches of upslope snow showers in the mountains for
Thursday morning, however the potential for the timing to change
and and earlier arrival would result in a reinforcement of the
existing system for the midcoast and downeast region.

/Friday - weekend/ Friday high pressure builds back into the
region leaving us in above normal temperatures. The next potential
storm develops to our south off delmarva on Saturday however this
is very uncertain at this point.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
Short Term...VFR conditions through most of Tuesday. Could see
some late day MVFR-IFR at KMHT/KCON/KLEB is SN or RA Tue.

Long Term...
Tue night - Wed... Snow moving into all terminals with mixing
SN/PL/RA for MHT PSM. PWM and RKD will see RA/SN. Widespread IFR
on Tuesday night will increase to MVFR by mid day Wednesday.

HIE will hold onto MVFR SHSN through through Thursday.

&&

.MARINE...
Short Term...HAve issued SCA for outer waters this after and this
evening as SW flow surges briefly to around 25 kts and pushes
seas up to 5 ft.

Long Term...SCA conditions to borderline Gales will result from
Tuesday nights easterly flow across the waters.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until midnight EST tonight for ANZ150-152-
     154.

&&

$$
ES



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