Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 150801
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
301 AM EST Wed Nov 15 2017

.SYNOPSIS...
High pressure builds in from the north today and continues the
cool weather. Low pressure is expected to develop over southern
New England early Thursday and move into the Gulf of Maine late
Thursday and Thursday night. Coastal rain and some accumulating
interior snows are expected. Cold high pressure builds in again
for Friday before the next storm system arrives this weekend
with another mixed bag of precipitation. High pressure then
builds in early next week.

&&

.NEAR TERM /THROUGH TODAY/...
Surface high pressure will be centered over NH and ME today.
However, moisture trapped beneath a subsidence inversion has
allowed for a stubborn deck of clouds early this morning. As
drying continues, the clouds are expected to thin out with
mostly sunny skies expected for most locations by mid morning.
However, it may take til around midday for this to happen in
some areas, especially in southern NH. Otherwise, light winds
are expected with highs mainly in the 40s.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
A rapidly advancing short wave trough will approach from the
west tonight. As a result clouds are expected to increase from
west to east, especially after midnight. Moisture and forcing
for ascent will further increase toward dawn a likely result in
light precipitation developing across western zones. At this
time, it looks to be a light mixed bag with some snow, sleet,
and a few pockets of freezing rain possible in the CT river
valley. Will have to watch this for possible minor travel
inconveniences for the Thursday morning commute.

Precipitation will continue to overspread the area early
Thursday morning. As southerly winds increase, most areas will
see rain but the mountains should hang on to enough cold air to
allow for a mix for much of the day. Accumulating snow is likely
there, especially at higher elevations.

Things get interesting Thursday afternoon. As has been
advertised in deterministic models and ensembles for the last
few days, secondary low pressure still looks to develop to our
south and move into the Gulf of Maine by later Thursday
afternoon. The main question has been will this low develop fast
enough and close enough to the coast to allow for a period of
heavy precipitation Thursday afternoon and evening. At this
time, the consensus of deterministic and ensemble solutions is
yes. However, there remains some spread - with a few late
bloomer solutions still on the table which would keep heaviest
precip offshore.

At this time will continue to take a consensus approach which
brings a period of moderate to possibly heavy precipitation to
mainly coastal and central zones Thursday afternoon and evening
due to rapidly developing frontogenetical forcing. The main
issue then becomes precipitation type. As the forcing for ascent
increases, cold air should be drawn in and/or manufactured.
This should result in any mixture of precipitation changing to
snow in the mountains. The big question mark is the area roughly
from interior Cumberland County ME northeastward to the KLEW-
KAUG corridor on north/northeastward into the foothills where
the column below 850 mb will be well above freezing to start. As
long as strong frontogenetical forcing occurs, the column
should cool enough to at least end the precipitation as some
snow. This will have to be watched closely, but for now will
forecast an inch or two along the I-95 corridor north of Gray,
with several inches in the mountains. Mesoscale details will
become clearer over the next 24 hours - but until then it is
hard to know how forcing will exactly unfold Thurs afternoon and
evening. Stay tuned.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
A fairly high amplitude and progressive pattern develops over
the next week driving several systems through northern New
England.

Friday will see the upper level low departing to the northeast
leaving the region under northwesterly flow. Have increased PoP
as well as QPF and snow for far northern New Hampshire as the
flow direction strongly favors snow showers hanging on
throughout the day up there. Elsewhere to the south and east
expect skies to become clear.

Friday night look for brief ridging to build into the region
with clear skies ahead of the next system.

Looking ahead to the weekend the overall forecast confidence
decreases. An upper level trough will swing east through the
CONUS with the attendant surface low tracking up the St.
Lawrence valley and pushing a warm front and then cold front
through Northern New England.

 While a storm is likely, the timing as well as precipitation
type is still uncertain. Timing continues to push back with
precipitation arriving later in the day on Saturday. This is
most likely the result of the blocking pattern currently
present in the northern hemispheric flow which will need to
break down in order for this storm to progress into our region.
The trend towards a later start time may ultimately result in
precipitation not starting until much later in the afternoon.

The second portion of the uncertainty in this system is the
precipitation type. Along the warm front, some overrunning
aloft may push enough warm air over the surface cold from Friday
night for light icing. As the timing of the precipitation
becomes later however, the window of time below freezing for
freezing rain also decreases. With quite light qpf amounts and
high uncertainty have opted not to include mention of Freezing
rain at this time but this will need to be monitored.

With the low occluding to our northwest the time in the warm
sector will be brief as a cold front sweeps across the region
early Sunday morning. This will rapidly change over the northern
portion of the area to snow as the precipitation comes to an
end. Similar to the forecast for Friday morning have left
upslope snow shower in the mountains lingering into Monday.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Short Term...VFR conditions are expected today and through much
of tonight. Later tonight into Thursday morning, precipitation
is expected overspread the region from west to east resulting in
MVFR conditions turning to IFR for the bulk of Thursday. IFR
conditions are then expected for Thursday night.


Long Term... MVFR showers will linger in the mountains on Friday
while elsewhere VFR continues. Another storm system will
approach the region for the weekend. On Saturday the warm front
lifts northward with MVFR ceilings moving in. Expect periods of
IFR in snow through the north overnight Saturday into Sunday
morning before conditions return to VFR area wide by Sunday
afternoon.


&&

.MARINE...
Short Term...Have issued a gale watch for all waters starting
Thursday night as low pressure passes through the Gulf of Maine.
W/NW winds gusting to gale force are expected in the wake of the
system into Friday.

Long Term...Gales will subside on Friday evening as the low
departs the region. A warm front will cross the area on Saturday
bringing scattered showers. Another cold front will cross the
waters on Sunday and winds behind the front will once again gust
to near Gale by Sunday afternoon.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Gale Watch from late Thursday night through Friday evening for
     ANZ150>154.

&&

$$

NEAR TERM...Ekster
SHORT TERM...Ekster
LONG TERM...Curtis



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