Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 171645
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1145 AM EST Fri Nov 17 2017

.SYNOPSIS...
Northwesterly flow in the wake of a departing low pressure
system will bring some gusty winds today. High pressure will
build in overnight before sliding offshore on Saturday. A warm
front will lift northward on Saturday night with a mix of rain
showers south and rain/snow in the north. A cold front will
cross the region on Sunday bringing gusty winds and accumulating
snow to the mountains. High pressure builds in for the start of
next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

1145 AM...Minor ESTF update to reflect current low cloud
coverage as well as the latest mesonet in near term grids.

Prev Disc...
900 AM...For this ESTF update I adjusted cloud cover to reflect
low cloud trends on GOES imagery and to ingest the current
mesonet into near term grids. Morning KGYX raob supports gusty
northwest winds today with a few gusts to near 40 mph possible
with daytime mixing and momentum transport.

Prev disc...
7am update... Just some minor updates to the cloud clover and
pops. Snow showers continue along the spine of the mountains.

Prev...Low pressure over New Brunswick brings a strong pressure
gradient and northwesterly flow to the region this morning.
Winds are gusting to 20 - 25kts across the region currently and
expected to increase to 25 - 30kts through the morning hours.
Forecast soundings show a well mixed lower layer and a few gusts
to 40kt are possible. After noon the low will move off to the
northeast allowing the winds to subside through the evening. The
northwesterly flow is also generating upslope showers and
clouds. Expect far northern New Hampshire to pick up a dusting
of snow this morning with clouds lingering through the day.
Downwind of the mountains downslope drying and clearing has
already eroded the low clouds in most places and skies will
become sunny for most of the day.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Overnight a brief ridge of high pressure builds in ahead of the
next system. With calming winds, especially towards the high
center north and west of the region have gone on the lower end
for temperatures overnight with the north dropping to around
10F.

Saturday will see the high pressure pass through as southerly
flow and increased cloud cover moves in ahead of the next
system. The warm front will begin to push northwards with
temperatures climbing above freezing throughout the area and as
warm as 50F on the Massachusetts border. Precipitation will just
begin to approach the region from the west late Saturday
afternoon.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Focus of the extended is on the strong low pressure forecast to
NEwd thru the St. Lawrence Valley this weekend. S/wv trof
tracking across the central CONUS is forecast to amplify and
become negatively tilted as it crosses the Northeast. Strong low
pressure will develop ahead of the s/wv and drive a cold front
thru the forecast area.

17.00z NAM remains an outlier...by developing low pressure and
tracking it thru Srn New England. This is a much colder
scenario...and has little support except from a small handful of
17.00z GEFS and EPS members. That being said...12z raob network
should begin to sample the s/wv in question across the West
Coast...and this should provide some higher confidence in model
forecasts. In the meantime I will lean towards the GEFS and EPS
solutions...with strong consensus track thru the St. Lawrence.

That will initially bring precip to the area along the warm
front. Some of this may fall with the column cold enough for
snow...especially at elevation. Gradually a non-diurnal temp
trend will warm the boundary layer up for mostly rain. With
strong forcing for ascent and PWAT values pushing 1 inch...250
percent of normal...a sharp line of heavy rainfall is possible
along the cold front. Winds will be gusty ahead of the
line...but I am expecting enough of an inversion to keep the
bulk of that aloft. Post-front however mixing depths increase
sharply and CAA will help mix down stronger winds aloft.
Forecast soundings show the potential for fairly widespread 40
kt gusts in the Wly flow behind the front. Those gusty winds
look to continue right into Mon...though gradually diminishing
over time. Some wind headlines look likely for Sun...possibly
into Sun night.

The pattern behind this system looks generally zonal. This will
bring fast moving s/wv trofs and mainly upslope snow showers.
Temps will remain near to below normal.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Short Term... Low ceilings have eroded this morning as downslope
winds result in drying conditions through the coastal plain. VFR
with wind gusts to 25 - 30 kts expected today, with MVFR in SHSN
in the mountains early this am. Winds will diminish late today
with high pressure building in and VFR holding through Saturday.

Long Term...Conditions...if not already IFR...will deteriorate
quickly Sat night. RA will overspread the region...with some SN
across the far interior. Some LLWS is probable...especially Sat
night across the Srn half of the forecast area. Cold front comes
thru Sun afternoon...with winds shifting Wly and precip becoming
more showery. Conditions will quickly improve to VFR S of the
mtns...with lingering MVFR at HIE in upslope flow. Surface wind
gusts 35 to 40 kts possible at all terminals Sun. Gusty winds
will continue into Sun night and Mon. Generally VFR S of the
mtns...with Wly flow continuing upslope clouds at HIE.

&&

.MARINE...
Short Term...Northwesterly flow and cold air advection in the
wake of the departing storm will see winds increase through the
morning with gusts to gale force and a gale warning remains in
effect for today. Winds will decrease as high pressure moves
into the area overnight. Saturday will see a warming trend as
southerly flow ahead of the next system moves into the area.

Long Term...Sly flow increases thru Sat night...though forecast
soundings suggest wind gusts may stay just below gale force.
Gale force winds are most likely when CAA begins and wind
direction shifts to Wly. Outside of the bays winds may even gust
to near storm force for a time Sun into Sun evening. Winds will
stay gusty thru Sun night. With offshore flow seas will build to
10 to 15 ft outside of the bays.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Gale Warning until 8 PM EST this evening for ANZ150>154.

&&

$$

ES


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