Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 222303
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
703 PM EDT Sun Oct 22 2017

.SYNOPSIS...
High pressure will hold over the maritimes tonight through Monday. A
slow moving cold front will approach from the west Monday night and
Tuesday and will slowly cross the region Wednesday through Thursday.
A shallow ridge of high pressure will build over the region on
Friday and will shift offshore on Saturday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
7 pm Update: Weak sfc meso-low sitting just off the coast
allowing a light moist northeast flow producing an area of low
stratus along and off the coast. This area of low clouds should
linger the rest of the night. Otherwise updated mesonet data and
only minor near term tweaks needed for the rest of the evening.

Previous Discussion:
High pressure sliding into the Maritimes has set up a bit of a
backdoor cold front across the area...with PWM at 57 this
hour...and EEN 82. Surface ridging still remains in control of
the region...so after dark we should see big drops in temps. Dew
points again are higher than previous days...so only an isolated
reading of upper 30s is expected in the coldest of valleys.
Otherwise mainly 40s tonight. The increased moisture should
allow for a little more ground fog...though dense fog is a
little more uncertain. Model guidance is bullish on widespread
marine fog tonight. The tendency is for models to rush this in
on return flow...which is just beginning to develop. However
there is a band of MVFR clouds just off the Seacoast and SWrn ME
coast. The warm temps inland is helping to erode the leading
edge of this...so I have at least some concern that at nightfall
this may surge inland. I have trended this way in the sky
forecast...but I have not gone heavy on the fog given the
moisture is fairly shallow in nature. That will be the forecast
challenge for tonight. Otherwise valley fog is expected farther
inland from coastal influences.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Another very warm late Oct day on tap for Mon. With mixing to
H9...we should see widespread upper 60s to lower 70s. With
deeper mixing in Sly flow this should bring some uniformity to
high temps.

Mon night deeper moisture arrives. With it I expect marine fog
and stratus to develop and move inland. With WAA ongoing above
the marine layer...some drizzle or an isolated shower is
possible. Temps should also remain more or less steady after
sunset. Overall I think Mon night the forecast area will remain
in the WAA in the warm sector...but steady precip will hold off
until later in the day. For that reason I backed off the likely
PoP that model guidance was spitting out.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Slow moving front will continue to inch toward the region on Tuesday.
Strong onshore flow will mainly produce areas of drizzle and
scattered showers during the day as main focus of heavier rain
remains across eastern New York and western New England. High temps
will generally range through the 60s.

Heavy rain will gradually shift into western New Hampshire Tuesday
night. Strong low low level jet will combine with tropical moisture
to produce 1 to 2 inches of rain across the western half of the
state by Wednesday morning with lighter amounts in eastern New
Hampshire and western Maine. Lows overnight will range from the mid
50s to lower 60s.

Heavy rain will gradually shift east on Wednesday affecting most of
the forecast area through the day. Looking for additional rainfall
amounts of 1 to 2 inches in eastern New Hampshire and western
Maine by the end of the day. With area rivers at record low
levels for this time of year not anticipating any flooding
problems but poorly drained areas and urban street flooding
could become an issue by late in the day.

Rain will continue Wednesday night as upper trough to the west of
the forecast area goes neg tilt slowing surface trough over central
Maine and wrapping considerable moisture back to the west. This
will result in another 1 to 2 inches across much of the
forecast area overnight and may result in problems on small
rivers and streams through out the forecast area. Lows overnight
will range from the mid 40s to lower 50s.

Focus of heavy rain will gradually shift into eastern Maine on
Thursday. Expect occasional showers through the day with some
minor additional accumulations possible...mainly in eastern
zones. Highs on Thursday will range from the mid 50s to lower
60s.

Upper trough will swing northeast through the region keeping showers
in the forecast through the 1st half of Thursday night.
Downsloping winds behind departing low and a shallow ridge of
high pressure building in from the west will bring clearing to
the region after midnight. Lows overnight will dip into the mid
30s to lower 40s.

Quiet weather returns to the forecast area on Friday as high pressure
builds south of New England. Highs on Friday will range from the mid
50s north to the lower 60s south. Fair weather will extend into
Saturday as another deep trough and slow moving cold front approaches
from the west.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Short Term...Tricky forecast this evening and overnight along
the coast. There is a band of MVFR CIGs in marine onshore flow
running from near PSM to PWM then off shore. Model forecasts
have this becoming widespread LIFR tonight. However model
guidance does tend to rush this...and guidance already suggests
this should be widespread LIFR CIGs at the moment. Keeping in
mind that moisture is still relatively shallow...30s dew points
around 1000 feet...and this is only the first night of return
flow I have not gone IFR or lower at coastal terminals. I did
however include some MVFR CIGs...as some convergence along the
coast could allow this band of clouds to persist. CT River
Valley should also see fog tonight...with LEB seeing LIFR
conditions after 08z most likely. With E flow...HIE may remain
mixed enough to avoid fog again. Mon will return to
VFR...followed by increasing moisture and clouds Mon night. More
widespread IFR marine fog/stratus is likely...along with
developing -RA or -DZ towards morning.

Long Term...
Widespread IFR/LIFR ceilings and MVFR vsby Tuesday through
Wednesday. MVFR/IFR ceilings Thursday...improving to VFR
Thursday night. VFR Friday.

&&

.MARINE...
Short Term...NE flow along the coast will stay below 25 kts this
evening before weakening and turning more onshore. Then winds
and seas will remain below SCA thresholds thru Mon. Mon night
increasing Sly flow will start to build seas towards 5 ft
late...leading into stronger winds Tue. Will also have to watch
for some marine fog/stratus tonight...but especially Mon night.
Shallow moisture should limit coverage and density...but deeper
moisture Mon night should allow for more widespread low
visibility.

Long Term...
Gales likely Tuesday through Tuesday night.

&&

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

&&

$$
NEAR TERM...Marine



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