Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 010233
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1033 PM EDT Fri Sep 30 2016

.SYNOPSIS...
An upper level low pressure will slowly meander across the
Northeast through the weekend. Showers will move into New
Hampshire and eventually western Maine this evening and overnight
as the low drifts closer. The low moves overhead on Sunday and
cross the region on Monday brining more scattered showers. High
pressure will build in for the middle of next week.

&&

.NEAR TERM /TONIGHT/...
1030PM UPDATE...
Showers have broken up a bit as they have moved north. 00Z upper
air observation shows extremely dry air just above the surface
which explains why it`s been so difficult to get this rain to make
it in here. There have now been several reports from automated
sites in southern New Hampshire (and now even Sanford, Maine)
indicating rain is falling, though visibility restrictions are
just now starting to sneak into southern New Hampshire hinting
that the rain is getting a little more substantial. With this
update there was not much change to precipitation chances as prior
update seems to convey the message well. Overnight low
temperatures were reduced a bit, though, as evaporational cooling
could help lower temperatures in some areas, while further to the
north and east high level cloud cover will not offer as much
protection from the radiational cooling as shown by temperatures
already falling more quickly than expected.

530PM UPDATE...
Band of showers has finally drifted north into far southern New
Hampshire. Still have not seen an observation of rain reaching the
ground in New Hampshire, but across the border in Massachusetts
there are a few automated sites reporting 10SM rain. Even though
the rain is quite light and may not amount to measurable
precipitation very quickly, when people step outside they are
likely saying, "it`s raining." Therefore will increase
precipitation chances in southern New Hampshire for the next
several hours as the rain will likely get a little bit heavier and
more widespread over that region. Still should have a tough time
making it further north into Central New Hampshire and most of
Maine.

ORIGINAL DISCUSSION...
Strong high pressure remains branched across southern Canada this
afternoon. This is holding dry air in place across much of the
forecast area...allowing clouds to repeatedly break up as they
move N. This has also been holding precip back thru the day.
Showers and areas of rain will steadily move N into southern NH
this evening...reaching parts of western ME near midnight. Given
the dry antecedent air...I do not expect precip to be all that
heavy. Precip will be most likely for southern NH...and highest
amounts should stay under a half inch.

&&

.SHORT TERM /TONIGHT AND SATURDAY/...
Early Saturday the remaining band of showers will continue
crossing the northern parts of the forecast area as forcing lifts
N. Southerly flow aloft will continue the warm advection...and as
a result I do not want to eliminate the chance for showers as warm
air rides over the low level colder air. With the cool...dry high
to the N and precip falling into the column...we should see a fair
cold air damming signature on Saturday. I undercut the high temp
guidance...especially across the favored middle part of the
forecast area. A secondary s/wv trof moves N later Saturday...and
could increase coverage of showers a bit. I have PoP likely along
the coast...but keep it chance or lower across the interior. Upper
lows are notoriously tricky for model guidance...and typically see
more dry weather than not...so I do not want to overdo it with
likely or higher PoP. So I will play it as two time periods of
increased chances...early Saturday and late Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
High Impact Weather: Low

Overview: An upper level closed low will slowly move out of the
midwest and cross New England early next week as it weakens
brining some rain to start the week. High pressure will build in
through the middle of the week.

Sunday: Sunday the last of the weak ridging will decay as the
upper low moves eastward out of the great lakes. Skies will be
cloudy as upper level moisture moves in. Along the coast...the
flow continues to have a slight onshore component. The moisture
doesn`t look quite deep enough to support widespread drizzle, but
expect higher pops and some low clouds hugging the immediate
coastline.

Monday: Monday the upper level low will cross the region. This
will bring scattered showers, initially starting in the southwest
and gradually spreading out across the region. While most areas
will see some rain through the day the amounts won`t be much. Cold
temperatures aloft will help to enhance the shower activity, and a
few bits of graupel mixing in are possible.

Tuesday- Wednesday: High pressure will move into the region for
Tuesday and Wednesday. Once again northeast flow will set up
parallel to the coast which should keep most of the region
sunny.... All but the midcoast peninsulas and islands where the
slight onshore component will lead to some low clouds over the
Gulf of Maine. Temperatures will remain seasonable with highs in
the 60s and lows in the 40s.

Thursday and beyond: The end of week is a very low confidence
forecast at this point. At 500mb we have the ridge which built in
at the start of the week starting to progress eastward while in
the western CONUS a trough strengthens. Model solutions differ
quite a bit in how quickly they allow that upper level
progression. In all longer term scenarios persistence and
blocking tend to win out over any fast progression... so I would
tend to favor the slower ECMWF solution over the GFS. Nevertheless
both ensembles have a wide variety of solutions. This upper level
pattern will be watched closely over the next several days as how
it sets up will determine what happens to Hurricane Matthew after
it turns northward next week and begins to interact with the mid
latitudes. This entire scenario is still 6+ days away and really
beyond the time in which any confidence can be assigned to
specific predictions.

&&

.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
Short Term...A BKN MVFR deck remains more or less stationary
across southern NH. As moisture continues N this evening this
deck should gradually fill in and lift N. I expect widespread MVFR
tonight S of the mountains. SHRA and some areas of -RA will move
S to N across the southern half of the forecast area tonight.
MHT...PSM...CON...LEB and PWM are most likely to see precip before
dawn. Some local IFR conditions are possible near the coast
tonight. SHRA become a little more scattered Saturday...but MVFR
conditions should linger for most terminals into the day.

Long Term...
Low ceilings and IFR conditions possible for RKD PWM and PSM
Sunday in onshore flow. Monday showers will bring periods of MVFR
to the entire region. VFR returns for Tuesday.

&&

.MARINE...
Short Term...Seas remain above 5 ft S of Port Clyde. SCA will
remain in effect thru tonight as NE flow continues this swell.
Seas may diminish slightly late tonight...only to build again
tomorrow as low pressure moves closer. Will keep the SCA going for
winds and seas...as gusts will be near 25 kts. It is possible
Saturday afternoon that winds and seas increase enough to bring
all zones into a SCA.

Long Term...Northeast flow will continue through Sunday but remain
below sca. Winds and seas will be calm through mid week as high
pressure builds in.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ152-154.

&&

$$

NEAR TERM UPDATE...Kimble
SHORT TERM...Legro
LONG TERM...Curtis
AVIATION...Curtis/Legro
MARINE...Curtis/Legro



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