Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 161535 AAC

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
1135 AM EDT Wed Aug 16 2017

High pressure will continue to build into New England through
Thursday bringing dry conditions and seasonable temperatures.  On
Friday...a warm front associated with low pressure over the Great
Lakes will lift through the region followed by a cold front Friday
night.  These features will bring the threat of showers throughout
the region.  High pressure will build back into the region this
weekend with warming temperatures.


1132 AM Update...Boosted late morning temperatures particularly
along the coast based on observations...with a small increase in
cloud cover also necessary based on visible satellite imagery.
Much drier air is arriving /note quick drop in dewpoint at
Rangeley to 45 last hour/ with should help scour out remaining
clouds. Expect high temperatures to occur a bit early today
along the coast as better cool advection is now arriving and
will help slow the rapid rise we/ve seen in the downslope regime
late this morning. No other significant changes at this time.

920 AM Update...Quiet weather across the forecast area this
morning as high pressure centered north of the western Great
Lakes builds south and east towards the region with deep layer
subsidence overhead. Have updated near term temperatures to
match observations...where values are increasing more rapidly
than inherited forecast. 12Z GYX RAOB shows plenty of room for
drying and will lower dewpoint some in line with near term
mesoscale guidance...with dewpoints falling back into the 40s
/see similar values already showing up north of the
international border/. Otherwise...only very minor changes to
the forecast.

Original discussion below...
Overnight shower activity has fallen apart as the weak cold
front pushes into our area. With moist dewpoints in the 50s
expect fog to continue to form through dawn, with some dense fog
in the favored valley locations.

Today will see valley fog dissipate after sunrise. Increasing
northwesterly flow will bring drier air into the region during
the day. The pressure gradient will be just strong enough to
keep the seabreeze at bay and a few gusts to around 20kts are
possible in the coastal plain this afternoon.


Overnight high pressure builds over the region. Clear and dry
conditions will allow for good radiational cooling as the
atmosphere decouples. Widespread overnight lows in the 40s will
be the result. With dewpoints preventing the temperatures from
falling further, expect patchy fog in the valleys by morning.

Thursday will once again be sunny as high pressure remains
overhead. The upper low will remain to our northeast once again
keeping steady northwesterly flow across the region. Highs will
be near 80 south to 70 north.


Surface ridging will be in place to start the period across Nrn
New England. Aloft...the ridge axis is not forecast to cross the
region until at least midday Fri. So I think precip will have a
tough time moving in/developing until that as shifted to our E.
On the boundary of the WAA aloft and departing ridge...there may
be a band of showers that moves thru. More likely the narrow
warm sector will develop into more of an occlusion Fri night
with a more strongly forced band of showers and embedded
thunder. Models forecast some sharp drying aloft behind rainfall should come to a quick end from W to E into
early Sat. The main cold front will not cross the area until
later in the the threat of more isolated convective
precip will remain in the forecast until then.

Main cold pool swings thru aloft on it could be a day
of destructive sunshine where insolation leads to development of
more clouds. Lingering moisture in the cyclonic flow over the
terrain should also keep the mtns in the clouds with an isolated
shower or two.

Early next week high pressure will build to the S of the region.
At this time it looks like it will reach far enough N to keep
any frontal boundaries N of the forecast area. That high will
gradually drift Ewd thru the week...and by midweek SW return
flow is expected over the area as the next trof and frontal
boundary approach the region from the W.


Short Term...Overnight valley fog will result in IFR to LIFR
conditions through dawn today and again tonight. Otherwise VFR
will prevail as high pressure moves over head.

Long Term...As warm front lifts towards the area and flow
becomes onshore...conditions will deteriorate to MVFR or lower
across the area. Conditions near the coast will need to be some coastal fog/stratus is possible. At this time
it looks like front will be delayed enough that stratus will
have a smaller window to move into coastal Nrn New England. Cold
front will sweep across the forecast area Sat...and local IFR
conditions are possible in SHRA/TSRA. High pressure will build
in Sun with a return to VFR conditions.


Short Term...
While the high pressure overhead will keep locally
generated hazards to a minimum Hurricane Gert passing off shore
will have an effect on the waters in the form of long period
swell. Waves of around 5ft with a 12 second period are expected
to propagate from Gert as it passes 500 miles south east of the
Gulf of Maine. These waves will impact the more south facing
aspects of the coast from the midcoast through downeast. A High
surf advisory has been issued for the area from tonight through
late Thursday for Knox, Lincoln, and Sagadahoc counties,
including the offshore islands. A small craft advisory for
hazardous seas is also in effect for the adjacent waters during
this time period. Within Penobscot bay and Waldo county, as well
as further south within Casco bay and Cumberland county, the
sheltering effect of the islands and bays, combined with the
more east facing aspect will keep surf heights lower.

Long Term...As swell from Hurricane Gert diminishes a persistent
onshore flow will develop in response to a warm front lifting
across the waters. Seas may build above 5 ft again on the outer
waters...especially by Sat. Other than this window...winds and
seas are expected to remain below SCA thresholds.


ME...High Surf Advisory from 8 PM this evening to 8 PM EDT Thursday
     for MEZ025>027.
MARINE...Small Craft Advisory for hazardous seas from 8 PM this evening
     to 8 PM EDT Thursday for ANZ150-152.


NEAR TERM...Arnott/Curtis
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