Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 251518

Area Forecast Discussion
National Weather Service Gray ME
1118 AM EDT Mon Sep 25 2017

High pressure will hold over the region today through Tuesday
night with temperatures remaining well above normal. A cold
front will approach from the west on Wednesday and will cross
the region Wednesday night. Expect a cooler and drier air mass
for the rest of the week while Hurricane Maria passes by well to
the southeast.


1100 Am Update...
Quick update to adjust temp/td/sky and RH grids. Morning valley
fog has pretty much lifted across the region with some cu
development occurring over the higher terrain in the mountains.
Looking for a mostly sunny afternoon with temps once again
soaring to near record levels. A developing sea breeze will
knock temps back into the upper 70s to lower 80s in coastal
areas. May see a sprinkle or shower in the mountains but these
should be light and widely scattered.

Prev Disc...
Have updated the grids based on current conditions. Areas of
dense fog continue to expand in western and northern NH as well
as portions of the western mountains of Maine. Have raised a
dense fog advisory good until 9 am. Otherwise, just a few
minor modifications to the morning forecast.

Prev Disc...
Patchy dense fog expected early this morning. Visibilities
locally near a quarter of a mile in fog, but not widespread at
this time. Nevertheless, will highlight with a Special Weather
Statement for the morning commute.

A large ridge of high pressure will remain entrenched over the
region today. H8 temperatures near +17C, sunshine and
relatively good mixing is expected after the morning fog
dissipates. This will allow for another very warm day with
readings in the 80s in just about all sections except for the
Midcoast region of Maine as winds become onshore near the coast
in the afternoon.

Moisture will be on the increase today with surface dew points
approaching 70 in some areas. This will make it feel even more
uncomfortable especially for so late in the season with heat
indices climbing into the lower 90s over portions of southern
New Hampshire.

Sufficient instability and differential heating to possibly
trigger a stray shower or isolated thunderstorm near and over
the higher terrain today. This is supported by this morning`s
mesoscale models. Any convection will likely remain over the
higher terrain as wind fields remain very light to spread the
shower activity off the hilltops.


Patchy fog once again tonight with visibilities lowering once
again. High pressure will remain in control as a warm front
remains just north of our region.

By Tuesday, expect a repeat performance from Monday. However,
temperatures may not be quite as warm as additional cloud cover
will drift over the region from an approaching cold front. There
may be a slight chance of a shower late in the day over far
northern areas as a cold front approaches from the northwest.


The large ridge which has brought sustained warmth to New
England for quite some time will get chipped away at by several
progressive troughs this week. The first passes by well to the
north on Monday, but in its wake it shoves a cold front
southward into northern Maine Tuesday night before stalling.
This could be the focus for a shower or two Tuesday night and
Wednesday, but otherwise expect the heat and humidity to
continue across the area. A southerly low level wind will keep
temperatures down a bit across Maine, but humidity remains high.

The next trough moves through the lower Saint Lawrence Valley
Wednesday into Wednesday night, sending a stronger front
southeastward into New England Wednesday night. This will be an
air mass changer for our region, with the heat and humidity
being swept off to the northeast while cooler and drier air push
in from the Canadian prairies. There will be some showers and
thunderstorms along the front as it moves toward our area
Wednesday night, but the best forcing for precipitation will be
sliding off to the northeast, so the best chance of rain will be
in the far northwest while coastal locations stand a good chance
of remaining dry. Once the front moves offshore it will begin
interacting with Hurricane Maria which will have drifted
northward to a position south and east of Cape Cod. Expect Maria
to be pulled quickly to the east and stay far enough south to
avoid any impacts in our area. Meanwhile, the cooler, drier air
will bring temperatures back to near normal levels by Friday and

Another trough swings through New England on Saturday and could
provide another chance of showers as it does so. But this trough
will be filling as it moves through and does not have a good
moisture connection, so precipitation chances will be rather
meager. It will, however, send a reinforcing shot of cool, dry
air into the region, with high pressure building in for Sunday
and Monday. Expect some good radiational cooling conditions at
night as high pressure sits over our area for a couple of
nights. Although a few spots managed to reach the freezing mark
way back on September 2nd, this could be the first freeze of
the season for other protected valley locations in the north.
This is about two weeks later than normal.


Short Term...VFR conditions today through Tuesday with high
pressure overhead. Patchy fog expected once again tonight over
most of the inland valleys.

Long Term...A flow off the water on Wednesday could bring in
some lower ceilings and visibility late Wednesday into Wednesday
night ahead of a cold front. This front will produce some
showers and a few thunderstorms in northern areas. Expect VFR
conditions to return on Thursday.


Short Term...Winds and seas will remain below SCA thresholds as
high pressure remains over the region.

Long Term...Although winds remain light over the waters, some
larger swells from the tropics may begin arriving Wednesday into
Thursday. A cold front will cross the waters early Thursday.




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