Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 271337 AAB

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
937 AM EDT SAT AUG 27 2016

High pressure moves into northern New England today with dry and
warm weather expected. The high pressure will move east into the
Atlantic on Sunday with a cool onshore breeze over coastal areas.
A cold front arriving from the west will bring a chance of showers
and thunderstorms Sunday into Sunday night with high pressure
building in behind the front through midweek.


940 am Update...
Only minor changes to the forecast this morning. Have issued the
fire weather products. Fog has mixed out for the most part with a
few spots remaining south of Lebanon but these will be gone soon.
Temperatures will warm quickly today in a drier airmass.

630 AM UPDATE...
Have updated the forecast to tie into latest temperatures early
this morning. Fog in the New Hampshire valleys will be a little
slow to burn off especially in the southern half of the
Connecticut River Valley.

High pressure over the area today will bring light winds and less
humid conditions. Temperatures will still be well above normal,
generally in the 80s. A sea breeze can be expected along the
coast, cooling temperatures a bit there.


Light winds should allow for good radiational cooling conditions
tonight, with most areas falling into the 50s. Expect valley fog
to be more widespread by morning. Could also see some fog
developing over the ocean spreading into coastal Maine by morning
as well.

With the high off to the east on Sunday, synoptic flow will be
out of the southeast. This will bring a cooling ocean influence to
much of Maine while interior New Hampshire warms into the mid 80s
again. A couple of minor disturbances within the largely zonal
flow aloft ahead of a sharp shortwave trough could help to
trigger some showers and thunderstorms mainly over northern areas
during the afternoon. Low level moisture return is somewhat
lacking so overall instability is rather limited so severe
thunderstorms are not very likely even given moderate and
increasing shear.


The extended begins with a cold front set to cross the region.
Model consensus on timing is delaying the frontal passage until
after dark. Showers look likely across much of the the
s/wv trof maintains strength and heights fall overnight. We will
be missing surface based instability...but I will add thunder to
the forecast even for the nighttime hours. Forecast soundings from
even the GFS have some elevated instability...and a scenario like
the NAM forecast soundings would make thunder even more likely. On
that model...a strengthening SW low level jet will help to force
convection aloft despite relatively stable surface layer.

Beyond early Mon...high pressure will build in for the first half
of the work week. Flow is fairly zonal aloft and should help to
move systems along quickly. The next s/wv trof approaches
midweek...and it is this one that helps to set the stage for Ern
CONUS troffing into the weekend. Ensemble guidance continues to
favor lower than normal heights and cooler than normal mid level
temps. GEFS PWAT forecasts are also on the dry side...which would
make sense for offshore...continental flow on the backside of the
upper low.


Short Term...Early morning valley fog may take a little longer
than normal to burn off due to the lack of wind flow, but
conditions will eventually become VFR by late morning at all
locations. Expect a sea breeze along the coast during the
afternoon. Fog will once again be a possibility tonight,
especially at Whitefield and Lebanon. There is a lower chance of
valley fog formation at Concord and Manchester, while marine
stratus and fog could impact Rockland and Portland by Sunday morning.

Long Term...A cold front will approach the region Sun night. SHRA
and embedded TSRA look to cross the area during the overnight.
Areas of MVFR conditions will be possible as the front
crosses...with local IFR or lower in any heavier convection. More
widespread IFR conditions may be possible if coastal fog/stratus
can develop ahead of the front. Otherwise high pressure builds in
behind the front...and VFR conditions will prevail into midweek.


Short Term...High pressure shifts into the Gulf of Maine today and
tonight. Could see some fog developing over the ocean tonight,
pushing toward the coast Sunday morning.

Long Term...SW flow ahead of an approaching front Sun night will
give way to Wly flow behind it. Persistent offshore winds may
build seas outside of the bays to around 5 ft by midweek.





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