Area Forecast Discussion
Issued by NWS Portland, ME

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229
FXUS61 KGYX 221310
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
910 AM EDT Tue Aug 22 2017

.SYNOPSIS...
High pressure retreats well offshore today. A strong cold front
will move across the region tonight and early Wednesday
accompanied by showers and thunderstorms. High pressure and
drier air follows the front Wednesday night through Friday.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...

905 AM...Minor ESTF update to reflect the current mesonet in
near term grids.


Prev disc...
650 am Update: Skies mostly clear early this morning with patchy
fog along the CT River Valley that will burn off in the next few
hours. Input latest mesonet data with no forecast changes needed
at this time.

Previous Discussion:
Some patchy early morning Valley fog along the Ct River
otherwise a mostly sunny start to the day. Considerable moisture
advection with very high PW`s and increasing shear will result
in rapid destabilization of the atmosphere during the afternoon.
This will result in strong to possibly severe thunderstorms to
develop first across NH and then spread east into Maine by mid
to late afternoon. Temps will be very warm with highs in the mid
to upper 80s. Pooling dewpoints reaching near 70 will make it
feel very muggy.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
The cold front and upper trof press east tonight allowing the
strong thunderstorms to continue in advance through most of the
evening before slowly weakening later at night and becoming
more widely scattered. The cold front moves off the coast
Wednesday morning allowing for cooler, drier air, and clearing
in its wake during Wed as high pressure builds in from the
west.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
The system that will bring rain to us today and Wednesday will
be its way out on Thursday. The parent surface circulation will
be well north in Quebec while the cold front which sweeps
through Wednesday morning will be well offshore. Aloft a deep
trough will continue to spin bringing occasional clouds and
isolated showers to the mountains...mainly in the heat of the
day each afternoon. However, for the most part large sprawling
high pressure which has been dominating the central states will
move into and strengthen over New England. This along with drier
air will suppress any further activity despite the persistent
troughing aloft. The exception to this may be a back door cold
front which could spark off a few showers on Sunday.

Temperatures will generally be close to normal values /mid 60s
north to mid 70s south/ for highs. Overnight lows should drop
into the 40s and 50s most nights under partial to complete
clearing and light winds.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
Short term...Patchy early morning fog in the CT River Valley
otherwise VFR this morning. Conditions lowering to MVFR and
locally IFR in developing afternoon and evening thunderstorms.
Some of the storms will be strong with gusty winds and possible
hail. The thunderstorms will weaken later in the evening but
scattered showers with MVFR conditions will continue until the
passage of the cold front by Wednesday morning. Conditions will
improve to VFR behind the FROPA Wednesday.

Long Term...Some patchy fog is possible early Thursday
morning...especially where it has rained. Also some mountain
valleys may radiate to the dew point each morning Friday and
Saturday.

&&

.MARINE...
Short Term...Winds and seas will increase later today and
tonight as the south to southwest flow increases ahead of the
approaching cold front. SCA conditions will develop this
afternoon and continue through tonight and into Wednesday.
The cold front will cross the waters Wednesday allowing a
gradually wind shift to the west helping knock down the seas by
later in the day.

Long Term...Winds and seas will remain calm for the remainder of
the week.

&&

.TIDES/COASTAL FLOODING...
We`re in the period of high astronomical tides for the month of
August. The remaining high tide of potential concern
(referencing Portland Harbor where flood stage is 12.0 ft MLLW)
is:

1231 AM Wednesday. 11.1 ft MLLW

Tonight`s high tide (1231 AM Wednesday) could see some
splashover and minor beach erosion as onshore flow and seas
increase ahead of an approaching cold front.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory from 8 PM this evening to 8 AM EDT
     Wednesday for ANZ151-153.
     Small Craft Advisory from 3 PM this afternoon to 8 AM EDT
     Wednesday for ANZ150-152-154.

&&

$$

ES



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