Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 211255
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
855 AM EDT Mon Aug 21 2017

.SYNOPSIS...
High pressure will build to the south of the region through
tonight before sliding to the east on Tuesday. A cold front
will move across the region Tuesday night and early Wednesday.
High pressure and drier air follows the front Wednesday night
through Friday.

&&

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

855 AM...At 12z a ridge of high pressure was draped across New
England. Outside of a few high clouds...and a few fair weather
cumulus to develop in daytime heating...a mostly sunny day with
high temperatures mainly in the 80s. For this ESTF update...I
made minor adjustments to near term grids to reflect the current
mesonet.

Prev Disc...
7am Update: Quiet morning with only some high clouds spilling
into the region. Only fog this morning seems to be restricted
to the CT River Valley area and will burn off in the next hour
or so.

Previous Discussion:
Patchy early morning fog otherwise mostly sunny conditions
again today. Some high clouds may occasionally spill across the
upper ridge at times. Temperatures will be warm with highs in
the 80s across most areas.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH TUESDAY NIGHT/...
High pressure centered to our south will continue to dominate
conditions tonight with dry conditions but a slow rise in
dewpoints will be noted making for a muggy night as overnight
lows remain in the lower to mid 60s. Some patchy fog once again
expected after midnight and into Tuesday morning.

Tuesday will be a very warm and humid day with clouds on the
increase and scattered showers and thunderstorms developing from
west to east in the afternoon. Highs will be mostly in the mid
to upper 80s and supported by h85 +15C temps.

Tuesday night widespread showers and scattered thunderstorms
expected. Total qpf amounts should range mostly in the .25-65
inch range by Wed morning. Stayed close to RFCQPF guidance.
Models differ some on ending times with EURO slower and NAM/GFS
about 3-6 hour sooner.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
A deep but narrow upper low will stretch from the Northwest
Passages in Canada southward to the Mid Atlantic region. This
is part of a Rex block which will be in the process of mutating.
The easterly low will continue to dig into the Northeastern
states from the midweek period through the weekend with weak
energy aloft.

A cold front will be moving offshore Wednesday morning with
precipitation coming to an end from west to east. Should be some
patchy fog around during the morning hours. WPC`s QPF totals for
the next 7 days are less than a half inch everywhere except for
the NH and western ME mountains which may see up to an inch.
Most of this is attributed to this event. Over the mountains,
lingering clouds and a shower or two will continue Thursday
before drier air begins to filter in. We should be able to warm
up again under downsloping winds with 80s along the coast and
mid o upper 70s inland. The higher elevations should warm into
the 70s.

High pressure will be in control at the surface beginning
Thursday and for several days fostering drier and cooler
conditions for late this week into early next week. Highs will
drop from the 70s and 80s Wednesday to the 60s and 70s which is
more in line with normal values for this time of year.

Precipitable water values generally drop below 0.60" or less
than 50% of the climatological normal during this time so there
should be some nights when we will see ample radiational cooling
as the high shifts closer overhead. Overnight lows will drop
into the 40s and 50s with some chilly mornings in the higher
elevations. This will be the first taste of fall for many
places.

&&

.AVIATION /13Z MONDAY THROUGH FRIDAY/...
Short term /through Monday Night/...VFR...with sct MVFR and LCL
IFR btw 08 - 12z this morning in valley fog. LCL IFR conditions
again btw 06-12z Tue in valley fog. Late Tue and Tue night
conditions lowering to MVFR to IFR in developing showers and
scattered thunderstorms ahead of an approaching cold front.

Long Term...LIFR to MVFR conditions are forecast for all
terminals Wednesday as a cold front brings scattered showers to
the region with some heavier rain for the mountains. Showers may
linger for HIE and LEB through Thursday morning before drying
out along with the rest of the region. Some fog is possible
Thursday morning. Otherwise VFR for the remainder of the work
week. Westerly winds may initially be gusty on Wednesday before
diminishing under high pressure Thursday and Friday.

&&

.MARINE...
Short Term /through Monday Night/...Winds and seas are expected
to remain below small craft through early Tuesday as surface
high pressure builds to our south. By late Tue and Tue night an
increasing south to southwest flow ahead of the approaching cold
front will allow SCA conditions to develop.

Long Term...Seas will remain above small craft criteria through
Wednesday morning at least before diminishing. Winds should stay
below 25 kts.

&&

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

1140 PM Monday.... 11.2 ft MLLW
1231 AM Wednesday. 11.1 ft MLLW

The Tuesday night high tide (1231 AM Wednesday) could see some
splashover 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 Tuesday to 8 AM EDT Wednesday
     for ANZ151-153.
     Small Craft Advisory from 3 PM Tuesday to 8 AM EDT Wednesday
     for ANZ150-152-154.

&&

$$

ES


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