Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 200914 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
514 AM EDT Sun Aug 20 2017

.SYNOPSIS...
High pressure will build south of the region today through
Monday before sliding to the east on Tuesday. A cold front will
move in from the west Tuesday night and will cross the region on
Wednesday. High pressure will build in behind the front
Wednesday night through Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
510 AM Update: Going forecast in good shape with some minor
adjustments to placement of weak sprinkles/light showers moving
east ahead of mid level shortwave. However...regional water
vapor imagery shows deep layer drying arriving from the
west...which will bring remaining showers to an end in the next
1-2 hours. Fog is also showing some signs of thinning during the
past hour along the midcoast...with some new patches showing
back up over the CT valley. Rapid improvement is expected around
daybreak and shortly thereafter. Temperatures remain mild and
bumped up near term temps 1-2 F based upon these observations.

Original discussion below...
High Impact Weather Potential: Patchy dense fog RKD-AUG-LEW
region through daybreak.

Current Pattern: Cold front has now exited the forecast area with
shortwave trough axis overhead and also about ready to exit east.
Blended total precipitable water product shows a pocket of drier air
centered over the Great Lakes...poised to move east into New England
as heights build behind departing trough.  Surface high pressure is
centered over WV/VA and is also gradually pulling east.  The pattern
portends a quiet near term forecast with primary forecast concerns
centered around current fog/low stratus and when it will break up.

Through Daybreak: Tracking a band of sprinkles and light
showers that are now moving into southwestern New Hampshire.
These have weakened substantially over the past few hours...but
will continue to lift north and east ahead of mid level
shortwave through daybreak. By daybreak...any remaining shower
activity will become increasingly confined to the upslope areas
in the mountains. Further east...have seen occasional dense fog
at LEB-AUG-RKD and have issued an SPS for this as improvement
will arrive from the west over the next few hours...and
certainly no later than daybreak. Temperatures generally
remaining in the 60s for overnight lows.

Today: For a few hours this morning...expect some lower clouds
and perhaps shower/sprinkle activity in the upslope areas of
northern NH before better moisture lifts north and east.
Otherwise...expect any remaining shallow moisture over eastern
areas to quickly mix out today...with skies turning partly to
mostly sunny /a few Cu all areas and some mid clouds closer to
the international border/ under developing moderate /10 mph gust
to 20 mph/ northwesterly winds. Otherwise...T8s have fallen
2-3C from yesterday to around 11-12C...but with more morning sun
expect most locations to see high temperatures close to or just
shy of what was observed today...with 70s from the mountains
north and lower/middle 80s over the coastal plain into the
foothills.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
High Impact Weather Potential: None.

Pattern Summary: Brisk zonal flow aloft is expected through the
short term forecast period between mid level low moving into the
Hudson Bay region...with climatological high over the southeastern
states.  Surface high pressure east of the Mid Atlantic reaches our
longitude during the day Monday with ridge axis north of this
feature pretty much dominating the surface pattern through the short
term forecast period.  Driest air through the column will settle
overhead tonight...gradually shifting east on Monday with values
near climatological norms through the period.

Tonight:  With high pressure centered just south of the
region...llevel gradient relaxes with decoupling expected all areas
under clear skies. Afternoon dewpoints suggest a decent place to
start for expected overnight lows...and expect a cooler night than
the past few with the drier airmass overhead.  Lows should reach the
50s for most areas...with southern NH and coastal ME likely
remaining at or just above 60.

Monday: Deep west southwest flow aloft with surface high pressure
gradually pulling off the US east coast with return flow
strengthening.  Nearest frontal boundary will be draped well north
and west of the forecast area...extending from central Quebec south
and west into the Great Lakes region.  While this won/t be close
enough to have any meaningful weather impacts...could see some high
cloudiness stream east from any ongoing convection.  This bit of
cirrus and perhaps a few daytime Cu will be all that will impact
viewing of the eclipse over the forecast area.  A warm day is in
store with T8s around +15C.  While the eclipse will likely temper
temperatures for 1-2 hours...do not expect that this will have much
of an influence on the actual highs...which may be pushed an hour
later...but still reach the 80s most locations...with MHT-ASH-SFM
corridor potentially hitting 90.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
A warm and humid southwest flow will continue Tuesday in advance
of an upper trof and associated cold front. By late Tuesday
showers and thunderstorms will spread across much of NH and
western ME. Tue night into Wed showers and thunderstorms are
expected as the upper trof moves across the region. By Wed
afternoon the upper trof and cold front moves off the coast
allowing clearing to take place in the afternoon. High pressure
builds across the region Thu and into the weekend with near
seasonal temps and dry conditions.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
Short term /through Monday/...

Summary: High pressure will build south of the region through
Monday bringing improving flying conditions to the area.

Restrictions: LIFR fog/stratus is gradually eroding from the
west with RKD/AUG likely to improve to VFR around daybreak.
Otherwise...could see some IFR fog develop near LEB around
daybreak with upslope cloudiness bringing MVFR restrictions to
HIE through the morning. VFR this afternoon through Monday
outside of potential fog redevelopment tonight HIE/LEB and
potentially RKD.

Winds: Light and variable winds overnight will become northwesterly
and increase to 10g18kts for the day today before diminishing back
to calm tonight. Winds will become westerly 10-15kts for the day on
Monday.

LLWS:  LLWS is not expected through Monday.

Lightning: No thunderstorms are expected through Monday.

Long Term...
VFR Tuesday. Areas of MVFR/IFR conditions in showers and
thunderstorms late Tuesday into Wed. Becoming VFR for late
Wednesday through Friday.

&&

.MARINE...
Short Term /through Sunday Night/...
Westerly wind gusts may reach 20-25kts for a time Monday afternoon
in the outer waters...but in general winds and waves are expected to
remain below SCA levels through the short term forecast period.
Ongoing fog over the waters is expected to dissipate this
morning.

Long Term...
SCA`s may be needed late Tuesday into Wednesday over the outer waters.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$
SYNOPSIS...
NEAR TERM...Arnott
SHORT TERM...Arnott
LONG TERM...Marine
AVIATION...Arnott
MARINE...



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