Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 191314

Area Forecast Discussion
National Weather Service Gray ME
914 AM EDT Sat Aug 19 2017

A slow moving cold front will approach the region
today...crossing the area this evening. High pressure will
build in from the west tonight through Monday and will slide
offshore 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



910 AM...Slow improvement today from west to east as somewhat
drier air begins to work in and the low cloud gradually burns
off. For this ESTF update...I made minor adjustments to reflect
current mesonet as well as satellite trends.

Prev disc...
621 AM Update: Minor changes to the forecast this hour to follow
morning temperature/dewpoint observations as well as some light
shower activity weakening over western Maine. Patchy fog
continues...but has been highly variable in space and time.
Expect a few more changes once we get a few more visible
satellite images to get a better feel for cloud cover above the
low stratus and fog.

Original discussion below...
High Impact Weather Potential: Moderate rip current risk along
area beaches. Otherwise...minimal.

Current Pattern: Current surface map places low pressure over
western Quebec with cold front trailing this feature south through
upstate New York and through the Mid Atlantic.  East of this cold
front...and warm front is draped from west to east across
southern New England...responsible for /by far/ the most
significant widespread rainfall in well over a month. A weak
wave of low pressure formed along this front overnight and has
helped push the front back south with northerly flow having
overspread much of southern Maine and New Hampshire.
Still...southwesterly flow aloft /ahead of Great Lakes
shortwave/ over this cool dome continues to spawn a few showers.
Southwesterly flow will continue across the forecast area
today...with aforementioned warm front moving/mixing northward
and forecast concerns centered around shower potential ahead of
approaching cold front.

Through Daybreak: Generally quiet through daybreak with just a
few showers given flow over llevel cool dome. Otherwise...cloudy
skies and areas of fog given ample llevel moisture after
yesterday/s rainfall.

Today: Deep moisture plume moves offshore this morning with
PWATs falling back below 1.25" by late morning and through the
afternoon. Thus...despite upstream cold front and strengthening
mid level flow...instability will be lacking with very poor
lapse rates in the 850-500 mb layer. Near term high resolution
deterministic and ensemble guidance suggest the best threat of
any pop up shower activity will be over northern areas...closest
to the coolest temperatures aloft associated with upstream
shortwave. Can/t rule out a rumble of thunder...but overall
it/s looking like most locations will remain dry today. Given
the drying airmass...we should see an increasing amount of
sunshine as the day progresses...and with T8s around +15C there
is ample room for temperatures to climb well into the 80s over
southern NH...with highs tempered a bit further east where
morning clouds/fog will be more persistent. Employed MOS for the
highs which is a bit above the guidance consensus...with some
upper 80s possible in the MHT/ASH corridor.


High Impact Weather Potential: None.

Pattern Summary: Upstream shortwave pulls through the region tonight
associated with surface cold front.  Drier air and significant
height rises arrive for the day Sunday as a surface ridge of high
pressure builds south of New England.

Tonight: Surface cold front should pass through the region during
the evening hours...but upstream shortwave trough axis will not
arrive until closer to 06z...with low level cyclonic flow persisting
through the overnight. Thus...could see a few evening showers
over the foothills and mountains before any shower coverage
becomes increasingly confined to the upslope regime in the
mountains. Clouds will persist in this area...with partly cloudy
skies to the south and east. With only modest dry advection
overnight...lows will again be mild...generally in the upper 50s
north to lower/mid 60s south.

Sunday: Aforementioned significant height rises spell deep-layer
subsidence as PWATs fall back to values around 1 inch...right around
normal for this time of year.  Could see a few residual showers in
the mountains during the early morning...but otherwise a drier and
somewhat cooler day will be in store with ample sun and T8s around
+12C  should allow highs into the 80s south of the mountains
/given some downslope assistance/...with 70s elsewhere.


A ridge of high pressure will be centered south of the area
Monday and will move offshore Tuesday as a cold front slowly
approaches from the west. This will lead to increasing
temperatures and humidity for Monday and Tuesday. High temps
Tuesday will mainly range from near 80 in the mountains to near
90 in southeastern New Hampshire and extreme southwestern Maine.
Along with the warmer temps and higher humidity, the threat of
showers and possible thunderstorms will be on the increase
Tuesday afternoon through Wednesday as a cold front approaches
and crosses the region. Showers could linger Wednesday night.

A Canadian air mass with much cooler and drier air follows moves
across the region behind the front for Thursday and Friday as
surface high pressure builds into the region. With the colder
air moving in aloft and an upper level trough developing over
the area Thursday and Friday, an afternoon instability shower
can`t be ruled out, especially in mountain areas, but most areas
will remain dry.


Short Term...
Summary: Gradual clearing is expected today ahead of an
approaching cold front that will move through the forecast area
this evening with high pressure and drier air arriving for

Restrictions: Variable conditions at the moment with many sites
LIFR/IFR in low stratus and some fog. There will be gradual
improvement from west to east through the morning hours...with a
return to VFR expected. Generally VFR for the afternoon with
possible isolated to scattered restrictions in showers /and
possible a thunderstorm/ LEB-HIE-AUG. This evening...expect
VLIFR-LIFR fog/stratus to set in at AUG/RKD with additional fog
likely HIE/LEB after 08Z Sunday. All sites will become VFR on

Winds: Light winds at the moment will generally become
southwest 5 to 10kts for the day today before diminishing to
light and variable tonight. For the day on Sunday expect winds
to shift northwesterly and increase to 10g16kts.

LLWS: No LLWS expected through Sunday.

Lightning: Very low chance of a thunderstorm this afternoon
HIE/LEB/AUG. No thunderstorms expected tonight through Sunday.

Long Term...VFR conditions for Monday into Tuesday. MVFR to IFR
conditions likely Tuesday night and Wednesday in showers and
possible thunderstorms.


Short Term...SCAs /updated to be for hazardous seas only as of
624 am/ continue through this evening over the outer waters
with winds now beginning to diminish...but lingering 4-6 foot
waves continuing through the day today. Waves diminish this
evening...with no flags expected tonight through Sunday.

Long Term...No flags into early Tuesday. An increasing
southerly flow will increase winds and seas late Tuesday with
SCA conditions possible by Tuesday night and into Wednesday.


MARINE...Small Craft Advisory for hazardous seas until 5 PM EDT this
     afternoon for ANZ150-152-154.


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