Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 230109 AAC

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
909 PM EDT Sat Apr 22 2017

High pressure and drier air will finally build into the region
on Sunday. A cold front will drop south into northern New
England Sunday night into Monday and stall. Low pressure will
slowly move up the Eastern Seaboard Tuesday and Wednesday with
drizzle and periods of rain. A cold front will approach from the
west Thursday into Friday.


910 PM Update...
Minor changes to the forecast for clouds moving through and some
mixing ensuing on the northern edge of the stratiform clouds.
Still expecting a dreary overnight period with lingering
drizzle, fog, and stratus.

625 PM Update...
Areas of light drizzle and fog continue across the area this
evening. An isolated shower may be possible over the higher
terrain. Adjusted drizzle to just cover the coastal locations
and lightened the intensity as few stations are reporting it. At
the moment ceilings are increasing, but dew point depressions
will decrease after dark, and BUFKIT soundings show many areas
with a mixture of lower stratus and fog once again overnight.
Adjusted QPF accordingly. No other changes at this time other
than hourly temperatures/dew points.

Previous discussion...
A short wave trough will cross the region tonight. The result
will be better mixing and drying as it passes, which will aid in
getting rid of the murky low clouds and drizzle. This will
first occur in the west, then finally make it to the coastal
plain by dawn. We will have to watch for locally dense fog
overnight however. This may occur on the coastal plain as
stratus builds down. In addition, some dense fog may also form
over the interior if skies go clear for several hours.
Otherwise, not much in the way of measurable precipitation is
expected overnight.


High pressure builds across the region on Sunday and this will
result in a much nicer day than what we have seen the last few
days. During the afternoon, southwest flow will develop which
will help boost temperatures into the 60s in many places under
plentiful sunshine.

A cold front will cross the region from the NW Sunday night.
This front will be moisture starved and not bring anything except a
period of clouds and perhaps a brief rain or snow shower to the far
northern mountains.


Taking a look across the Northern Hemisphere we see a pool of
lurking cold Arctic air over central and northern Canada while warm
air continues to build and spread across most of the lower 48
states. Polar front separating the two air masses stays primarily to
our north, with most of the cold air surges heading more east than
south. The closest our area comes to seeing this cold air will be on
Monday when northern areas will be brushed by this cold as it heads
to the east.

On Monday the cold front which dropped south into the northern
half of the area during the overnight will lose its forward
momentum and get washed out during the heating of the day.
Should see temperatures warming from the bottom up over the
interior especially across central and western New England on
Monday, with temperatures peaking in the mid to upper 60s. 850
MB temperatures of around +4C in southern areas translates to
about 67-68F with good heating and mixing. But the light wind
flow will quickly develop an onshore component as the warming
land generates a sea breeze circulation and helps to reinforce
high pressure offshore. This should be a fairly early sea breeze
along coastal Maine and even into coastal New Hampshire, so
temperatures there will peak in the upper 50s to near 60 before
stalling or cooling in the afternoon. Farther to the north
temperatures peak out in the 40s to near 50 in the western Maine
mountains where colder air remains behind the dissolving front.

Onshore flow developing Monday afternoon will strengthen Monday
night into Tuesday as a cut off low over the Southeast US slowly
pulls northward up the East Coast. This will promote increasing
clouds and rain chances on Tuesday with a maritime air mass in
place keeping temperatures in the 40s, with some low 50s to the
west and north of the mountains. This onshore flow persists into
Wednesday as well, but with low level dewpoints on the increase.
Model forecast mid 50s dewpoints being advected in off the ocean
suggests widespread fog and drizzle are likely considering the
cold ocean surface temperatures. Weak surface low tracks near
Cape Cod and into the Gulf of Maine late Wednesday with the fog
and drizzle lasting through Wednesday night as there is not a
good clearing flow behind the low.

Should see a deeper south to southwesterly flow on Thursday as
the weakening cut off low moves east and we begin to be affected
by the next approaching wave moving through southern Canada.
Models diverge a bit on timing of this wave, with the ECMWF
surging this wave farther north while the GFS shoves it farther
east. Either way it should be a warm day Sunday with
temperatures warming into the 70s to possibly near 80 in the
southern New Hampshire warm spots while southerly winds keep
coastal Maine a little cooler due to the better onshore wind
component. Under the GFS scenario, a cold front will move into
western New England Thursday afternoon, sparking thunderstorms.
However, the ECMWF solution keeps the front much farther west
and ridging over our area would keep things dry for another
day. At this point the best that can be said is that a cold
front will move through Thursday or Friday with a chance of
showers as it does so. If it moves through during the daytime
there will be a better chance of thunderstorms, but if it goes
through at night it may not produce much in the way of
precipitation at all. The front lingers near the area into the
weekend which will keep a chance of showers in the forecast as
minor waves track along the stalled front.


Short Term...IFR or lower conditions are expected much of tonight on
the coastal plain. Farther west, improving conditions are expected
as the night wears on as high pressure builds in.
However, if skies clear out for a time, radiation fog and
stratus may form for a few hours before sunrise. VFR conditions
are expected area-wide Sunday and much of Sunday night.

Long Term...Should see VFR conditions on Monday, but an onshore
flow will bring increasing clouds Monday night into Tuesday,
with lowering ceilings to MVFR or IFR during the day Tuesday as
rain begins. Rain and drizzle will be widespread through
Wednesday night with IFR or worse conditions likely. Should see
improvement to VFR on Thursday as the onshore flow finally ends.


Short Term...A SCA for seas has been issued for the ocean waters
through 5 AM for 5-6 ft seas, which will decrease from east to
west. Otherwise, tranquil conditions are expected Sunday. Low-
end SCA conditions are possible Sunday night in advance of a
cold front.

Long Term...Flow becomes onshore on Monday as a sea breeze
circulation begins. The onshore flow gets reinforced Monday
night into Tuesday as low pressure slowly moves up the East Coast.
East to northeast winds increase to as high as 25 KT on Tuesday with
the onshore fetch promoting increasing wave heights with time.
Weakening low pressure moves through the Gulf of Maine Wednesday
night with winds becoming light as it does so. Waves will take a
while to subside and could stay above 5 FT through Friday.

Drying conditions are expected Sunday and Monday with min RH
values dropping back into the 30s and 40s under mainly light


We will be entering a period of high astronomical tides toward
the middle of the week. At Portland the astronomical tide is
forecast at 11 FT Tuesday night and 11.5 FT Wednesday night.
With a prolonged period of onshore flow expected, there will
likely be a minor storm surge of about 1 FT especially on
Tuesday evening when wind flow will be strongest. Minor coastal
flooding is possible during the Tuesday evening high tide. Winds
will be much lighter Wednesday night as low pressure moves
through the Gulf of Maine, but in the absence of a strong
clearing offshore flow there will likely be a lingering surge
which will maintain a threat for minor coastal flooding around
high tide.

The highest tides will be 11.7 FT early Friday morning and again
early Saturday morning with a light southerly flow unlikely to
cause a significant surge.


MARINE...Small Craft Advisory for hazardous seas until 5 AM EDT Sunday
     for ANZ150-152-154.



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