Area Forecast Discussion
Issued by NWS Portland, ME-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KGYX 280022
Area Forecast Discussion
National Weather Service Gray ME
822 PM EDT FRI MAY 27 2016
Warmer air will continue moving into the region through the first
part of the weekend...with the hottest temperatures expected for
Saturday. A few scattered showers or thunderstorms may pop up in
the afternoon. A cold front will push in from the northeast
Saturday night...and likely stall near the Connecticut valley and
southwest New Hampshire on Sunday...with onshore flow and cooler
temperatures across Maine and part of New Hampshire. Another front
approaches from the west Monday and makes for a mainly cloudy and
humid day with scattered showers and thunderstorms. High pressure
will move in for the remainder of the week yielding dry and
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
-- Changed Discussion --815 pm update: Increased pops across northern Somerset and
Franklin counties for the next few hours as thunderstorms
currently moving through that area. Fog continues to spread south
and west...considering high dewpoints over the cold atlantic
supersaturation occuring and some visibilities already down to a
1/4 mile in fog so am considering issuing a dense fog advisory
along the coast for the rest of the night. Will be monitoring the
fog situation along the coast and the adjacent inland areas
645 pm update: Visible satellite loops through the afternoon showed
widespread fog just offshore and along the immediate coastal areas
of the midcoast moving slowly west. With no mention of fog in
forecast...have made a significant update to forecast to include
this widespread fog over the waters and the coastal and inland
midcoast areas tonight as well as spreading the fog west into
southwest coastal Maine by late this evening. The question for
the remainder of the night will be how far inland the stratus and
fog move. Temperatures were adjusted based on latest obs.
Clouds have finally burned off over much of the coastal plain,
but visible satellite imagery shows clouds lingering just
offshore. The diurnal seabreeze circulation will push these
clouds onshore over the next few hours. Meanwhile a warm and
moist air mass to the west of the mountains continues to bubble
up with cumulus clouds and a few showers and thunderstorms over
New York, Vermont, and far western New Hampshire. This activity
may affect parts of southern and western New Hampshire at some
point this evening but it is not expected to be widespread.
Temperatures should drop into the 60s across most of New
Hampshire tonight, while 50s will be common across Maine where
the cooler maritime air will be felt.
-- End Changed Discussion --
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Weak low pressure moving toward the Gulf of Saint Lawrence will
send a frontal boundary through New Hampshire and Maine on
Saturday. Ahead of the front, winds will be out of the
west/northwest. This will allow the building heat and humidity to
our west to spill into the rest of New Hampshire and much of
western Maine. There is a fair amount of difference between the
NAM/GFS on low level temperatures tomorrow with the NAM about 3C
warmer than the GFS. As a result, the MOS numbers are pretty far
apart with the MET going for a high of 97 at Concord while the
MAV says only 88. Tend to favor the NAM in this case as it seems
to have a better handle on this air mass so far. Record high at
Concord is 94 and this appears to be in jeopardy. Dewpoints in the
low to mid 60s will allow heat index values to rise to 95 degrees
or higher in parts of southern/urban New Hampshire. Further to the
east along the coast a sea breeze will keep things a little
cooler. With the synoptic winds expected tomorrow, the sea breeze
will be most likely east of Portland.
With the heat and humidity building, there is some indication that
afternoon instability will be enough to generate showers and
thunderstorms. NAM is more aggressive with this, indicating CAPE
values above 1200 while the GFS is generally less than half that.
There is no obvious forcing mechanism for thunderstorms Saturday,
but the terrain and frontal boundary/sea breeze may be enough to
force some storms to fire during the afternoon. This activity
should diminish during the evening.
The cold front finishes its push southward and then westward
across the area Saturday night. A cool/moist onshore flow will be
in place across the area and cannot rule out some low clouds and
drizzle particularly over southeast New Hampshire and southwest
.LONG TERM /SUNDAY THROUGH FRIDAY/...
High impact weather: A few thunderstorms late Sunday night and
Monday could produce torrential downpours, and there is a low
risk for flash flooding.
The overall 500 mb pattern starts out summer-like, with strong
western Atlantic ridging in place. Although the ridge starts off
extending poleward to Newfoundland, several waves in the flow do
knock the ridge gradually back toward the equator. The temps will
moderate somewhat but will remain near to above normal thru next
week. A chance for showers come mid-late week as a cold front
moves thru, but there is no sign for any significant rainfall in
the extended forecast.
Sunday will start cool with onshore flow persisting behind the
back door front. Sunday looks to be mainly dry, but could be
fairly cloudy with the onshore flow, although some decent drying
above the marine layer could lead to some breaks of sunshine thru
the day. The best chance for showers or thunderstorms will be in
the north and western zones where the frontal boundary will be
sitting on sunday. In fact, CT valley region will likely be on the
warm and humid side, while elsewhere temps remain cooler, mainly
in the low-mid 60s coast to mid 70s in inland areas on the coastal
plain and the foothills.
Sunday night will see the marine layer start to erode a bit as
warmer pushes in aloft. Clouds will roll in and the threat of
showers will increase overnight...as will the humidity from SW to
NE. A cold front approaches from the west on Monday, and this will
set off showers and storms again in the warm moist air ahead of
the front. Even along the coast where marine layer will hold on,
should be enough elevated instability that we cannot rule out a
thunderstorm here on Monday. The big question is how much, if any,
moisture gets picked up from current fledgling tropical system in
the Atlantic. Models are in fair agreement that the system moves
west too the Carolina coast by Saturday night, but models vary
after that. Still could see some of that tropical air mass get
shunted northward ahead of the cold front and bring some heavy
rain in convective cells late Sunday into Monday, but confidence
remains low at this time.
Air mass behind the so-called cold front that passes Monday night
will remain warm and humid and will need to wait for second surge
of cooler air late Tue and Tue night. So Tue will be on the warm
and somewhat humid side, although with a fair amount of sun. This
secondary cold front moves thru with little fanfare...and may
produce a few scattered showers in the mountains on Tuesday. After
that temps drop back to near to a little above normal thru the
end of the week before another cold front approaches on Friday.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Short Term...Conditions start out VFR this afternoon for most
areas, though some low clouds are lurking just offshore. These
clouds will likely surge into coastal areas over the next few
hours, particularly from Portland eastward. This could bring
conditions to IFR or LIFR. Winds become southwesterly by morning
which should shift the focus for IFR clouds to eastern parts of
the area. This should burn off by mid morning with all areas
becoming VFR Saturday. Afternoon showers and storms are possible
especially over southern New Hampshire and southwest Maine though
the likelihood of affecting any particular TAF site is too low to
mention at this point.
Long Term...Sunday will start with some IFR, but will see some
improvement to MVFR or VFR during the day. A return to IFR
expected Sunday night lingering into Monday, with scattered
thunderstorms on Monday. VFR returns for Tue/Wed.
-- Changed Discussion --Short Term...Widespread dense fog over trhe waters tonight. Southwesterly
winds become northerly then northeasterly behind a cold front
Saturday evening. High pressure slides east into the Atlantic on
Sunday with winds becoming southeasterly. Winds through the period
should stay below 25 KT with wave heights fairly low as well.
Long Term...Winds seas will remain blow SCA conditions Sunday
-- End Changed Discussion --
Warm and humid conditions are expected Saturday. A cold front
brings cooler weather Sunday with a moist onshore flow over Maine
and eastern New Hampshire. Although showers and storms will be
possible Saturday and again early next week, no widespread
significant rainfall is forecast.