Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 260405
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1205 AM EDT Tue Sep 26 2017

.SYNOPSIS...
High pressure will hold over the region tonight and will shift
east on Tuesday. A cold front will approach from the northwest
on Wednesday and will cross the region Wednesday night. Weak
high pressure will build over the region on Thursday. A
secondary cold front will drop south through the region on
Friday. High pressure will build in from the west over the
weekend.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1200 AM Update...
Have updated the forecast based on current conditions. Areas of
fog will be developing shortly, some of it will reduce the
visibility to near a quarter mile at times.

Have adjusted temperatures and dew point values with this latest
update. Lowered min temperatures most areas.

840 PM Update...
A dense fog advisory has been issued for the coastal plain as
well as southern NH. Other locations...including the mountains
and foothills...will see patchy dense fog...but it is not
expected to be as widespread as it will be to the south.


727 PM Update...
Minor changes this update for current temperature and dew point
readings.


505 PM Update...
Adjusted PoPs for this afternoon`s showers across the higher
terrain. Expect these to dissipate in the next couple of hours.
No lightning is noted with these showers. Adjusted fog for the
overnight and morning hours. A climate section was added below
with Manchester, Concord, and Augusta all breaking their high
temperature records today.


Previous discussion...
High pressure will hold over the region overnight. Expect
diurnal clouds and showers over the mountains to gradually clear
with the loss of heating this evening. High tds will result in
more dense valley fog overnight and may also affect coastal
areas. Lows overnight will will range from the mid 50s to mid
60s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
Unseasonably warm weather will continue on Tuesday as high
pressure slides east. Will likely see another round of showers
and possibly a few isolated thunderstorms....mainly over the
mountains and higher terrain. Highs will generally reach the mid
to upper 80s in inland locations. Once again a sea breeze will
cap temps in the mid 70s to near 80 along the coast.

Another warm and muggy night on tap for Tuesday night. Expect
any lingering evening showers to clear. More dense fog will be
likely in valley locations. Lows overnight will range from the
upper 50s to mid 60s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
The more active part of the extended is certainly the beginning.
We will see a continuation of the early fall heat Wed. Model
guidance continues to show H8 temps in excess of +17C. That is
supported by ensembles as well. I have increased temps from the
previous forecast...as this supports widespread temps in the mid
to upper 80s...if not lower 90s in the typical warm spots. This
would be enough to see a few more records fall as well. In
addition to the heat...we will have higher dew points too. And
this is likely to lead to afternoon MLCAPE in the 500-1000 J/kg
range...despite poor lapse rates aloft. With an approaching s/wv
trof and associated right entrance region of the H5 jet streak
we should see enough lift for at least scattered convection.
Forecast shear values on the order of 40 to 50 kts will be
favorable for storm organization...and SREF guidance is showing
an area of favorable conditions for strong to severe storms in
the region. The main question is timing at this point...and
whether or not storms can form and maintain before loss of
daytime heating. For now I have not added enhanced wording to
the grids...but that may be necessary with later shifts.

After the cold front pushes thru the forecast area Thu a
high pressure of continental origins settles in. This will bring
much cooler and drier wx than recent days. Given how warm it has
been though this is forecast to just bring temps back towards
normals. With the agreement in model guidance for the weekend
and beyond...I have gone with the multi-model consensus for days
4 thru 7.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
Short Term...VFR with areas of IFR/LIFR ceilings and vsby in
Morning fog.

Long Term...For the most part high pressure will be in control.
That means widespread VFR during the day...but valley fog and
LIFR conditions especially at LEB/HIE at night. We will have to
monitor marine fog/stratus Tue night...as a warm front tries to
lift N thru the region. That could bring an extended period of
IFR or lower conditions for coastal terminals as well.

&&

.MARINE...
Short Term...no flags.

Long Term...In general winds look to remain below SCA thresholds
thru the end of the week. Increased swell will still remain
thanks to Maria however...and a SCA for hazardous seas will
likely be necessary for late in the week.

&&

.TIDES/COASTAL FLOODING...
Southeast, long period swell will begin to increase from the mid
week period through the weekend. This will lead to an increased
risk of rip currents.

&&

.CLIMATE...
The following 3 sites broke their high temperature records
today:

Manchester reached 89 degrees at 3:20 PM, breaking the previous
record there of 87 in 1891.

Concord reached 90 degrees at 3:24 PM, breaking the previous
record there of 85 in 2007.

Augusta reached 88 degrees at 3:20 PM, breaking the previous
record there of 87 in 1891.

Portland reached 83 degrees and did NOT break their record of
88 set in 1970.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Dense Fog Advisory until 9 AM EDT this morning for MEZ018>028.
NH...Dense Fog Advisory until 9 AM EDT this morning for NHZ007-008-
     010>015.
MARINE...None.

&&

$$
JC


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