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000
FXUS61 KGYX 280225
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1025 PM EDT Tue Oct 27 2020

.SYNOPSIS...
Cool high pressure builds into the area this evening before
moving offshore overnight. A weak disturbance may bring a few
showers to the area tomorrow. Towards the end of the work week,
low pressure tracks eastward to the south of New England just
as an Arctic cold front brings much colder air into the area
from the north. Rain is likely to begin in southern areas on
Thursday with rain changing to snow on Friday as the temperature
cools. This will be the first accumulating snow of the season
for many areas. Cold weather lasts through at least Saturday
before high pressure shifts east and allows temperatures to
slowly rebound.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Update...
Have issued an update as scattered rain and snow showers
continue to head southeast across southernmost portions of our
forecast area this evening. Latest mesoscale models show a
second batch of very light precipitation crossing southern
portions of the forecast area tonight into Wednesday morning.
Have modified pops across southern areas, however they still
remain relatively low, in the chance or slight chance category.
Some of the precipitation continues to fall into dry lower
levels and is evaporating before it reaches the ground. This dry
layer is depicted well by the 00Z GYX sounding which depicts an
unsaturated layer below 6500 feet.

Made minor adjustments to temperatures, dew points and winds in
the near and short term portion of the forecast. Otherwise,
this weak impulse will mostly bring clouds to the region, mainly
to southern areas.

Prev Disc...
Satellite imagery shows clearing across much of the
area associated with a cooler, drier air mass filtering in from
the north behind a departing boundary. Downsloping, gusty NW
winds have allowed stratus to clear out except for over the
mountains. Where we still have stratus there may be a few
flurries. Sunny skies over the coastal plain have helped
temperatures reach near of above 50 degrees. Across the higher
terrain we remain in the upper 30s to 40s.

Tonight skies become cloudy once again with a disturbance moving
towards southern New England. This may result in a few showers
across southern NH towards morning. Temperatures will be cold
with most areas seeing a hard freeze towards morning. We will
see chillier readings where skies are clear the longest, with
lower 20s across the north.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Low pressure deepens as it moves over Long Island and well south
of the Gulf of Maine during the afternoon hours Wednesday. This
may continue to brush southern sections with rain showers
through early afternoon before pushing east. Temperatures will
be just below normal with lower to mid 40s across much of the
area. Low to mid 50s will be possible along the coast and
southern NH.

WNW winds return Wednesday night and overnight lows will not be
quite as cool as tonight. We will see a familiar pattern with
skies clearing out later in the day before increasing after
dark ahead of the next surge of theta-e from the south.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Impacts: Low pressure passing south of the area will bring rain,
changing to snow across the region Thursday night into Friday.

Forecast Evolution: There are two features we are tracking for
Thursdays storm. First of all, Hurricane Zeta, which is
currently moving north through the Gulf of Mexico will move into
the Mississippi river delta region on Wednesday night and
undergo extra tropical transition as it moves inland. Aiding in
that transition will be an upper level low over the southwest
and surface cold front which has produced freezing rain over
Oklahoma. As both of these features move up the Ohio river
valley on Thursday they will interact. The result is a system
that upon exiting the east coast over NJ Thursday night will
contain tropical moisture, upper level support, and cold air.
These are all the ingredients necessary for a widespread early
season snowfall, how they combine still leaves plenty of
variability.

The operational deterministic models have been bouncing around
quite a bit, however the ensemble mean shows a more consistent
measured view. In this view the trend is for the low pressure to be
more elongated as the remains of Zeta outrun the upper level trough.
The result for New England is a decrease in both QPF and snowfall as
the best forcing for ascent passes to our south. Expect a sharp
gradient on the northern edge of the system, with this gradient
likely falling in the southern 1/2 of our CWA. With this in mind
have tried to tighten up the PoPs, keeping the far north dry,
while going to likely PoP on the Mass border. For temperatures,
it`s a complex system. With the NEly flow we typically see some
cold air damming and have kept the temps slightly lower through
the morning hours on Friday in deference to this however for
the cold air to dam it has to be there in the first place and
with the source of the cold to the NW behind the secondary
system, our NEly surface flow wont do as much to drop temps.
Further the ocean water remains relatively warm, thus expect
coastward of Rt 1 to remain in rain.

The overlap between the QPF and cold air is in the NW quadrant
of the storm, which falls in SW NH. This is where, especially at
the higher elevations of the monadnocks, we could see snowfall
amount over the current forecast as strong upward motion will be
present if the temperatures remain cold enough.

Snowfall amounts are still uncertain but what is becoming higher
confidence is for an accumulating snowfall event across southern NH.
With this being the first snow of the season for many expect impacts
to be higher than midwinter as trees with leaves, and a low level
jet allowing for winds of 20-30mph across the region overnight.

The storm will clear out Friday night, with cold high pressure
building in for the weekend. With all the focus on the snowfall,
have stuck with a consensus of the models for the weekend temps
as this was a higher confidence and lower impact time period.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Short Term...Mostly VFR through tonight, with some lingering
MVFR ceilings for KHIE. Lowering conditions to MVFR or perhaps
lower towards early morning for southern NH TAF sites,
spreading east towards coastal terminals by morning. We may see
-DZ, -RA, and fog at times before conditions improve after 18Z
 Wed, with occasional -SHSN possible at KHIE.

Long Term...Low pressure passing south of the region will push
rain into the region late Thursday resulting in IFR conditions
across the southern half of the CWA. Rain will change to snow
overnight as cold air moves into the region with IFR continuing
through Friday morning. Skies will clear Friday afternoon for
the coast with MVFR lingering the mountains overnight. VFR on
the weekend as high pressure builds into the region.

&&

.MARINE...
Short Term...Northwest winds will continue to gust to 20 knots
this afternoon over the outer waters in a relatively well mixed
environment before diminishing tonight. Winds and waves may
touch SCA conditions late tonight/early tomorrow morning with
low pressure in the area, mainly for the eastern outer waters.
However, this will be very limited so a SCA was not issued.

Long Term... NEly flow ahead of a system passing near the
benchmark Friday night will bring winds and seas to near SCA on
the outer waters. Behind the system on Friday night increasing
Cold air advection and NWly flow will result in SCA hold through
through the start of the weekend. High pressure will build in
for the weekend.

&&

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

&&

$$
JC/WW/MC