Portland, Maine 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

892
FXUS61 KGYX 040749
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
249 AM EST Wed Dec 4 2024

.SYNOPSIS...
A complex series of upper level troughs will cross the forecast
area tonight and Thursday with snowfall across the interior and
a mix of rain and snow closer to the coast. This system will be
a followed by a very cold airmass and gusty winds to finish up
the workweek and to start the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
Not a bad weather day today as the region will find itself in
short period of short wave ridging in a broad warm air advection
regime. Lots of clouds will be around but winds will be rather
light with high temperatures similar to yesterday`s readings.

Late in the day, a short wave trough will approach from the west
with attendant SFC low pressure. Forcing for ascent may be
strong enough by sunset to allow for some light snow to break
out in westernmost New Hampshire.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/...
The overall mass fields and thermal profiles for tonight in
association with redeveloping coastal low pressure have not
changed much in the various sources of guidance. The main fly in
the ointment is once pressure falls commence with the
developing low over Massachusetts, inland pointed warming winds
will also commence. This will aid in stronger forcing for ascent
to develop over the area, allowing for mainly snow to
overspread much of the region this evening.
On the other hand, there does not seem to be much of a
mechanism to keep the SFC cold air in place at the coast and
also portions of central ME as the southeasterlies strengthen.

While our snowfall forecast holds fairly high confidence in the
interior, there will be a stripe of much higher uncertainty
within 25-35 miles of the coast - perhaps even farther inland
from the Midcoast. Will the forcing for ascent be strong enough
on the nose of the low level jet to force 2" per hour snows for
a time just inland from the coast before it gets too warm? It`s
possible. But if the deeper omega fails to develop then it will
be much easier to change to rain earlier.

With that said, will keep all winter weather advisories in place
without any changes for the time being. It`s possible we`ll need
to add another row of zones closer to the coast (if anything for
the potential impact to the Thu morning commute) but will hold
off for the time being due to the uncertainty in thermal
profiles.

The main area of forcing leaves the area around 12z Thursday
allowing for much lighter precipitation during the day which
will allow for SFC warming and more iffy precip types,
especially on the coastal plain where  additional accums are
expected past mid to late morning.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Update...Overall trend in guidance is similar from Friday
through the weekend. Friday biggest hazard will be the strong
gusty winds and localized blowing snow concerns. This threat
will be limited due to the fact that water bodies aren`t frozen
over yet, which are one of the primary blowing snow source
regions. One trend that continues is for the warm front moving
further north the beginning of next week, will the potential for
more rain rather than mixed precipitation as most the area
should be in south of the frontal boundary. Will see if this
warming trend continues in the ensemble families.

Low pressure responsible for the snow Wednesday night and Thursday
is forecast to be centered over or just east of far northern Maine
Thursday evening. It will continue to lift northward into the
Canadian Maritimes through the course of Thursday night and Friday,
further tightening the pressure gradient across the region. Breezy
conditions will develop overnight Thursday and continue during the
day on Friday with forecast soundings supporting gusts of 30-35 mph
out of the W-WNW with a few possibly hitting the 40-45 mph range.
These gusty winds will make for a raw, blustery day with wind chills
in the teens, possibly even single digits in the morning hours south
of the mountains. In the mountains, wind chills will likely be in
the single digits either side of zero in the lower elevations and
well below zero in the higher terrain.

The mountains will also see upslope snow showers, and Froude numbers
from both the NAM/GFS suggest unblocked flow Thursday night and
Friday, so I do have some PoPs for snow showers south of the
mountains along with going above guidance on cloud cover. However,
by Friday afternoon, the low levels may dry out enough to where it`s
only flurries downwind of the mountains.

Even though winds will be diminishing Friday night, there may be a
period of subzero wind chills south of the mountains as temperatures
are forecast to become quite cold with single digits to teens for
lows. It will be partly sunny and not as breezy Saturday with
temperatures in the mid 20s to lower 30s for highs. A chance of snow
showers will continue in the mountains with a couple possibly
extending downwind into the foothills.

From Sunday into early next week...models are in pretty good
agreement showing low pressure moving across Quebec with some light
wintry precipitation possible along a warm front over portions of
the area on Sunday. For right now, the better chance will be across
northern areas. The 12Z operational GFS and ECWMF hint at a better
potential for precip early next week with low pressure across the
Great Lakes and potentially a stalled frontal boundary somewhere
across the area. There are mixed signals within the ensembles so I
have gone a touch lower than the NBM PoPs.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Short Term...VFR conditions expected thru today. Then as precip
overspreads the region conditions quickly drop to widespread IFR
or lower this evening. The exception may be north of the mtns...where
southerly winds keep places like HIE MVFR or VFR for much of the
event due to downsloping. IFR or lower conditions continue in
SN/RA thru Thu and begin to improve slowly by Thu afternoon.
Near the coast...especially PWM...AUG...and RKD...Wed night some
LLWS is possible as the LLJ swings thru the area.

Long Term...Mostly VFR Thursday night through Saturday except
for occasional MVFR ceilings and snow showers causing reduced
visibility at HIE. Thursday night and Friday will be breezy with
gusts out of the W-WNW 25 to 30 kt, possibly exceeding 35 kt
from time to time. There may also be a few snow showers develop
south of the mountains from late Friday morning into the
afternoon, but confidence on crossing any of the TAF sites is
low at the moment. A warm front looks to move through the region
around Sunday, potentially bringing a round of light wintry
precip and some degree of flight restrictions as well.

&&

.MARINE...
Short Term...Light winds continue for much of the day today. As
the clipper approaches a southerly LLJ will develop overnight. A
gale warning has been posted north of Cape Elizabeth for tonight.
There will likely be a pause in gale force wind gusts as LLJ
lifts northeast during the day on Thursday. However, westerly
gales are then expected to commence all waters by early Thu
evening.

Long Term...Westerly gales are likely Thursday night and Friday
as the deepening surface low lifts into the Canadian Maritimes,
further tightening the pressure gradient across the region.
Conditions improve Friday night but will probably remain above
SCA levels over the outer waters for most of the upcoming
weekend. Another low pressure may then cross the waters sometime
early next week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory from 7 PM this evening to noon EST
     Thursday for MEZ007>009-012>014-033.
NH...Winter Weather Advisory from 7 PM this evening to noon EST
     Thursday for NHZ001>009-011-015.
MARINE...Gale Warning from 7 PM this evening to 7 PM EST Friday for
     ANZ150>152.
     Small Craft Advisory from 4 PM this afternoon to 4 PM EST
     Thursday for ANZ153-154.
     Gale Watch from Thursday afternoon through Friday evening for
     ANZ153-154.

&&

$$


NEAR TERM...Ekster
SHORT TERM...Ekster
LONG TERM...Combs/DD