FXUS61 KGYX 081515

Area Forecast Discussion
National Weather Service Gray ME
1015 AM EST Fri Dec 8 2023

High pressure overhead today will bring slightly warmer temperatures
and mostly sunny skies. As this high pushes east for Saturday...
southerly winds will bring warmer temperatures...with 50s
likely south of the mountains by Sunday. A strong frontal system
arrives Sunday night and Monday with locally heavy rain...and
the potential for strong winds...especially along the coast.
Cooler and drier conditions arrive for the middle of next week.



10:15am Update... Knocked down highs by a degree or two for
today based on trends so far today and trends from the last
couple of days. Overall no notable changes with this update as
the forecast remains on track.

730 AM Update... Minor changes to reflect latest observational
trends. Stratus continues over western NH and therefore
increased cloud cover some across these areas to account for
this. Otherwise, mainly clear skies prevail elsewhere with
another cold morning underway.

Nighttime microphysics satellite imagery early this morning
shows a lingering stratus deck over much of western and northern
NH with some clearing now taking place over southern NH.
Elsewhere, skies are mostly clear, which has allowed
temperatures to fall into the single digits and teens. It will
continue to be a quiet but cold morning with temperatures
potentially falling a few additional degrees where skies remain

Surface high pressure will remain anchored over northern New England
today as mid-level shortwave ridging arrives from the west. This
will allow for mostly sunny skies and slightly warmer afternoon high
temperatures into the middle 30s to near 40 degrees south of the
foothills. Further to the north, highs will primarily be into the
20s to lower 30s.


Heights will continue to rise tonight as WAA aloft pushes h850
temperatures up to around +8C by dawn on Saturday. A weak sfc warm
front will approach from the southwest, which will result in
gradually increasing mid-level clouds overnight from southwest to
northeast. As a result, the coldest overnight lows will be found
across eastern areas with comparably warmer readings further to the
south and west. This places lows into the mid-20s across much of
south-central NH to the teens from roughly KIZG to KLEW and points
north and east.

Saturday will feature mostly cloudy skies and high temperatures once
again a few degrees warmer with readings into the upper 30s to mid-
40s from north to south. There is a low-end chance for some patchy
drizzle to develop late in the day across the foothills as seen on
the NAM as LL moisture increases but since the NAM often overdoes
the areal coverage of spotty precipitation and this is a period 3
forecast, will hold off on including this for now.


High Impact Weather Potential: Heavy rain and strong wind potential
Sunday night and Monday. Beyond this...little in the way of
significant weather impacts is expected.

--Pattern and Summary--

-NAO/-AO opens the period which has allowed for a chilly stretch
over the past few days...but pattern changes are in the works as the
downstream block near Greenland breaks down and allows Pacific
energy /+EPO/ to carve out a longwave trough across eastern North
America by the beginning of next week.  This will bring a surge of
warmer/moister air into the region before the trough swings in with
colder air for the middle of the week.  The longwave trough should
generally remain overhead through the end of the long term forecast
period with broad west northwest flow aloft and the potential for
some moisture-starved shortwaves to ripple through the region.
Thus...the primary forecast challenge will center on the frontal
system and associated low pressure that moves through the region
Sunday night and Monday.

--Daily Details--

Saturday Night - Sunday: The period opens with deep southwest flow
aloft as longwave trough deepens to our west.  PWATs surge above 1"
during the day Sunday with nearing frontal surface bringing
increasing chances for rain as the day progresses.  T8s push above
8C...but model sounding profiles suggest a pretty stout inversion
layer near the surface which will slow increasing temperatures and
keep winds light /esp away from the coast/ despite a
strengthening LLJ. Thus...expect increasing clouds through the
day with chances for rain increasing by late Sunday
afternoon/Sunday evening. Temperature forecast is challenging as
temps aloft will support lower/mid 50s but llevel inversion
will likely keep temperatures in the 30s north/40s south /see 2m
temps on the NAM/ until the rain arrives...with temperatures
continuing to rise into the Sunday night period.

Sunday Night - Monday: Upstream trough develops a negative tilt
as it drives into the northeast United States Sunday night and
Monday. This will cause cyclogenesis along the advancing cold
front with low pressure somewhere over southern ME/NH daybreak
Monday with this low strengthening as it pushes north and east
through the day. 00Z GFS shows pretty impressive deepening of
the low overhead on Monday /11mb in 6 hours/...which helps drive
warmer air and better mixing/stronger winds further into the
interior while the EC is weaker/later with low development and
actually closer to the GEFS mean. The GGEM is weaker
still...keeping the more fully mixed warm sector offshore. Have
followed pretty close to the EC/EC-EPS which confines the
strongest wind threat primary to the coast and into the Capitol
region of Maine. Wind advisories will likely be needed in these
areas...with some potential for warning level winds...esp for
the midcoast. There has been enough of a shift in the guidance
in the past 24-48 hours to warrant caution on any land-based
headlines with this package but will continue to mention the
wind /and rain/ potential in the morning Hazardous Weather

The warmest temperatures of the event come Sunday night as we
reach the low-mid 50s across southern NH and along the coastal
plain of Maine with temperatures beginning to fall by daybreak
Monday...with rain likely mixing with and changing to snow in
the mountains. Uncertainty remains with how quickly the cold air
arrives and therefore how much snow is realized. By Monday
evening...temperatures will be back in the 20s in the mountains
and 30s to the south and east.

As for rainfall...see Hydrology section below for more details..
but a significant amount of rain is looking likely...with
ensemble signals for 2" rather robust and in line with PWATs
pushing to around 1.4" as the frontal progression slows somewhat
as low pressure take shape along it with impressive +DPVA and
right entrance region jet forcing.

Finally...with warming dewpoints late Sunday and through Sunday
night...expect that we/ll see some fog development as the cool
ground surface maintains near surface saturation of the moist

Tuesday - Thursday:  A more seasonable end to the forecast period is
in store as a high pressure ridge axis builds in Monday night and
Tuesday.  High pressure remains anchored over the southeastern
United States through Thursday with westerly flow aloft generally
dominating across our region.  For Tuesday and Wednesday...highs
looks to still reach a bit above normal with highs around 30 in the
mountains...and in the upper 30s to around 40 south.  A weak and
moisture-starved northern stream wave and associated cold front
pushes through Tuesday night into Wednesday with perhaps some
mountain snow showers.  This will usher in somewhat cooler
temperatures on Thursday with highs in the 20s north and 30s


Short Term...VFR conditions to dominate through at least early
Sunday morning along with light and variable winds. The
exception will be at KHIE and KLEB where MVFR CIGs will persist
through around 12-14Z today. Ceilings will gradually begin
lowering late Sunday ahead of our next storm system. No LLWS is
expected at this time.

Long Term...Some stratus and fog is possible Saturday
night...but the much greater potential for restrictions will
come late Sunday through early Monday with IFR CIGS/VSBYS likely
in fog and rain. There may also be a period of LLWS during the
day Sunday before stronger winds reach down to the surface.
Sunday night into early Monday...strong south/southwest wind
gusts 35-45kt are possible along the coast... with gusts
20-30kts inland. Improving conditions are expected late Monday
through the remainder of the period though westerly winds will
remain gusty.


Short Term...Winds and seas to remain below thresholds hazardous
to small crafts through Saturday night as high pressure settles
over the waters. Southerly winds will begin increasing on Sunday
ahead of our next storm system with conditions becoming
hazardous to small crafts. Light freezing spray will remain
possible across western Penobscot Bay through early this

Long Term...Have hoisted gale watches for the period late
Sunday through Monday night. Ensemble probabilities of 34kt are
over 50% and while there remain some significant differences in
the details...gales look likely. Storm force gusts are possible
as well in the stronger end of the guidance envelope...but
confidence not high enough at this range to go with storm
watches. Thanks CAR/BOX for the collab.


There is strong deterministic/ensemble agreement for a
significant rainfall event for the Sunday afternoon-Monday
morning timeframe. 2" rainfall probabilities have increased over
the past 24 hours and are focused in the upslope region of the
mountains. The bigger question mark...as noted yesterday...is
the amount of SWE we can melt out of the mountains. Guidance has
been lowering the max dewpoint temperatures in the terrain...
such that it is possible dewpoints never reach much above 40.
Also...temperatures begin fall on Monday...switching rain back
to snow in the mountains. So...expect we/ll melt out the snow
over the coastal plain and possibly into the foothills...with
added snowmelt uncertain to the north of this. This will bring
the potential for river flooding...particularly on the
smaller/headwaters streams.

Rainfall rates Monday morning may allow for some poor drainage
flooding as well...though a widespread flash flood threat is not


MARINE...Gale Watch from Sunday afternoon through Monday evening for


LONG TERM...Arnott