Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 110107

Area Forecast Discussion
National Weather Service Gray ME
807 PM EST Sun Dec 10 2023

A significant storm will overspread the area tonight through
tomorrow bringing flooding rainfall, damaging winds, and periods
of heavy snow across the north. Widespread 1-3 inches of rain is
expected with strong southerly winds along the coast and the I95
corridor. Upslope snow showers linger into midweek as a weak
cold front crosses the area before high pressure brings quieter
conditions for the end of the week.


805 PM Update...Made minimal changes to the forecast, and will
allow for the 00Z suite to start coming in before making any
more substantial changes. At this hour.... cool air is well
entrenched in all places except the Midcoast/Camden Hills area
and southern New Hampshire. This well-reflects the cooler trend
shown in hires guidance for the last several runs, owing to a
coastal front closer to the coast than prior model runs. This
would imply a lower overall wind threat through tonight and
Monday morning... with the exception of the Midcoast especially
closer toward Penobscot Bay, which still remains under the
proverbial gun of a quickly accelerating LLJ coming into New
England this evening. Will continue to monitor both upstream
observations for wind as well as local observations for
boundary layer conditions but overall no changes to hazards and
headlines necessary for now.

Previously...Rain has moved into the forecast area and will
continue thru most of the night. Rainfall at this time is the
hazard with the highest confidence. Hi-res guidance has
continued to trend up slightly with rainfall amounts today.
There is strong support now for pockets of rainfall in excess of
4 inches...with a widespread 2 to 3 inches elsewhere. With rain
focusing just west of the coastal front...that has increased
the flooding threat for many of the coastal river
valleys...including the Presumpscot...Kennebec...and well as Saco and Swift Valleys farther inland.
Flood watch remains in effect...and despite colder and and
snowier forecasts for the western ME mtns...the southern parts
of the zones could still see flooding. See the Hydrology section
below for more information.

Speaking of the snowfall forecast...the continued small ticks
east are allowing the CT River Valley and northern mtns to
remain colder and flash over to snow faster than previous
forecasts. Between midnight and sunrise rain will change to
snow...and very well may flash over to heavy snow as it does so.
Deep isothermal forecast soundings near freezing also support a
wet clingy type of snowfall...that will mean the power outage
threat is elevated from a typical snow. Downed limbs are
likely. With the snowier forecast...I have expanded the winter
weather advisory...but the zones have large ranges from a foot
near the Canadian little or no accumulation in the
southern portions.

Finally there is the damaging wind threat. Eastward ticks have
also kept the core of the LLJ out to sea...and really reduced
the coverage and duration of the highest gusts. Wind headlines
still look good north of Casco Bay...but from there southwest
confidence is very low. Winds may not be that gusty at
all...except for some initially gusty winds this evening before
the coastal front slips offshore. For now I will keep the
headlines as is...because it would not take much of a shift
west to bring the strong wind gust threat back to those areas.
Along the Midcoast...forecasts remain on track to push a portion
of the marine air mass inland around sunrise. Damaging winds
remain a threat.

There is a small chance of thunder if the low center can develop
far enough north...but with so many hazards out there I do not
feel the chances are high enough include in the forecast.
Similarly I did not get too cute about fog either. WAA and high
dewpoints over cold ground and snow will lead to patchy
fog...but I do not expect it to be as dense as last night.

Temps will be a non-diurnal trend...mostly steady overnight.


Cold front will quickly cross the area Mon morning...bringing
an end to the south wind threat. Just ahead of the cold
front...the coastal front will try and push deeper onshore. This
will be critical for determining how far inland damaging wind
gusts can make it before being pushed east. Models continue to
tick east...and keep that threat confined to near Penobscot headlines remain unchanged. Then CAA will begin and
increasing mixing depths with strong westerly winds on the
backside. There could be fairly widespread gusts of 40 mph with
this burst of CAA before settling back to 25 to 30 mph gusts
later in the afternoon.

Rain will also continue to changing to snow on the northwest
side of the low track. This will be the period when a quick
flash over to heavy snow is possible into the foothills. A quick
couple of inches in possible...and timed right around commute.
Will have to monitor timing for a potential expansion of winter
weather advisories to cover the travel hazard. Upslope snow
showers will continue into the overnight in the mtns.

Otherwise temps fall thru the day...dropping below freezing
overnight. While westerly winds usually do a fair job of drying
off pavement before this case several inches of
rain may be too much runoff and standing water to completely dry
before becoming slick. So refreezing on roads is a possibility
Mon night.


A narrow ridge will crest overhead Tuesday between two upper
level lows bringing clearing skies and seasonable temperatures
for the day. The next upper level low moves in Wednesday
bringing a cold front from the west with a return of upslope
snow showers. Temperatures will be similar to Tuesday through
the day before falling into the teens and 20s overnight. The
second half of the week will feature high pressure settling over
the Ohio River Valley before sliding to our south bringing
above normal temperatures for the end of the week. With New
England positioned on the outskirts of this high, some scattered
showers will be possible as low pressure remains to the north
with unsettled conditions dipping south into the area.
Precipitation amounts look to stay light throughout the extended


Short Term... The combination of low cigs and reduced vsby in
RA/FG/BR will bring IFR to LIFR conditions tonight across all
TAF sites. A low level jet will slide east across the area this
evening into tonight and will bring a period of LLWS from KMHT
to KCON and points east. Heavy rain will overspread the area
this evening and will persist into Monday morning while rain
changes to heavy wet snow at KHIE around 13Z and at KLEB around
15Z Monday. A front crosses the area during the day Monday
bringing wind shift out of the west with these winds gusting
around 25 kts Monday afternoon. Conditions improve south of the
mountains Monday afternoon with mainly VFR for Monday night
except at KHIE where upslope clouds and SHSN may linger through
Monday night.

Long Term... Mainly VFR conditions are expected Tuesday as low
pressure pulls away with westerly winds.  A cold front brings
scattered snow showers overnight into Wednesday with another round
of SHSN restrictions.  Conditions then return to VFR through the end
of the week as high pressure settles to our south.


Short Term...Southerly winds will gradually increase overnight.
Latest trends have been to push strongest winds farther out to
sea...but gusts approaching storm force are still possible by
midnight. The eastern most waters are the most likely to see
strong winds...and headlines should be good there. However I
cannot rule out the need for the waters north of Port Clyde to
Stonington needing a hurricane force wind warning. There is
more uncertainty for the western waters...but I have also held
headlines as is there because it would not take much of a tick
west to bring strong winds back. Winds shift to westerly midday
Mon and will remain gusty into the overnight. At least gale
conditions linger for all waters.

Long Term...Winds and seas will be gradually subsiding through
early next week, however conditions look to remain above SCA
thresholds through Wednesday as a cold front crosses the area.
High pressure then settles to the southwest for the end of the
week with seas remaining below SCA thresholds.


Rain will overspread the region tonight with increasing rates after
midnight. The initial rain and snowmelt will serve to prime the
system, then the additional rounds of heavy rainfall on Monday will
trigger flash flooding and widespread small stream and river
flooding. The cold and dry snowpack in the White Mountains and
Mountain Region of Maine will serve to limit any rainfall runoff,
however with the expectation of 1-3 inches, we can`t rule out small
stream responses in these areas. The snowpack from the foothills
southward will melt out with this event, contributing around a half
inch or more in runoff. The heaviest rainfall will occur in the
overrunning zone in the S facing slopes and extend down to the
coast. Latest storm track bring a swath of 3 to 5 inches from the
Presumpscot to the Penobscot River valleys. Particular concern for
flash flooding in these areas. The river response will be muted in
main stem rivers with only  minor flooding expected, with the
exception of the Kennebec where moderate flooding is expected.
Significant disruptions to travel is expected Monday from all the
road flooding likely to occur. One the rain transitions to snow the
runoff will slow down, with the focus on the main stem rivers by
Monday night. Flood warnings could continue Monday night into
Tuesday if flood waters are slow to recede.


ME...Flood Watch through Monday evening for MEZ007>009-012>014-
     Winter Weather Advisory from 1 AM to 7 PM EST Monday for
     Wind Advisory from 1 AM to 7 PM EST Monday for MEZ022>026.
     High Wind Warning from 1 AM to 7 PM EST Monday for MEZ027-028.
NH...Flood Watch through Monday evening for NHZ004>015.
     Winter Weather Advisory from 1 AM to 7 PM EST Monday for
     Wind Advisory from 1 AM to 7 PM EST Monday for NHZ014.
     Winter Storm Warning from 1 AM to 7 PM EST Monday for NHZ001.
MARINE...Storm Warning from 1 AM to 7 PM EST Monday for ANZ150>152-154.
     Gale Warning from 1 AM to 7 PM EST Monday for ANZ153.



LONG TERM...Thunberg
HYDROLOGY...Jamison is the U.S. government's official web portal to all federal, state and local government web resources and services.