Area Forecast Discussion
Issued by NWS Portland, ME

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KGYX 110434
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1134 PM EST Sun Dec 10 2017

.SYNOPSIS...
Snow showers are expected to linger across the higher terrain
through Monday morning. An Arctic cold front will drop south
across the area early Monday. This boundary could trigger a few
snow squalls across the mountains and foothills with its
passage. The next low pressure system will affect Maine and New
Hampshire Tuesday and Wednesday with another round of wintry
precipitation. Colder weather follows this system for the end of
the work week.

&&

.NEAR TERM /TONIGHT/...
1130PM UPDATE...
Some clearer skies in the eastern part of the area have allowed
temperatures to drop there a bit more than forecast. Have
adjusted overnight temperatures to reflect this. Otherwise
forecast largely on track. Cold front dropping in from the north
will link up with some lake moisture and produce some light snow
in northern New Hampshire overnight.

8PM UPDATE...
Have made minor adjustments to hourly temperature and dewpoint
forecast based on latest observations. Dewpoints this evening
running a little higher than forecast so bumped these up a bit.
No other significant changes were made here.

4PM UPDATE...
Have updated the forecast to account for current snow shower
activity and structure precipitation chances such that they are
more graduated. Lake effect band is sending moisture into NH and
even western ME. Accumulation should be limited to
western/northern NH where an inch is possible overnight.

ORIGINAL DISCUSSION...
At 19z...a 984 millibar low was vicinity of Newfoundland. An
Arctic boundary extended from the Gaspe Peninsula through the
upper Great Lakes. As expected...the westerly trajectory to the
lee of Lake Ontario and upslope flow has produced a good deal of
cloudiness across the higher terrain...along with an area of
snow showers producing some light accumulations. Downwind of the
higher terrain we were seeing varying amounts of low clouds.
For tonight...a shortwave impulse will approach from the Great
Lakes late tonight. At the surface a weak wave will ripple
eastward along the Arctic boundary and help drive it southward
into the mountains after midnight. This should produce more
organized snow showers for a time...along with the possibility
of a brief snow squall with its passage. Elsewhere...skies will
average partly cloudy overnight with the chance of a brief snow
shower or flurry. Lows will range from the teens across the
mountains to the 20s elsewhere.

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
The shortwave and Arctic boundary exit the area by midday with
any lingering snow showers or flurries coming to an end. Highs
will be reached by midday with falling afternoon readings as the
Arctic air deepens across the area. We`ll see a brief break
late tomorrow into Monday night under weak ridging.
However...clouds will rapidly thicken and lower after midnight
in warm air advection ahead of the next disturbance. Expect
we`ll see precipitation breakout over much of New Hampshire and
southwest Maine during the predawn hours of Tuesday. The column
will be cold enough to support all snow at the onset.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Main Concerns for Tuesday through Sunday...

*Significant winter storm will bring additional snowfall to much
 of the area on Tuesday with possible mixing along the coast.
 This will impact rush hours on Tuesday.

*An Arctic air mass filters in for mid week creating very cold
 wind chills.

Blocking downstream over the Atlantic will keep deep troughing
over the northeastern CONUS with the northern jet stream/main
storm track overhead for the foreseeable future. It will become
colder locally with time with 700MB temperatures in the teens
by mid week. At its nadir (Thursday), the cold will translate
to tens and teens for the mountains and 20s and 30s south for
highs. Overnight lows will drop as the single digits north to
lower teens south.

A winter weather watch has been issued for Tuesday for all areas
except the coast and Waldo County. Many GEFS/NAEFS/ECMWF
ensemble members are in agreement that at least advisory level
snows will be seen all the way to the Canadian border, with
warning level criteria for much of southern and central NH and
southwest Maine. NAEFS percentiles, standardized anomalies, and
return intervals all indicate that this is an anomalously strong
system in relation to geopotential height falls and u and v
winds.

The latest deterministic model runs generally develop a secondary
low just along the NH/ME coast before curling it NNE into
northern Aroostook (aka "The County"). This path will draw in a
fair amount of warm air ahead of the cyclone and bring the
coastal front farther inland; thus the exclusion of the coast
in the watch. However, strong cold air damming will exist north
of the front especially in the foothills and we could see some
mixed precipitation along the interface. In general expect
p-type to be mainly snow once the system really wraps up with a
few hours of moderate to heavy snow. This system should move
out quickly very late Tuesday with some additional accumulating
snows in the slopes for Wednesday.

Gusty NW winds will arrive in its wake ushering in Arctic air.
Bitter windchill values are forecast north of the foothills
bottoming near -25 F Thursday morning, and a wind chill advisory
or warning may be needed.

Another system may affect the region Friday/Saturday but
currently it is dipping south of northern New England. In
general, with cyclonic flow in place clouds and showers will
remain in the extended forecast.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
Short Term...Areas of MVFR possible in snow showers north of the
mountains with local IFR conditions through Monday morning.
Elsewhere VFR is expected. MVFR will develop after 06z Tue and
lower to IFR by the end of the period in snow.

Long Term...A storm will impact the region on Tuesday. Expect
IFR in snow starting early Tuesday morning and continuing
through the day. Snow comes to an end late Tuesday night and
conditions will return to VFR by Wednesday expect in the upslope
mountain areas where MVFR SHSN will persist through Thursday.

&&

.MARINE...
Short Term...We`ll see one more surge of wind tonight into
Monday with SCA conditions likely. We should briefly drop below
SCA Monday night under weak ridging ahead of the next storm
system.

Long Term...A low will develop and cross the Gulf of Maine on
Tuesday bringing precipitation. In its wake northwesterly flow
will develop and strengthen to gale force by Wednesday night
under cold advection. Gales will subside by Thursday morning but
Small Craft advisories will persist through the end of the week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Watch from late Monday night through late Tuesday
     night for MEZ007>009-012>014-018>022.
NH...Winter Storm Watch from late Monday night through late Tuesday
     night for NHZ001>013-015.
MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ150>154.

&&

$$

NEAR TERM UPDATE...Kimble
SHORT TERM...Schwibs
LONG TERM...Hanes



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.