172
FXUS61 KBOX 302024
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
324 PM EST Sun Nov 30 2025

.SYNOPSIS...
Rain exits this evening as a cold front moves across the region. The
front will ushers in a return to drier, colder and blustery
conditions Monday. Low pressure tracking south of New England likely
brings accumulating snow to interior portions of CT and MA. However,
details regarding the rain/snow line and specific accumulations are
still quite uncertain.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Key Messages:

* Showers ending this evening, then clearing overnight

Numerous showers across SNE will become focused across SE New Eng
this evening within the axis of a modest low level jet and PWAT
plume. Meanwhile showers will be ending in the west by early evening
as a cold front moves into the region. The front will move across
rest of SNE by midnight with much drier air moving in behind it as
PWATs fall sharply. As a result rain will end from west to east 6 pm
to midnight, then clearing skies overnight. It will become somewhat
breezy in the post-frontal cold advection environment with west wind
gusts to 20 mph.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Key Messages:

* Blustery and cool Monday
* Light snow may develop before daybreak Tue across W MA/CT

Monday...

Mid level shortwave will be moving to the east early Monday with
subsidence and dry air leading to abundant sunshine. It will be
blustery as decent pressure gradient in place with well mixed
boundary layer supporting gusts up to 30 mph at times. Winds will
diminish late as high pres builds in from the west and gradient
relaxes. Chilly post frontal airmass with 925 mb temps -4 to -6C
supports highs in the mid 30s to lower 40s, with wind making it feel
several degrees colder.

Monday night...

High pres moves across New Eng Mon evening with decent radiational
cooling during the evening before clouds thicken as the high moves
offshore. Deep moisture remains to the west through 12z Tue and low
levels don`t moisten up until after 09z, so much of the region
should remain dry Mon night. But can`t rule out some light snow
breaking out across western MA/CT toward daybreak Tue. Lows will be
in the upper teens and 20s but rising overnight.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Key Messages:

* Coastal system Tuesday morning and night could bring plowable snow
  to some areas of southern New England. Although, there is a degree
  of uncertainty with the axis of greatest snowfall due to track
  variability. Winter Storm Watch issued for the central and western
  regions of Massachusetts.

* A few snow showers possible the second half of Thursday with the
  passage of an Arctic cold front, otherwise dry weather Wednesday
  through Friday. Turning unsettled by next weekend.

* Temperatures are trending well-below-average Wednesday through the
  upcoming weekend. An Arctic cold front Thursday night to bring the
  coldest air of the season, highs struggling to get above freezing
  by Friday afternoon.

Coastal low-pressure system ushers in unsettled winter conditions to
areas of southern New England, beginning Tuesday morning and ending
the predawn hours of Wednesday. Meaning there could be travel issues
for the morning and evening commute. Though, to be upfront, there is
a degree of uncertainty with the forecast due to variability within
the guidance of the low-pressure system. At this point, feel that
there are two possible outcomes, let`s can discuss those below as
scenario one and scenario two.

Scenario one, which will serve as the basis for the forecast would
keep the low-pressure system inside of 70N/40W, and is supported by
the GFS, NAM, and GEM. Onset of the precipitation Tuesday morning is
likely a singular PType, snow, due to the thermal profile from the
surface to 850mb remaining below freezing. This is short-lived as a
southerly LLJ leads to WAA, increasing temperatures above freezing
for areas outside of the higher terrain. There is plenty of moisture
to be had, origins are out of the Gulf. Probabilities of more than
0.5" of precipitation are 60-90 percent for the CWA. As for 1.0" or
greater, those are 20-40 percent, plenty to work with. Thinking this
event will be progressive as there is no blocking downstream over
the North Atlantic. As for the dynamic set up, the 750mb wave does
not close off until reaching eastern Gulf of Maine and the 850mb low
is nearly over southern New England, not a great set up for snowfall
in the lower elevations. While the coastal plain deals with a cold
rain, snowfall will be based in the higher elevations of central and
western Massachusetts. Given the uncertainties, there is a low to
moderate level of confidence the greatest snowfall, more than 6.0"
occurs in the northern hills of Worcester County and eastern slopes
of the Berkshires. Here GEFS have probabilities 40-60 percent, while
the CMC ENS are 80+ percent. Given the guidance mentioned above have
been in the same camp the past few days, opt`d to issue a Winter
Storm Watch in collaboration with neighboring WFOs and WPC for much
of Massachusetts west of I-95.

Scenario two is the outlier solution, though still worth paying
close attention, as the ECMWF and UKMET advertise the low-pressure
system passing further south. While the UKMET is joining this camp
the ECMWF has not deviated and what this solution does is shunts the
greatest axis of snow towards eastern Massachusetts and northern
areas of Rhode Island. The dynamic set up differs a bit from the
previous scenario with the 700mb wave closing off near Cape Cod and
the 850mb low just south of the islands. ECMWF ENS show probabilites
of 6.0" or more of snowfall between 50-70 percent across most of
eastern Massachusetts and northern Rhode Island. Lower probabilites
of 20-40 percent for western Massachusetts. Something to monitor,
especially as we enter the window for high-res guidance.

Wednesday through Sunday is quiet and cold. 500mb pattern becomes
somewhat zonal across much of the CONUS with surface high pressure
builds in behind the departing coastal low on Wednesday. Then an
Arctic cold frontal passage late in the day Thursday. Moisture is
limited, PWATS less than 0.6" should be enough for snow showers with
the frontal passage. With the Arctic cold front, 925mb temperatures
fall to -20C to -15C Thursday night, temperatures lower into the
single digits to low teens. But, a gusty northwest wind makes it
feel much colder, wind chills are below 0F across the higher terrain
and well into the single digits for the coastal plain. Towards the
end of the extended, guidance shows a more active pattern, leading
to unsettled conditions come next weekend.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

18Z update...

Through Tonight...High confidence in trends.

Lowering to MVFR with pockets of IFR as rain overspreads the
region. Rain exits 00-06z followed by clearing and VFR. S gusts
20-25 kt with areas of LLWS this evening over Cape/Islands
assocd with a low level jet. Winds shift to W by 06z with gusts
to 20-25 kt.

Monday...High Confidence.

VFR. NW gusts to 25 kt, diminishing late afternoon.

Monday night...High confidence.

VFR. Light snow with MVFR conditions may develop in western
MA/CT toward daybreak. Light to calm wind.

KBOS Terminal...High confidence in trends.

KBDL Terminal...High confidence in trends.

Outlook /Tuesday through Friday/...

Tuesday: Mainly IFR, with areas MVFR possible. Breezy. RA,
chance SN.

Tuesday Night: Mainly VFR, with local IFR possible. Breezy.
Chance SN, chance RA.

Wednesday through Wednesday Night: VFR. Breezy.

Thursday: Mainly VFR, with local MVFR possible. Windy with
local gusts up to 30 kt.

&&

.MARINE...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Through Monday night...High confidence.

Pre-frontal S-SW gusts to 25-30 kt will shift to W after midnight
then NW during Mon with gusts 25-30 kt continuing. SCA was issued
for all waters. Winds quickly diminish through Mon afternoon as high
pres builds in from the west. Light winds Mon evening becoming S-SE
toward daybreak. Rough seas over southern waters will begin to
subside during Mon and fall below 5 ft by Mon evening. Periods of
rain ending tonight from W to E. Dry with good vsbys Mon and
Mon night.

Outlook /Tuesday through Friday/...

Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Chance of rain. Areas of
visibility 1 to 3 nm.

Tuesday Night: Strong winds with gusts up to 35 kt. Areas of
rough seas. Chance of rain.

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Rough seas up to 11 ft.

Wednesday Night: Winds less than 25 kt. Seas up to 5 ft.

Thursday: Strong winds with gusts up to 40 kt. Areas of rough
seas.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Winter Storm Watch from Tuesday morning through late Tuesday
     night for MAZ002>006-008>012-026.
RI...None.
MARINE...Small Craft Advisory until 3 PM EST Monday for ANZ230-232>235-
     237.
     Small Craft Advisory until 5 PM EST Monday for ANZ231-250-251-
     254>256.
     Small Craft Advisory until 1 PM EST Monday for ANZ236.

&&

$$

SYNOPSIS...KJC/Dooley
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...Dooley
AVIATION...KJC
MARINE...KJC/Dooley