926
FXUS61 KBOX 010018
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
718 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

Thought the last few runs of the HRRR had a good handle on the
rainfall timing this evening. Used that as the basis for
tweaking the ending time overnight. rainfall had already ended
west of a line from Orange, MA to Hartford, CT. Expecting the
back edge of the rainfall to reach the I-95 corridor between
Boston and Providence about 10 PM, and finally move east of
Nantucket towards 2 AM.

Brought temperatures back in line with observed trends.

Previous Discussion...

Numerous showers across SNE will become focused across SE New
England 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 /00Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Tonight...High confidence in trends.

Rain exits 00-07z, followed by clearing and VFR. S gusts 20-25 kt
with areas of LLWS this evening over Cape/Islands associated
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, SN.

Tuesday Night: Mainly VFR, with areas IFR possible. Windy with
areas of gusts up to 30 kt. RA likely, chance SN.

Wednesday through Wednesday Night: VFR. Breezy.

Thursday: VFR. Windy with local gusts up to 30 kt.

Thursday Night: VFR. Windy with areas of gusts up to 30 kt.

Friday: VFR. Breezy.

&&

.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/...

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain.

Tuesday Night: Strong winds with gusts up to 40 kt. Areas of
rough seas. Rain. Local visibility 1 to 3 nm.

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Rough seas up to 10 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.

Thursday Night: Strong winds with gusts up to 45 kt. Rough seas
up to 15 ft.

Friday: Winds less than 25 kt. Local 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...Belk/KJC
SHORT TERM...KJC
LONG TERM...Dooley
AVIATION...Belk/KJC
MARINE...KJC/Dooley