Brockton, Massachusetts 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

515
FXUS61 KBOX 201924
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
224 PM EST Sat Dec 20 2025

.WHAT HAS CHANGED...

Small Craft Advisories and Gale Watches upgraded to Gale
Warnings. Small Craft Advisories hoisted for Narraganset Bay and
Boston Harbor. Confidence in minor snow accumulations has
increased on Tuesday...particularly across interior southern New
England. High uncertainty on temperatures Friday into next
weekend.

&&

.KEY MESSAGES...

- Gusty southwest winds overnight especially at higher elevations
  and near the coast.

- Turning much colder Sunday night into Monday with gusty
  northwest winds.

- Minor accumulating snow expected Tue especially across the
  interior where 1-3" seems reasonable with localized 4" amounts
  possible in the higher terrain.

- Dry with highs in the 30s to lower 40s follow Wed & Thu /Christmas Day/
  but will be quite blustery Wed with less wind Thu /Christmas/.

- Low confidence forecast Fri into next weekend with unseasonably
  mild temps to our southwest and very cold air just to our north.
  Shallow cold air and wintry mix possible at times in our region.

&&

.DISCUSSION...

KEY MESSAGE 1...Period of gusty southwest winds overnight tonight.

High pressure will be slow to move offshore overnight. At the same
time an area of low pressure over southern Canada moves towards
northern New England. The resulting pressure gradient will bring a
period of gusty SW winds tonight especially over higher terrain and
along immediate coast where SW gusts to 25-35 mph expected. 15-25
mph gusts elsewhere. Clouds increase tonight but dry weather will
prevail with steady or slowly rising temps overnight as winds
increase.

KEY MESSAGE 2...Turning colder and blustery late Sun into Sun night

Strong cold front swings through from west to east between 15-18z.
Dry FROPA expected with a bone dry column and PWATS around 0.10
inches. Thus, went with the NBM with near-zero POPs for the region
tomorrow. Expecting a gusty SW wind ahead of the front, namely for
coastal locations where better mixing is present. Will likely see
gusts around 25-35 mph. Increasing PBL heights and a 45kt LLJ behind
the front will bring similar winds later Sunday into Monday morning.
Winds gradually diminish through Monday as the pressure gradient
weakens. Seasonable temps Sun ahead of the front then falling temps
behind the front Sun afternoon, especially interior and turning much
colder Sun night as 850 mb temps bottom out at -12 to -15C. Wind
chills by Mon morning will drop to 5-10F and near zero in the
Berkshires. Temps will be several degrees below normal Mon with
highs upper 20s and lower 30s and plentiful sunshine in very dry
airmass.

KEY MESSAGE 3...Minor accumulating snow expected Tue especially
across the interior where 1-3" seems reasonable with
perhaps localized 4" amounts possible across the higher terrain.

A ridge of high pressure moves off the coast as a fast moving low
pressure system approaches from the west on Tue. This combination
will result in WAA developing across southern New England. An
initially cold boundary layer should allow for snow to develop in
most locations near daybreak Tue. Given that there is not a surface
high pressure system in eastern Canada and assuming that the surface
low tracks to our north...would expect Ptype issues to develop near
and especially southeast of I-95 Tue afternoon. Regardless...this
looks to be a minor snow event with the greatest risk across the
interior where boundary layer issues are less of a concern.
Currently...thinking 1-3" of snow seems reasonable especially across
interior southern New England with perhaps some localized 4" amounts
in the higher terrain.

That being said...there is still uncertainty given this is a Day 3
forecast. The 12z GFS operational run is a big outlier that is
further south with the low pressure system than the rest of the
guidance...this results in colder thermal profiles. It also
indicates additional QPF Tue night with an inverted trough setup. We
think this is a very low probability because it does not even have
support from most of its individual ensembles...but would bring the
potential of several inches of snow right to the I-95 corridor.

KEY MESSAGE 4...Dry with highs in the 30s to lower 40s follow Wed &
Thu /Christmas Day/ but will be quite blustery Wed with less wind
Thu /Christmas/.

Low pressure will intensify significantly as it moves east and away
from the region. This combined with high pressure over the Great
Lakes will result in dry/blustery conditions with chilly temps Wed.
A ridge of high pressure builds to our south Thu resulting in
dry/seasonable chilly temperatures but with less wind. High temps
Wed and Thu /Christmas/ will be in the 30s to the lower 40s with
Christmas being the milder day.

KEY MESSAGE 5...Low confidence forecast Fri into next weekend with
unseasonably mild temps to our southwest and very cold air just to
our north. Shallow cold air and wintry mix possible at times.

A very difficult forecast Friday into next weekend given our region
may end up in the battle zone. Unseasonably mild weather just to our
southwest with very cold/below normal winter-like temperatures just
to our north and northeast. We may be dealing with shallow cold air
at times and perhaps a bit of rain/ice and/or snow at times. Not
much more we can say at this point...but appears we may not share in
the unseasonably mild temps much of the time impacting most of the
lower 48.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...

Forecaster Confidence Levels...

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

18z TAF Update...no significant changes.

Tonight through Saturday...High Confidence in trends

VFR conditions expected. SW winds through this afternoon and
tonight. SW gusts 25-30 kts resume late tonight into Sunday
morning, mainly along the immediate coast and Islands and higher
terrain.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: VFR. Breezy.

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

Tuesday Night: Mainly VFR, with local IFR possible. Windy with
gusts up to 35 kt. Chance SHRA, slight chance SHSN.

Wednesday: VFR. Windy with gusts up to 35 kt.

Wednesday Night: VFR. Breezy.

Christmas Day: VFR. Breezy. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Monday...High Confidence.

Southwesterly gales develop tonight ahead of a cold front. Winds of
25-35 kts expected with gusts as high as 40 kts. Gale warnings for
the inner and outer coastal waters go into effect at 06z tonight and
go through 12z Monday morning. Elsewhere, Small Craft Advisories for
Narragansett Bay and Boston Harbor. Gradual improvements on Monday.

Outlook /Monday Night through Thursday/...

Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft.

Tuesday: Moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Local rough seas. Rain likely, snow
likely. Local visibility 1 to 3 nm.

Tuesday Night: Low risk for gale force winds with local gusts
up to 45 kt. Areas of rough seas. Chance of rain showers.

Wednesday: Moderate risk for gale force winds with local gusts
up to 45 kt. Areas of rough seas. Slight chance of rain
showers.

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.

Christmas Day: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 1 AM Sunday to 7 AM EST Monday for
     ANZ230-236.
     Gale Warning from 1 AM Sunday to 7 AM EST Monday for
     ANZ231>235-237-250-251-254>256.

&&

$$

DISCUSSION...FT/Frank
AVIATION...FT/Frank
MARINE...FT/Frank