Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 031939
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
239 PM EST Tue Mar 3 2026

.WHAT HAS CHANGED...
No significant changes regarding the wintry mix today into
tonight, but temperatures Wednesday lowered slightly to account
for lingering morning fog. Growing confidence on a rain- to- 
wintry mix transition Thursday night and Friday, possibly 
warranting winter weather headlines. Significant warmup this 
weekend into early next week, which could causes rises on 
smaller creeks and larger rivers as snow pack melts.

&&

.KEY MESSAGES...

- Mixed precipitation ongoing now through tonight. Snow 
  accumulations between a coating and 2" with ice accretion up to 
  0.10". Localized higher amounts to 0.25" possible in the higher 
  elevations.

- Areas of black ice possible early Wednesday morning, but
  otherwise drier and milder for the rest of the day.
  Temperatures may be slow to rise due to lingering fog.

- Wavy frontal boundary brings initial plain rain Thurs, but a 
  transition to a wintry mix of freezing rain/sleet for areas 
  north of the Mass Pike Thurs night into early Fri. Winter 
  Weather Advisories could be needed. Expect a chilly, raw 
  Friday after precip ends, with overcast and highs in the mid 
  30s.

- Pattern change toward milder temperatures remains in the 
  cards for the weekend. Snowmelt could cause within-bank rises 
  on streams, creeks and larger rivers.

&&

.DISCUSSION...

KEY MESSAGE 1...Mixed precipitation ongoing now through 
tonight. Snow accumulations between a coating and 2" with ice 
accretion up to 0.10". Localized higher amounts to 0.2" possible
in the higher elevations.

Mixed wintry precipitation (mostly snow at this time) is moving 
across southern New England from SW to NE as this is written, with 
predominantly rain being reported along the immediate south coast. 
Not much has changed with regards to expectations with this system; 
snow accumulations are still expected to be highest north of I-90, 
reaching up to 2". Most everywhere else can expect around a coating 
to an inch of snow before the switch over to sleet and freezing 
rain. Precipitation should switch over to mostly rain in the next 
few hours, between 5 pm and 8 pm, as midlevel warm air moves in. 
Surface temperatures northwest of I-95 will remain at or below 
freezing through tonight, which will increase the risk for freezing 
rain during the transition from snow. Ice accretion will likely be 
highest in the higher elevations of the Berkshires and Worcester 
Hills, ranging between 0.1" to even 0.2" in some spots. Untreated 
surfaces will likely turn icy tonight. Rain and drizzle will 
continue through tonight, ending around daybreak tomorrow as the 
shortwave continues eastward.

Lows tonight will mostly sit at or below freezing for most, with 
areas near the immediate coastlines more marginally above freezing.


KEY MESSAGE 2...Areas of black ice possible early Wednesday 
morning, but otherwise drier and milder for the rest of the day.
Temperatures may be slow to rise due to lingering fog.

Lingering low level moisture, light winds, and continued marginal 
temperatures will increase the risk for some areas of fog and black 
ice for early Wednesday morning. Lower temperatures in the interior 
could lend to some freezing fog in this environment, too. Depending 
on how long any fog sticks around, high temperatures tomorrow will 
also be a bit cooler than previously thought, especially in the CT 
Valley where fog has the highest chance of lingering until around 
noon given the weak winds. Local sea breezes along the immediate 
coasts would also keep temperatures lower there, aside from any 
lingering fog. Lowered daytime highs to account for this risk using 
CONSRaw and CONSShort guidance. Highs are still generally in the 
upper 40s and do reach 50F in some spots across the interior, with 
mid to low 40s along the immediate coasts.

Outside of any areas that see lingering fog, the subsidence 
following today's/tonight's shortwave will allow for significant 
sunshine and much drier, milder conditions. The midlevels dry out 
considerably, and weak high pressure builds in over the region for 
Wednesday. 850 mb temperatures increase to around 0C-4C and 925 mb 
temperatures increase to around 5C-7C Wednesday afternoon. This 
calmer period will not last long though, as the next chance for more 
unsettled weather will arrive Thursday with another passing 
shortwave disturbance.


KEY MESSAGE 3...Wavy frontal boundary brings initial plain rain
Thurs, but a transition to a wintry mix of freezing rain/sleet 
for areas north of the Mass Pike Thurs night into early Fri. 
Winter Weather Advisories could be needed. Expect a chilly, raw 
Friday after precip ends, with overcast and highs in the mid 
30s.

The next system in the parade of shortwave disturbances in WSWly 
flow aloft begins to affect Southern New England Thurs and lasts 
into the first part of Fri. This shortwave trough is now over the 
Colorado Rockies as of Tue late-morning, and is expected to drag an 
elongated, west-to-east frontal boundary northward to some extent in 
that Thurs to Fri timeframe. It now appears there are two main 
periods of precipitation. One comes in Thurs late-AM to early-PM 
with initial warm-advective burst, although will be falling as plain 
rain and QPF amts with this Thurs event look light. 

The somewhat bigger concern from a messaging standpoint however 
comes in during the Thurs early evening hours into early on Fri, as 
a more coherent wave of low pressure treks along the wavy frontal 
zone, while at the same time, shallow colder air entrenched over 
NH/ME surges southward in a cold-air-damming configuration. This 
allows for a transition from initial steady light rain Thurs evening 
to a wintry mix of sleet and freezing rain with the better potential 
for accreting icing around the higher terrain of the Berkshires, 
northern hills of Worcester County and in the Merrimack and MA 
portion of the CT Valleys. Although less impactful, it's notable 
that the surge of shallow cold air is robust enough such that even 
plain rain in locations south and east of the Mass Pike could be 
mixed with sleet during the overnight to early Fri AM hours, given 
950-925 mb temps drop to -2C as far south as southern CT. There are 
some forecast challenges and uncertainties which still need to be 
addressed, which include how far north will the warm front make it 
on Thurs/Thurs early evening (which affects how soon will any wintry 
precip begin to develop), and also the extent of QPF as model 
soundings start to dry out the layer above 850 mb. Current thinking 
is winter weather advisories could be needed for areas north of the 
Mass Pike; note that the anticipated precip-type-transition going 
from rain to wintry mix is an especially bad one from a road pre-
treatment standpoint, as those pre-treatments would be washed away 
by the initial period of plain rain. Given active weather/current 
winter weather headlines ongoing, will refrain from hoisting those 
with this shift but those could be forthcoming in the coming 
forecast updates insofar as model guidance continues to agree on 
that scenario. 

As precip ends Fri mid morning to noon from west to east, Fri 
overall looks to be a chilly and raw day; temperatures very likely 
going nowhere given both the stubborn overcast but also the shallow 
CAD/cold advection profile surges southward into the Lower Hudson 
Valley through the day on NE winds. Have made substantial edits to 
NBM temps as its usual diurnal curve is simply not appropriate for 
this non-diurnal temperature setup, and instead blended in a fair 
amount of NAM-based temps for Fri. This supports highs only in the 
mid 30s to maybe near 40 along the south coast of RI/MA. 


KEY MESSAGE 4...Pattern change toward milder temperatures 
remains in the cards for the weekend. Snowmelt could cause 
within-bank rises on streams, creeks and larger rivers.

Although Fri looks chilly and raw, a significant pattern change 
takes place for the weekend as anomalously strong SWly flow aloft 
advects in well above normal 850 mb temperatures Sat/Sun. These 
values could be as high as the mid-teens Celsius! These would be 
some 15 degrees Celsius warmer than climatological 850 mb temps for 
early March. While still warm, expectations should be tempered to an 
extent as both ECMWF/GFS show quite a bit of RH/cloud cover around 
and it's not likely we'll fully mix to that depth. Still, highs some 
10-15 degrees above normal should materialize for Sat/Sun with highs 
in the 50s to even some spot 60s. Rising dewpoints into the mid 
40s/around 50 will also eat away at the standing snow depth, too. 
There is a frontal system which looks to move in around Saturday 
night into Sunday, bringing light rains. Some rises on rivers could 
be anticipated during the weekend to early next week based on NAEFS 
MMEFS forecasts, mainly for the western watersheds.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

18z TAF Update...

Today...High confidence in trends with moderate confidence in 
timing/ptypes.

MVFR-IFR conditions. Ptype initially mainly snow to start this
afternoon for most. Change to rain from south to north occurs 
in the 20z to 01z timeframe along the coastal plain with a period
of sleet during the transition. Low chance for brief period of
freezing rain before a change over to rain. Snow/sleet 
transitioning to pockets of light freezing rain by early evening
for interior terminals. 

Tonight...High confidence in trends. Moderate for exact ptype. 

IFR to LIFR conditions expected tonight with periods of rain 
along the coastal plain and pockets of light freezing rain 
across parts of the interior. Winds generally less than 10 knots
today and tonight becoming WNW Wednesday morning. 

Wednesday...Moderate confidence (timing of improvement to VFR)

IFR improving to VFR early Wednesday morning. Lingering low
clouds/fog possible early AM. Lower confidence is exact timing 
of improvements to VFR. Ceilings should improve to VFR 11-16Z. 
NW winds 5-10 kts. 

KBOS Terminal...Moderate confidence (ptype today/tonight and 
VFR timing Wed).

Snow to start with a wintry mix/sleet possible after 22Z. 
Flipping to rain by 00z. Low risk for a brief period of freezing
rain before changing over to rain. Rain exits by 12Z. Slushy
coating of snow on runways. Visibilities bouncing between 2SM 
to as low as a 1/2SM worst case this evening/tonight. Moderate 
confidence in exact timing of improvements to VFR early 
Wednesday AM, but more likely between 10-13Z. 

KBDL Terminal...Moderate confidence in TAF. 

Snow flips to light rain/freezing rain 20-22z with perhaps a 
period of sleet during the transition. Temps this evening will 
be near freezing...so impacts may be somewhat limited on runways
but some icing can not be ruled out. Rain exits by 10Z
Wednesday. Lower confidence with timing of improvements to VFR,
but generally are expected to improve 13-16Z. Low stratus and 
BR/FG may linger early Wednesday morning with ceilings 
potentially not improving until late AM (worst case).

Outlook /Thursday through Sunday/...

Thursday: Mainly VFR, with local IFR possible. Chance RA,
slight chance FZRA.

Thursday Night: Mainly IFR, with areas MVFR possible. Breezy.
RA, PL, chance FZRA.

Friday: MVFR/IFR conditions possible. Breezy. RA likely, chance
FZRA.

Friday Night: Mainly VFR, with areas IFR possible. Slight
chance RA, slight chance FZRA.

Saturday: Mainly VFR, with local IFR possible. Breezy. Slight
chance RA.

Saturday Night: Mainly VFR, with local IFR possible. Breezy.
Chance RA.

Sunday: VFR. Slight chance RA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Wednesday Night...High confidence.

High pressure continues to move east of the waters today. This will 
result in long S-SW fetch and build seas into the 3 to 6 foot range 
late tonight into Wed across our southern waters. Small craft 
advisories remain in effect for our southern outer waters as a
result.

Seas start to diminish Wednesday night as Tuesday's disturbance
shifts further away from our waters and weak high pressure over
southern New England during the day Wednesday shifts over the
waters Wednesday night. S to SW winds become light to calm,
particularly over the southern waters.


Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain. Local visibility 1 nm or less.

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Rain likely. 

Friday: Winds less than 25 kt. Areas of rough seas. Rain
likely. 

Friday Night through Saturday: Winds less than 25 kt. Areas of
rough seas. Slight chance of rain. 

Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas. Chance of rain. 

Sunday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory until 7 AM EST Wednesday for 
     CTZ002>004.
MA...Winter Weather Advisory until 7 AM EST Wednesday for 
     MAZ002>012-014-026.
RI...Winter Weather Advisory until 7 AM EST Wednesday for RIZ001.
MARINE...Small Craft Advisory from 10 PM this evening to 7 PM EST 
     Wednesday for ANZ254>256.

&&

$$

DISCUSSION...Loconto/Hrencecin
AVIATION...Loconto/Hrencecin/Mensch
MARINE...Loconto/Hrencecin