Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 050719
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
219 AM EST Thu Mar 5 2026

.WHAT HAS CHANGED...

No significant changes to the forecast...but appears the there will 
be more sleet than freezing rain tonight into Friday morning north 
of I-90. A small area across the southern Worcester Hills and 
southern Berks have the best chance of seeing freezing rain/ice 
accretion near or in excess of 0.25". Lastly...there is a low risk 
sleet changes to a burst of plowable snow across northern MA late 
tonight into Friday morning before the precipitation tapers off
by Friday afternoon. 

&&

.KEY MESSAGES...

- Rain develops today into early this evening & transitions to
  sleet & freezing rain across the high terrain as well as areas
  near and north of I-90 tonight into Fri am. Greatest risk for
  0.25"+ ice accretion high terrain of southern ORH
  Hills/southern Berks with an inch or two of sleet possible
  near and north of I-90. Lastly, low risk of a brief burst of
  plowable snow across northern MA before things tapers off by
  Fri afternoon to light rain/drizzle.

- Pattern change towards milder weather this weekend with a few
  rain showers followed by very warm temperatures next week. 

&&

.DISCUSSION...

Key Message 1...Rain develops today into early this evening & 
transitions to sleet & freezing rain across the high terrain as 
well as areas near and north of I-90 tonight into Fri am. 
Greatest risk for 0.25"+ ice accretion high terrain of southern 
ORH Hills/southern Berks with an inch or two of sleet possible 
near and north of I-90. Lastly, low risk of a brief burst of 
plowable snow across northern MA before things taper off by Fri 
afternoon.

A rather complex forecast today into Friday with a lot of moving 
parts...so we will break it down below. 

First off...any patchy dense ground fog that develops should scour 
out by mid morning or so. Otherwise...the focus will turn to a wave 
of low pressure that will be approaching from the west today. This 
will combined with a strong 1040+ mb high pressure system building 
into Quebec. The result will be a developing cool moist NE low level 
flow of air into southern New England. This will result in extensive 
low clouds today and high temps will be held in the upper 30s to 
near 40. As the low approaches from the west...mainly areas of light 
rain may overspread CT late in the morning and may reach RI/SE MA by 
early afternoon. However...dry low level air across northern and 
especially northeast MA will keep much of the region dry until 
perhaps until late afternoon or maybe early evening. 

The main concern though revolves around the weather tonight into Fri 
morning. Low pressure tracking towards the south coast will induce 
an area of modest speed convergence around 700 mb across southern New 
England. This will result in a period of good frontogenetic forcing 
resulting in the bulk of the precipitation tonight into Fri morning. 
Dynamic and adiabatic processes will result in precipitation 
changing to sleet and freezing rain near and north of I-90 as well 
as the higher elevations. In the lower elevations...Ptype will favor 
rain but there also might be some sleet involved. Some of the 
guidance and soundings indicate a fair amount of sleet across 
northern MA with 925T on the order of -3C to -5C. This would 
actually be a good thing as it would save much of the region from 
significant ice accretion. So hopefully this will keep ice accretion 
in the few hundredths to under 0.25 range for most locations. That 
being said...we will have to watch small area that perhaps may 
receive near or just over 0.25" of ice accretion. Greatest risk for that 
would be across the high terrain of the southern Berks/southern Worcester 
Hills where surface temps will be cold enough for an extended period 
of icing if the depth of the cold air remains shallow enough. While 
this risk looks to be over a small area...this will have to be 
watched for potential power outages if higher ice accretion is 
realized. Otherwise...near and north of I-90 appears the depth of 
the below freezing layer reaches 5000 feet. This should result in a 
lot of sleet and its possible areas near and especially north of I-90
receive an inch or two of mainly sleet. 

Lastly and perhaps the biggest wildcard in this event will be the 
potential for northern MA to flip to a burst of plowable snowfall 
late tonight into Fri morning before things taper off. Appears to be 
a low probability type of event...but soundings are very close to 
isothermal and if that happens a burst of accumulating 
snowfall may occur. Greatest risk for this appears to be in northern 
and especially northeast MA. Certainly something that forecasters 
will need to watch closely. A small difference in thermal profiles
will make the difference between mainly sleet or a burst of several
inches of snow. 

Regardless...the Fri am commute looks messy north of I-90 as well as 
for the higher terrain. Meanwhile...the lower elevations south of 
I-90 may see some sleet and perhaps isolated pockets of freezing 
rain with temps in the 32-34 degree range. However...probably most 
roadways end up wet especially with any bit of treatment. 

We should see precipitation taper off to mainly light rain/drizzle 
Fri afternoon as deeper forcing departs. However, areas of light 
rain/drizzle and fog look to continue especially across the eastern 
half of the region with moist shallow onshore flow.

Key Message 2...Pattern change towards milder weather this weekend 
with a few rain showers followed by very warm temperatures next 
week. 

A western Atlantic mid level ridge/surface high pressure then moves 
into place over the weekend and persists to some extent through at 
least the middle of next week with only one frontal system to speak 
of which suppresses it Saturday night into Sunday. Otherwise this 
spells a much different weather pattern than recently with dry and 
increasingly mild weather. For the weekend warm SW flow advects in a 
much warmer airmass overhead with 850 mb temps 12-13C. Boundary 
layer mixing, while poor on Saturday and unable to tap into the true 
warmth, improves going into next week. Regardless of shallow mixing 
and thick cloudcover Saturday, temps will be much warmer than Friday 
as surface flow finally backs to the SW with the exit of high 
pressure over QC; highs still make it into the low 50s in spots. 
After a weak frontal system brings scattered rain showers overnight, 
more sun arrives Sunday into next week accompanying the warmer 
airmass. Thus, high temperatures increase each day through at least 
Tuesday when mid to upper 60s are on the table! EPS ensemble 
guidance even wants to place a 40-50% chance of 70F in the 
Connecticut River valley on Tuesday...GEFS isn't as excited and 
we're a ways out but those hoping for an early taste of Spring can 
hold onto some hope. The next shortwave/cooldown arrives mid to late 
week. Aside from the rising temps, dewpoints will also be rising 
into the upper 40s will also contribute to quick melting of our 
snowpack, leading to potential for some rising rivers and streams 
late weekend into next week. Get ready to see some of those plants 
that have been buried since late January. 


&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

06z TAF Update...

Today...Moderate confidence.

Any patchy dense ground fog should burn off by mid-morning or 
so. Otherwise...widespread MVFR-IFR with localized LIFR 
conditions expected to overspread the region from southwest to 
northeast as the day wears along. Pockets of light rain will
mainly effect CT/RI/SE MA late this morning and especially this
afternoon. The rain will be slow to advance into northern and 
especially northeast MA...where it may not arrive until early 
evening. The rain may also begin to mix with sleet toward 
evening near and north of I-90. NE winds increasing to between 5
and 15 knots during the afternoon with the strongest of those 
winds near the coast.

Tonight and Friday...Moderate confidence.

IFR/LIFR conditions dominate in freezing rain and sleet in areas
north of I-90 as well as parts of the high terrain tonight. In
fact...sleet will probably be favored over freezing rain to the
north of I-90 by mid evening. South of I-90 in the lower 
elevation...Ptype mainly will be rain but some sleet may be 
mixed in at times. Ptype may mix with or change to snow late 
tonight into Fri morning for northern MA with the greatest risk 
north of route 2 into into northeast MA near the NH border. 
Precipitation tapers to mainly light rain/drizzle by Friday 
afternoon but IFR/LIFR conditions likely persist along with 
areas of fog. NE winds 5 to 15 knots with some 20-25 knot gusts 
possible near the coast.

KBOS Terminal...Moderate confidence in TAF. 

KBDL Terminal...Moderate confidence in TAF.

Outlook /Friday through Monday/...

Friday: Mainly IFR, with areas MVFR possible. Windy with local
gusts up to 30 kt. Chance RA, areas BR, FZRA likely, chance PL.

Friday Night: MVFR/IFR conditions possible. Slight chance FZRA.

Saturday: MVFR/IFR conditions possible. Breezy. Slight chance
RA, slight chance FZRA.

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

Sunday: VFR. Breezy. Slight chance RA.

Sunday Night through Monday: VFR. 

&&

.MARINE...
Forecaster Confidence Levels...

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

Today through Friday...High confidence.

Low pressure will approach from the west later today and pass to our 
south Friday morning. At the same time...a 1040+ mb high pressure system
will build across Quebec. This will generate increasing NE wind this afternoon 
into Friday. We expect NE wind gusts of 20 to 30 knots to develop later today 
and continue at times into Friday...so we have gone ahead and issued small craft
advisories for most of our waters. Seas will also become quite
choppy!

Outlook /Friday through Monday/...

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Areas of rough seas. Chance of rain, areas fog.
Areas of visibility 1 to 3 nm.

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

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

Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 8 ft. Chance of rain. 

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

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

Monday: Winds less than 25 kt. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 5 PM this afternoon to noon EST 
     Friday for CTZ002>004.
MA...Winter Weather Advisory from 5 PM this afternoon to noon EST 
     Friday for MAZ002>015-026.
RI...Winter Weather Advisory from 5 PM this afternoon to noon EST 
     Friday for RIZ001-003.
MARINE...Small Craft Advisory from 3 PM this afternoon to 7 PM EST 
     Friday for ANZ231>235-237-254>256.
     Small Craft Advisory from 11 AM this morning to 7 PM EST 
     Friday for ANZ250-251.

&&

$$

DISCUSSION...Frank/BW
AVIATION...Frank/BW
MARINE...Frank/BW