Storm Watch 1, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
1249 PM EST Sat Feb 15 2025

.SYNOPSIS...
A storm system brings a round of wintry precipitation later
today into Sunday, starting as accumulating snow before
changing to rain near the coast and a wintry mix inland. Arctic
airmass in place for Monday and Tuesday along with strong
winds, especially Monday. Cold and dry for the middle of next
week, with another chance of snow later in the week with a
potential coastal system.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
10am Update...

12z Guidance is starting to roll in, and not seeing any major
deviations in the guidance since yesterday. Radar shows the
precipitation is still across western PA and NY, which will
take time to reach SNE. Still thinking snow will start late this
afternoon, around 4pm in the west, and 7pm in the east.

Key Messages...

* Dry in the morning and early afternoon for most.

* Snow arrives in from west to east 4-9 PM.

High pressure remains in control through the first half of the day
ahead of our next winter system. Some breaks of sun to be had across
southern New England in the morning but high clouds streaming
overhead on warm advection ahead of this evening's system will
thicken and lower through the day leading to mostly overcast skies.
At a synoptic scale we see the parent surface low over moving into
the midwest ahead of a digging shortwave trough which brings us
overspreading snow from west to east this evening. Model soundings
show the column saturating between 3 and 5 PM in western CT/MA which
is when we can expect the snow to begin. Moist advection continues
and this snow overspreads the rest of southern New England between 5
and 9 PM. More on this storm below.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Key Messages...

* 2 to 6 inches of snow followed by an icy mix and rain on Sunday.

Guidance didn't throw us any big curve balls with the 00Z suite as
we see broad WAA driven snowfall continuing over southern New
England in the evening and overnight hours. As has been advertised
the last several days, a developing mid level jet brings a warm nose
of air around 850 mb, moving in from SW to NE between midnight and 7
am. This will cause a changeover to sleet/freezing rain and
eventually all rain. One change from 24 hours ago is a delay in the
changeover, especially for areas further north as the warmer air
gets hung up a bit. This has allowed for slightly increased snow
totals over northern MA before the change; still thinking 4 to 6
inches is most likely with isolated amounts up to 7 inches. While
most locations will only be dealing with rain during the day on
Sunday, the exception will be the high terrain of the Worcester
Hills and Berkshires. Given a secondary low forming directly
overhead and directing colder NE flow into the region, there is some
question as to how quickly that subfreezing air gets scoured out for
northern MA in general, as models tend to be too fast. Regardless,
it will be a slushy, messy day for travel on Sunday. Given PWATs in
the 1.3" range and a 70-80 kt LLJ overhead, we will easily see 1-1.5
inches of rain on top of any snow that we get. This along with
melting snow as temps in southeast MA will reach up into the low to
mid 40s. Further north highs in the upper 30s are more likely,
outside of those higher elevations.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Messages:

* Increasing potential for at least advisory level winds for most
  parts of southern New England Monday with potential for periods
  near/at warning criteria for the higher elevations.

* Below normal temperatures, especially early next week. Windy
  conditions bring wind chills in as low as -10 Monday night.

* Monitoring potential for a coastal storm Weds-Thurs.

Details:

Sunday Night - Monday Night:

A strong cold front pushes through the region Sunday night. Strong
westerly subsident flow will kickstart the drying with any remaining
showers diminishing. Strong cold air advection will quickly drop
temperatures from mid 30s and mid 40s down to low-mid 20s.
Residual moisture/water on roads/paths will freeze which could
lead to slick spots if left untreated.

The ECMWF EFI shows a strong signal for anomalously high winds
Monday. With strong CAA advection and LLJ overhead, the potential
for strong gusts should be well supported. Model soundings indicate
a relatively deep, well-mixed boundary layer for points across
southern New England on Monday. This will allow transport of the
stronger winds aloft down to the surface. Soundings show around 50-
65 kts at the top of the mixed layer which in theory, would support
winds nearing high wind criteria in spots IF it fully mixed down.
The more likely scenario right now is widespread advisory level
winds. Ensemble guidance shows a high chance for gusts 45 mph (at
least) across southern New England. However, ensembles do indicate
probabilities of 60-90% confined to the higher terrain such as the
Worcester Hills and Berkshires for gusts nearing/or at warning
criteria (58 mph). With perpendicular flow to terrain of the
Berkshires, it is an ideal set-up for downslope enhancement, which
is why they (and the immediate east slope) display the highest
chances of reaching warning criteria. A High Wind Watch is looking
likely for this event. Will likely broad brush the whole region for
the Watch and upgrade to Warning/Advisories accordingly as we get
closer.

Temperatures Monday will be much cooler with highs in the mid 20s to
low 30s. However, gusty winds will make it feel much colder with
wind chills in the single digits to low teens. The higher gusts
gradually decrease Monday evening, but gusts will still play a
factor in how chilly it will feel overnight. Temperatures drop into
the single digits to teens with wind chills ranging from single
digits to as low as -5F.

Tuesday and Wednesday:

Windy conditions continue Tuesday; however, not as strong as Monday
as 850mb winds weaken. The well below normal airmass remains
positioned over the region resulting in chilly highs in the 20s.
Winds will bring wind chills into the single digits and teens again.
The pressure gradient continues to relax into Wednesday trending
winds downward. The airmass will begins to moderate as a weak ridge
builds in, "warming" highs back into the mid 20s to low 30s.

Thursday and Friday:

Confidence in the details of the pattern decrease late next week.
Overall, ensemble guidance continues to display a potential coastal
low forming in the mid-Atlantic then tracking northeastward toward
New England. Plenty of model spread among deterministic and ensemble
solutions and changes from run to run. As the track varies among
solutions/model runs, this will impact where the highest chances of
seeing precipitation will be and how much. With a cold pattern in
place, this would likely mean snow. Again, we are far out and there
is no consistency in the track so we will continue to monitor
this as more confidence trends become more evident.

&&

.AVIATION /18Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Rest of Today:

VFR the rest of Today with light winds. Light snow and MVFR CIGS
moves in from west to east this evening between 21z-00z.

Tonight:

Snow may become moderate to heavy overnight with 1/2in to 1.0 in
per hour snow rates. IFR/LIFR CIGS move in with heavier snow.
Snow transitions to light to moderate sleet from 06z-12z from
south to north. A bit of uncertainty on how long sleet lasts
before turning over to rain and freezing rain.

Sunday

For coastal areas, sleet should transition to rain with minimal
freezing rain. Rain will be heavy at times with rumbles of
thunder possible near the south coast. across the interior, but
outside the high terrain, freezing rain fallows the sleet, and
lasts until roughly 15z. In the high terrain. Freezing rain
could last for much of the afternoon. IFR/LIFR CIGS continue
through the afternoon.

Sunday Night.

Cold front sweeps through between 22z-02z, quickly ending any
remaining precip and raining CIGS back to VFR. Very windy behind
the cold front with gusts up to 50 knots.

KBOS TAF...High confidence through 18z Saturday. Moderate after.

KBDL TAF...High confidence through 18z Saturday. Moderate
after.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Mainly VFR, with local IFR possible. Strong winds
with gusts up to 45 kt. Chance RA, FZRA, chance SN.

Washingtons Birthday: Mainly VFR, with local MVFR possible.
Strong winds with gusts up to 45 kt.

Monday Night: VFR. Strong winds with local gusts up to 40 kt.

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

Tuesday Night through Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Moderate confidence.

Next storm approaches late today, so winds shift to the SE/S.
Could be small craft advisory conditions for southern waters by
late day. Better chance on Sunday as the low moves over the
region and winds start to increase. Initially they will be out
of the east, but as the low moves east, winds will switch to the
northwest and start to increase in strength. Gale Watches are in
effect for Sunday evening through Monday evening. Freezing
spray also becomes a problem late Monday into Tuesday.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Moderate risk for gale force winds with gusts up
to 45 kt. Rough seas up to 16 ft. Rain.

Washingtons Birthday: gale force winds with local gusts up to
45 kt. Rough seas up to 16 ft. Freezing spray likely.

Monday Night: gale force winds with gusts up to 40 kt. Rough
seas up to 15 ft. Freezing spray likely.

Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to
12 ft. Freezing spray likely.

Tuesday Night: Strong winds with gusts up to 30 kt. Rough seas
up to 10 ft.

Wednesday: Winds less than 25 kt. Local rough seas.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory until 7 PM EST Sunday for CTZ002>004.
     High Wind Watch from Sunday evening through Monday evening for
     CTZ002>004.
MA...Winter Weather Advisory until 7 PM EST Sunday for MAZ002>021-
     026.
     High Wind Watch from Sunday evening through Monday evening for
     MAZ002>024-026.
RI...Winter Weather Advisory until 7 PM EST Sunday for RIZ001>007.
     High Wind Watch from Sunday evening through Monday evening for
     RIZ001>008.
MARINE...Gale Watch from Sunday evening through Monday evening for
     ANZ230-236.
     Small Craft Advisory from 1 AM to 4 PM EST Sunday for
     ANZ231>235-237-250-251-254>256.
     Gale Watch from Sunday afternoon through Tuesday afternoon for
     ANZ231>235-237-250-251-254>256.

&&

SYNOPSIS...BW/Mensch
NEAR TERM...BW/KP
SHORT TERM...BW
LONG TERM...Mensch
AVIATION...KP
MARINE...BW/Mensch