Heavy Snow in Massachusetts, February 9, 2025

Area Forecast Discussion
National Weather Service Boston/Norton MA
856 PM EST Sat Feb 8 2025

.SYNOPSIS...
Snow overspreads Southern New England this evening, becoming heavy
at times overnight into early Sunday morning, with perhaps some mix
of sleet and freezing rain before ending. A widespread 5 to 9 inches
is expected regionwide, with a low probability (10-20% chance) of 10-
12 inches possible across northern MA, including the city of Boston.
Drying out Sunday afternoon through Tuesday, with a period of below
normal temperatures and limited if any snowmelt from tonight's
storm. Our weather pattern then becomes more active again with a
coastal low pressure passing to our south Tuesday night into
Wednesday, that may bring light snow, then monitoring a stronger
storm around late next week.

&&

.NEAR TERM /THROUGH SUNDAY/...

Update: 845PM - Light snow has arrived across western parts of
southern New England and the snow will continue to push east the
next two hours. Conditions will only continue to deteriorate at
this point. This evening, SPC highlighted southern New England
in their mesoscale discussion for heavy snowfall rates of 1-2"
per hour with the leading edge of the moisture. In general,
have not made any significant adjustments to the forecast, but
will reevaluate the high-res 00z as it comes in and make any
course adjustments if necessary.

Please see the full details for the upcoming storm below.

Previous forecast discussion,

Key Messages:

* Widespread snowfall of 5-9" tonight into Sunday morning, with
  highest amounts across northern MA, and a low prob (10-20% chance)
  of 10-12" in spots over northern MA to the VT/MA border.

* Heaviest snow 11 PM to 5 AM from west to east, with snowfall rates
  of 1-2" hr possible, highest probability across northern MA. Snow
  may end Sunday morning as a period of sleet and/or freezing rain,
  except rain along the south coast.

* Snow covered roads and poor visibility yield difficult travel
  overnight.

Synoptics...

Northern stream short wave moves across the Great Lakes this evening
with parent low pressure over the OH Valley. As both of these
features traverse eastward tonight, secondary low develops along
baroclinic zone near 40N, with coastal low becoming the dominant low
level circulation, tracking from the DE coast to over the 40N/70W
benchmark 12z Sunday. This will lock in low level cold air across
SNE, which is abundant this evening, with dew pts currently in the
teens all the way southward to the islands.

Impacts...

Snowfall and ptype: two bands of snow are expected, first from
approximately 03z-09z from west to east, with initial burst of mid
level WAA. Per Fgen fields, this snow band should be robust with
hourly rates of 1-2 inches given magnitude of Fgen, some weak
elevated instability and high SLR with forcing in the -10C to -12C
layer. The strongest part of this band traverses northern MA, with
weaker values across CT/RI/SE MA. This will be fast moving
band/short duration given the mid/upper level wave remains open.
However, at 850 mb, it's a closed circulation with strong Fgen as
CCB develops across CT/RI/SE MA from about 09z-15z. This band will
not be a robust with forcing for ascent beneath the DBZ, thus lower
SLR, but still modest snowfall rates of up to 1 inch per hour at
times. Warm nose around 800 mb per model soundings may yield some
sleet/ice pellets across CT/RI/SE MA. Also, dry slot races across
CT/RI and SE MA 09-12z, this may result in snow ending as freezing
drizzle and just rain for the immediate south coast, especially the
the islands. This region remains in an advisory for 4-6 inches.
Elsewhere, a widespread 5-9 inches is expected, with the lower
totals over CT/RI/SE MA given mixed ptype possible towards the end
of the event. The higher totals expected across northern MA, where
dry slot traverses south of this region. Given dry slot may remain
south of northern MA, longer duration of snow combined with
proximity to more intense WAA snow band, there is a low prob (10-
20%) of 10-12" across northern MA to the VT/NH border,possibly as
far south as Boston.

Timing: snow overspreads the region this evening roughly from 8 pm
to 11 pm and quickly becomes moderate to heavy at times. The
heaviest snow will then fall from 11 AM to 5 AM from west to east.
Snow intensity slackens after 5 MA but likely still accumulates
through 7 AM across RI and eastern-central MA, possibly lingering
until midday over coastal eastern MA. Dry weather prevails all areas
Sunday afternoon.

Travel: given the recent cold weather, snow will quickly stick and
accumulate with roads becoming snow covered by midnight all areas.
Moderate to heavy snow at times overnight will result in poor
visibility, exacerbate the difficult travel conditions, along with
the potential sleet and freezing rain mixing in at times Sunday
morning.

Headlines: no changes with Winter Storm warnings remaining posted
for much of the area for widespread 5-9 inches, except winter
weather advisories for the Cape and Islands, given less snowfall, 4-
6 inches.

Winds: given this is a weak, low amplitude wave, fairly light winds
are expected.

Snow character: snow will be mainly dry/fluffy for this event, but
as the dry slot approaches late tonight/early Sunday morning,
freezing drizzle and possibly sleet across CT/RI/SE MA (snow to
rain south coast and islands) snow will have an icy finish to it.

Forecast confidence/uncertainty: how quick dry slot overspreads the
area will impact final snow totals, along with how far south initial
intense snow band traverses (into northern MA or farther north
straddling VT/NH/MA border?). High confidence for a widespread 5-9"
snowfall, with a south to north gradient, highest amounts northern
MA. Lower confidence in double digit snow amounts, but if it were to
happen would be across northern MA to VT/NH border where deeper
moisture persist longer.

Sunday afternoon...

Dry weather with subsidence behind departing wave. Some breaks of
sunshine possible before sunset. Chilly with highs only 30-35 and a
modest N-NW wind.

&&

.SHORT TERM /SUNDAY NIGHT/...
Sunday night...

Weak short wave riding supports dry weather and mostly clear
conditions, along with a light NNW wind. This combined with a
refresh snowcover, followed the coldest guidance, yielding lows in
the single digits and teens.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
340 PM update...

Key Messages:

* Weak system tracks to the south Tuesday early Wednesday with
  potential for light snow mainly for the south coast and Cape and
  Islands.

* Storm system moves across region Thursday bringing another
  potential round of wintry precipitation

The extended period will feature a more zonal pattern aloft to start
with the passage of a system to the south of southern New England.
By the end of the week, there is a general consensus among guidance
for a transition to less zonal flow with potential for another
larger scale system bringing widespread precipitation.

High pressure will owe to dry conditions Monday with a cooler
airmass in place. Highs range in the low to mid 30s across the
region.

A weak mid-level shortwave moves across in the Tuesday to Wednesday
timeframe. Deterministic and ensemble guidance show general
agreement with the surface low tracking south of the region with
potential for a shield of light precipitation north of the low brush
southern New England. With cold air in place, this will make it
simple with any precipitation falling as snow. There is still spread
among ensemble guidance in how far north this light precipitation
extends resulting in a range among members from light QPF amounts to
no precipitation at all for locations. The highest probabilities for
seeing a light accumulation of snow will be confined to the south
shore and Cape/Islands with lower probabilities (< 40%) for more
northward areas such as Boston. Either way, accumulations will be
light.

Not long after this quick weaker wave, a stronger wave originating
from southern Rockies approaches the northeast. There appears to be
good agreement with synoptic support for ascent with southern New
England in the right entrance region of the upper level jet.
Ensemble means shows ample moisture transport with this system with
precipitable water values 250-300% of normal as it quickly tracks
northeastward across the region. Antecedent cold air should
support snowfall on the front end of the system with model
guidance showing the presence of a warm front moving across
owing to precipitation type changes/complexities on the back end
of the system. This system is pretty far out and track
differences will impact snow amounts and precipitation type.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

00z update...

Overnight...High Confidence on trends, but some uncertainty on
exact timing of details.

Snow quickly overspreads the region between 02z western CT/MA
to 05z eastern MA. Snow quickly becomes moderate to heavy at
times with snowfall rates of 1-2 inches possible at times from
about 04z to 10z west to east. Snow may mix with some sleet/ice
pellets and freezing rain after 09z. Mixing may include rain
across the islands after 09z. IFR will become common overnight,
with LIFR at times in heavier snow. Not much wind with this
event, generally 10 kt or less overnight.

Sunday...High Confidence in trends, some uncertainty how
departure of lingers snow bands.

Snow or mixed PL/FZDZ ends 09z-12z across CT and western MA.
Snow or a mix PF/FZDZ ends 12z-15z across RI and eastern MA
with a mix of rain possible south coast and islands. Very light
snow may linger along the eastern MA coast until 18z, then
improving conditions.

Snow totals for most terminals, 5-9 inches, but low probability
(10-20% chance) of 10-12" across northern MA terminals,
including KBOS.

Sunday night...high confidence.

VFR, dry weather and light winds. Thus, not expecting any
blowing/drifting snow.

KBOS TAF...High Confidence in TAF trends. Mainly snow event,
however, low probability (10-20% chance) of PL/FZDZ mixing in at
times after 09z Sunday. High confidence for 5-9" snow totals,
with a low prob (10-20%) of 10-12". Heaviest snow with 1-2"
hourly rates from about 04z-09z.

KBDL TAF...High Confidence in TAF trends. Snow may end as a mix
of snow/PL/FZ after 07z-08z. High probability for snow totals
5-9". Much improved conditions after 12z Sunday.

Outlook /Monday through Thursday/...

Monday: VFR. Breezy.

Monday Night through Tuesday: VFR.

Tuesday Night through Wednesday: VFR. Slight chance SN.

Wednesday Night: Mainly VFR, with local IFR possible. Breezy.
SN likely, FZRA likely.

Thursday: Mainly IFR, with local MVFR possible. Breezy. SN, PL,
RA likely, FZRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

     SMALL CRAFT ADVISORY LATE TONIGHT & SUNDAY...

Weak surface low emerges off the DE coast tonight and
intensifies slowly as it traverses along 40N and then across the
benchmark Sunday. This will yield east and then NNE winds 15-20
kt with gusts up to 25 kt. Snow and rain will limit vsby, but
improving Sunday afternoon from west to east.

Light winds and good vsby will be featured Sunday night.

Outlook /Monday through Thursday/...

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

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Tuesday: Winds less than 25 kt.

Tuesday Night: Winds less than 25 kt. Chance of snow. Local
visibility 1 nm or less.

Wednesday: Winds less than 25 kt. Slight chance of snow.

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of snow, rain likely, freezing rain
likely. Areas of visibility 1 to 3 nm.

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 10 ft. Rain likely,
freezing rain. Local visibility 1 nm or less.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Storm Warning until 1 PM EST Sunday for CTZ002>004.
MA...Winter Storm Warning until 1 PM EST Sunday for MAZ002>021-026.
     Winter Weather Advisory until 1 PM EST Sunday for MAZ022>024.
RI...Winter Storm Warning until 1 PM EST Sunday for RIZ001>007.
     Winter Weather Advisory until 1 PM EST Sunday for RIZ008.
MARINE...Small Craft Advisory from midnight tonight to 5 PM EST Sunday
     for ANZ231>235-237-250-251-254>256.

&&

SYNOPSIS...Nocera
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...EM/Mensch/FT
AVIATION...Dooley/Nocera
MARINE...Nocera