Winter Storm and Heavy Snow in Massachusetts, February 13, 2024

Area Forecast Discussion
National Weather Service Boston/Norton MA
134 AM EST Tue Feb 13 2024

.SYNOPSIS...

High pressure brings dry, tranquil weather with above normal
temperatures today. A quick hitting Winter Storm impacts the
region Tuesday. This brings heavy snow to portions of the
region, especially the southern half of southern New England, along
with strong to damaging winds for Cape Cod and the Islands.
Coastal flooding is likely Tuesday afternoon from Boston
southward to Cape Cod and the islands. Dry Wednesday and Thursday
with gusty northwest winds behind the system. A clipper system
will bring a quick shot of snow overnight Thursday into Friday.

&&

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

The southward trend continues with 00z NAM, HRRR, WRF-ARW and
WRF-NMM. Lowered accum north of the MA Pike where confidence is
highest in less snowfall. As a result converted some of the
warnings to advisories and dropped the advisory for NW MA. May
have to lower amounts further south but no changes made along
and south of the MA and will await full 00z model suite before
making any changes.

Key Points...

* Quick hitting Winter Storm Tuesday, though the trend has been less
  snow and quite a bit further south.

* Generally thinking the bullseye will be over southeast MA/southern
  RI where 6-10 inches is possible.

* Dangerous travel possible with widespread 1-2" per hour snowfall
  rates possible Tue AM through the afternoon.  May even have brief
  instances of 3" per hour rates.

* Wet snow & strong winds along the coast may result in power
  outages.

Details...

Well, I'll get right to the point with this update, there's been a
big change to the forecast this afternoon based on a remarkably late
but notable trend in the 12z/18z guidance which now keeps the bulk
of the snow centered over the south coast of southern New England.
This change is due not only to a southern shift in the track of the
low but also a notable shift in the 500 mb trough; with a slower and
less amplified solution and the northern and southern stream energy
failing to phase/strengthen as they pass through the region. This
shift has notably moved the zone of mid level frontogenesis to the
south, and since we typically see the best forcing/banding to the
northwest of the maxima this places southeast MA/Cape Cod and
southern RI in the bullseye. BUFKIT soundings do indicate decent
omega (forcing for lift) within the dendritic snow growth zone
further north into MA, so we should still see some decent snowfall
there, but the maxima looks to be south and east. While this is
remarkably late in the game for such a relatively big shift, nearly
all of the 12Z guidance including the 12Z ECMWF, 18Z NAM, 18Z HRRR
and more show it. The new forecast calls for a swath of 6 to 10
inches across southeast MA/RI with a pretty tight gradient to the
north down to potentially nothing in far northwest MA. Uncertainty
remains high, however, given marginal temperatures at onset (though
good dynamics should help cool the column to overcome this) and
potential for a shift back north with overnight guidance. This
southern shift brings slightly cooler air which may help mitigate
snow loading risk a bit, but a wet, and rather heavy snow continues
to be expected. Blizzard conditions are possible, especially on the
outer Cape where the strongest winds are expected, with gusts has
high as 55 mph possible. Elsewhere winds will be gusty, blowing 30-
40 mph over southeast MA and along the immediate coasts of MA and
RI. The Winter Storm Warning has been expanded into Cape Cod and the
islands while it has been downgraded to a Winter Weather Advisory
for western and north central MA.

The trough digs into Southern New England and lifts into the
Atlantic Tuesday afternoon with drier air quickly filling in no NW
flow. This brings snow to an end by 4 to 8 pm from west to east on
Tuesday evening.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...

Tuesday night will be much quieter with drier NW flow taking hold.
Winds will remain blustery, however given CAA and a well mixed
boundary layer. This will make lows in the low 20s feel more like
the low teens.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...

Highlights

* Dry Wednesday and Thursday with gusty winds

* Clipper system brings another quick round of snow Thursday night
  into Friday

Wednesday and Thursday

Upper level ridge and weak high pressure builds in behind Tuesdays
storm system allowing conditions to dry out and skies to clear
esspically with considerable dry air at the mid levels and aloft.
Highs on Wednesday and Thursday stay mild in the low to mid 30s.
With clear skies and new snowfall, opted to use cooler MOS guidance
dropping lows into the teens.  Winds remain gusty Wednesday out of
the NW due to a strong pressure gradient. Gusts of 25-35mph could
effect power restoration efforts inland while gusts of 30-40 knots
over the waters will likely lead to continued hazardous marine
conditions. Winds slowly begin to diminish Wednesday night into
Thursday but remain blustery at 10-15mph.

Thursday night into Friday

A clipper system brings a quick shot of snow Thursday night into
Friday along with more gusty winds. Deterministic and ensemble
guidance are in good agreement at this time on a clipper low
tracking through southern New England. Temperatures overnight should
remain below freezing allowing for the precip to fall all as snow.
The best chance for plowable snow looks to be across northern MA,
but could shift depending on the exact track of  the low. NBM 25th
to 75th percentile snow accumulations at this time range from 1-4
inches north of the MA pike, while south of the pike, snowfall
ranges from a coating to 3 inches. Snow looks to end Friday morning
with clearing skies Friday afternoon. Highs Friday top out in the
mid to upper 30s.

Gusty winds are likely again Friday as a strong 925mb LLJ of 40-50
knots moves over the region. Westerly winds will enhance mixing
which could allow for gusts of 35-45mph inland and 45-55mph near the
coasts. NBM shows low probabilities of 10-30% for gusts to exceed
46mph (Wind Advisory) inland esspically for the Berkshires. Over
Cape Cod and Islands, NBM probabilites are moderate to exceed 46mph
at 30-60%.

Saturday and Sunday

Another weak clipper system could affect the region Saturday, but
guidance at this time remains in disagreement on the track of this
next low. Winds remain breezy Saturday and Sunday with gusts of 10-
20mph. Highs both days top out in the low to mid 30s.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...

Forecast Confidence Levels:

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

Through 12Z...High confidence in trends moderate in timing.

VFR for much of the night with high clouds in place. Should see
the precip spreading in from SW to NE from roughly the 10-14Z
timeframe. During this period will see conditions deteriorate to
MVFR/IFR as snow spreads in across CT and much of interior MA.
RI and eastern MA starting off as rain or a rain/snow mix
initially. Light N/NNE winds increasing to 5-10 kts toward
daybreak and shifting to the NE.

Today...Moderate confidence.

Conditions continue to deteriorate to MVFR to LIFR conditions
with moderate to heavy snowfall. Precip across RI/eastern MA
initially rain or rain/snow. Should transition over to all snow
by roughly 14-16Z as intensity picks up. The only exception is
the Cape/Islands where could be as late as 16-18Z. Snowfall
heavy at times with 1-2" per hour snowfall rates accumulating
quickly from CT into RI and SE MA during the morning hours.
These heavier rates will be over SE MA including Cape Cod and
the Islands from 18-22Z. Worst conditions from roughly 14-18Z
inland and 16-22Z across the Cape/Islands. Winds out of the NE
at 15-30 kts shifting to the N/NNW during the afternoon. Gusts
of 25-50 kts. Highest speeds/gusts across the Cape/Islands.

Tonight...High confidence.

Snow tapers off roughly 21 to 02Z across eastern areas. Rapid
improvement to VFR. Winds out of the N/NW at 5-15 kts during the
evening shifting to the W late. Gusts diminishing rapidly across
the Cape/Islands from 25-35 kts around 00Z to 15-25 kts toward
06Z.

Wednesday...High confidence.

VFR with NW winds 15-25 kts. Winds gusting 25-35 kts.

KBOS TAF...Moderate confidence.

Rain spreads in by roughly 12-13Z. As precipitation intensity
picks up should see a change over to all snow by roughly 14-16Z.
Moderate to heavy snowfall from roughly 15-20Z. Still some
uncertainty on the northern extent of precipitation and snowfall
totals. At this point reasonably looks like roughly 3-6 inches
of snowfall. Improving to VFR roughly 23-01Z.

KBDL TAF...Moderate confidence.

Snow moves in around 10-11Z with conditions deteriorating
quickly with LIFR and moderate snow from 13-17Z. There remains
uncertainty on the northern extent of precipitation and snowfall
totals. At this point reasonably looking like 2-4 inches of
snow. Improving to VFR by roughly 20-22Z.

Outlook /Wednesday Night through Saturday/...

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

Thursday: VFR. Breezy. Chance SN.

Thursday Night: MVFR/IFR conditions possible. Strong winds with
gusts up to 40 kt. Chance SN, chance RA.

Friday: VFR. Strong winds with gusts up to 40 kt. Slight chance
SN.

Friday Night: VFR. Windy with gusts up to 35 kt.

Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance
SN.

&&

.MARINE...

Forecaster Confidence Levels:

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

Highlights...

* NNE winds increasing to between 40 and 55 knots Tue
* Gale & Storm Warnings In Effect with 10-15+ foot seas expected

Tonight...High confidence.

The weak high lifts further to the northeast and the pressure
gradient begins to tighten as our next system lifts off the Mid
Atlantic coast toward daybreak. Light winds during the evening
shifting to the ENE and increasing 15-30 kts after midnight.
Should see some 25-35 kt gusts toward daybreak.

Tuesday...High Confidence.

A rapidly intensifying low pressure passes near the Benchmark
on Tuesday. This system will under-go rapid intensification and
the pressure falls coupled with cold air aloft will aid in the
mixing process. Have upgraded Boston Harbor and Narragansett Bay
to Gale Warnings. Elsewhere the Storm and Gale Warnings still
look on track. Winds really ramp up during the day Tuesday
which will allow seas to build to between 10 to 15+ ft.

Tuesday night...High confidence.

Seas 6 to 9 ft. NW winds 15-20 kts gusting
25 to 30 kts.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Strong winds with gusts up to 40 kt. Rough
seas up to 11 ft. Chance of freezing spray.

Thursday: Low risk for Small Craft Advisory winds with local
gusts up to 30 kt. Local rough seas. Chance of snow.

Thursday Night: Low risk for gale force winds with gusts up to
40 kt. Areas of seas approaching 5 ft. Rain likely, chance of
snow. Areas of visibility 1 to 3 nm.

Friday: Moderate risk for gale force winds with gusts up to
40 kt. Areas of rough seas. Chance of snow.

Friday Night: Low risk for gale force winds with gusts up to
35 kt. Local rough seas.

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
snow, chance of rain.

&&

.TIDES/COASTAL FLOODING...
Key Points:

 - Coastal Flood Warning expanded to NE MA.
 - Widespread minor to moderate flooding during Tue PM high tide
   along E MA coast with significant beach erosion.
 - Residual minor flooding possible for early Wed AM high tide.

Fairly high confidence on widespread minor flooding (up to one foot
deep) with pockets of moderate flooding (1 to 3 feet deep) in more
vulnerable locations during Tue afternoon high tide along eastern MA
coast.

Little change from earlier thinking. Expecting a storm surge of 2 to
3 feet with higher values focused from Boston to Cape Cod Bay,
Nantucket, and Martha's Vineyard and somewhat lower values of around
2 feet closer to NH border. We continue to go slightly above model
storm surge guidance due to strong pressure falls and typical mode
bias. Likewise, wave mode guidance was increased by about 25% on
eastern MA waters which yields seas of 15-20 ft offshore.

We added northeast MA to the Coastal Flood Warning. Despite the
expectation of less surge, impacts will be higher than usual given
significant coastal erosion that has taken place this winter.

Finally, we should see some minor coastal flooding around high
tide earl Wed morning due to leftover surge and continued rough
seas. Flow is more N/NW by that time which could favor Cape Cod
Bay shoreline communities for most of the impacts. Coastal Flood
Advisories may be needed after we pass the Tue PM high tide
cycle.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Storm Warning until 1 AM EST Wednesday for CTZ002>004.
MA...Winter Storm Warning until 1 AM EST Wednesday for MAZ012>024.
     Winter Weather Advisory until 1 AM EST Wednesday for
     MAZ004>007-009>011-026.
     Coastal Flood Warning from noon today to 5 PM EST this
     afternoon for MAZ007-015-016-019-022>024.
     High Wind Warning from 7 AM this morning to 10 PM EST this
     evening for MAZ022>024.
RI...Winter Storm Warning until 1 AM EST Wednesday for RIZ001>008.
     Wind Advisory from 7 AM this morning to 7 PM EST this evening
     for RIZ008.
MARINE...Gale Warning from 7 AM this morning to 10 PM EST this evening
     for ANZ230-236.
     Storm Warning from 7 AM this morning to 10 PM EST this evening
     for ANZ231-232-254-255.
     Gale Warning from 7 AM this morning to 1 AM EST Wednesday for
     ANZ233>235-237-250-251-256.

&&

SYNOPSIS...BW/KP
NEAR TERM...KJC/BW
SHORT TERM...BW
LONG TERM...KP
AVIATION...KJC/BL
MARINE...BW/KP
TIDES/COASTAL FLOODING...JWD