Area Forecast Discussion
National Weather Service Boston/Norton MA
644 AM EST Sat Jan 29 2022

.SYNOPSIS...
A powerful winter storm with near record snowfall, blizzard 
conditions, near hurricane force wind gusts and coastal flooding 
will impact much of southern New England Saturday into Saturday 
evening. Drier weather returns with below normal temperatures Sunday 
before a warm up next week.

&&

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

645 AM update...

Very impressive satellite imagery this morning, with half 
wavelength shortening between trough and downstream ridge, as 
trough begins to take on a negative tilt. 

Forecast remains on track, with moderate snow overspreading
eastern CT-RI and eastern MA, with snowfall rates approaching 1
inch per hour. Winds have really cranked upward the past hour,
with PVC G50 kt/58 mph the past hour! Still expecting the
heaviest snow with hourly rates of 2-4" per hour at times along
with strongest winds up to 65-75 mph between 9 am and 4 pm. 

Rain has flipped over to all snow now across Nantucket and the
outer Cape. Although this will be a heavy wet snow, including
coastal Plymouth county and increase the threat of tree damage
and power outages. Earlier discussion below.

===================================================================

*** Powerful multi facet winter storm w/near record snow, blizzard 
conditions, near hurricane force wind gusts & coastal flooding ***

Highlights...

* Near record snowfall with a widespread 1 to 2 ft snowfall in 
  eastern MA & RI, along with blizzard conditions. Localized amounts 
  up to 3 ft possible in this region
 
* Snowfall rates could reach 2 to 4 inches per hour at times with 
  possibility of thundersnow across eastern MA and RI. This will 
  make travel very dangerous to nearly impossible
 
* Near hurricane force wind gusts are possible along the eastern MA 
  coast, possibly resulting in power outages 

Overview...

Explosive cyclogenesis underway with surface low down to about 989 
mb at 09z east of the DE coast. Mid/upper level trough amplification 
evident on satellite, with negative tilt and cooling cloud tops, 
along with a classic baroclinic leaf signature. This will support 
rapid deepening today and into this evening, with 00z guidance 
indicating a sub 970 mb low just off the eastern MA coast at 00z 
Sunday! This will be about a 35 mb pressure drop in 24 hrs, from 00z 
Sat to 00z Sun! Hence, meeting and surpassing bomb cyclone criteria. 

Details...

Near record snowfall/extreme snowfall rates...

00z models have trended slightly farther west with qpf and slightly 
heavier as well. Given storm intensity and rapid amplification along 
with mid level low track over or just east of the eastern MA coast, 
this trend seems reasonable. Very strong jet dynamics which includes 
a dual upper level jet streak, combined with a moist/cold NE 
conveyor belt up to 80 kt off the Atlantic into SNE, will provide a 
firehose of abundant moisture, supporting a period of very heavy 
snowfall from approximately 9 am to 4 pm. In addition, as dry slot 
approaches eastern MA and RI this afternoon, model soundings 
indicate a potential moist absolute unstable layer (MAUL) in this 
area. This seems reasonable as approaching dry slot will help 
steepen mid level lapse rates. All of the attributes listed above 
support intense snowfall rates of 2-4" per hour at times, along with 
thundersnow. Also, model/BUFKIT time sections indicate the bulk of 
the lift is occurring in the snow growth region later this morning 
and afternoon. This will yield SLR of 15-20 to 1. Therefore, an 
upward trend in qpf, a shift slightly farther west and heavy snow 
bands with high SLR, have resulted in slightly higher snow totals 
from previous forecast, and slightly shifted west. Heaviest snow 
(near record snow possible) will occur across RI into the Worcester 
Hills, with 18-24" likely. In eastern MA, 24-30" is likely. These 
higher totals in RI and the Worcester Hills will hinge on mesoscale 
banding pivoting westward from eastern MA into RI & the Worcester 
Hills. 

These snow totals will be record or near record in many locations. 
In addition, strong NE winds will result in snow drifts up to 4 ft 
and possibly higher. Considerable blow and drifting along with near 
zero vsby at times, will result in very dangerous to impossible 
travel conditions late this morning and afternoon. In addition, with 
temps falling through the teens and WCI at or below zero, this will 
be a very dangerous situation for anyone becoming stranded on the 
roads. Hence, don't venture out if at all possible because it could 
become a life-threatening situation.

Snow totals will decrease westward across CT (especially CT River 
Valley westward) and west of the Worcester Hills in MA. Our snow 
totals in northwest MA may have to be adjusted downward, as some 
concern very cold/dry air advecting into that region (KAQW dew pt 
currently 2F) may overwhelm the boundary layer, resulting in less 
snowfall. Something we will be monitoring. 

PTYPE and Snow Load...

Well defined coastal front already established, with north wind at 
KBOS with a temp of 27F. Meanwhile, KGHG northeast wind and 34F. As 
strong pressure falls approach from the south, this coastal front 
will become more pronounced and begin to bleed southward. These 
pressure falls will also cause rain early this morning across the 
outer Cape and Nantucket, to flip over to snow between 7 am and 10 
pm, as winds shift to the NNE and draws colder air southward. The 
concern here is that there could be many hours of wet snow here, 
increasing the weight of tree branches and limbs. This combined with 
NE winds gusting as high as 65-75 mph from about 9 am to 4 pm, will 
increase the risk of tree damage and power outages across Nantucket, 
Cape Cod and possibly coastal Plymouth county. This delay in 
changeover from rain to snow, will reduce snow totals to 12" to 18" 
across the outer Cape and Nantucket.

Strong to Damaging winds...

As mentioned above, anomalous low level NE jet combined with steep 
low level lapse rates, NNE winds 30-40 mph with gusts up to 65-75 
across Cape Cod and the Islands, including Cape Ann, will increase 
the risk of tree damage and power outages. The greatest risk could 
be across Cape Cod, the islands and coastal Plymouth county, as 
heavy wet snow combines with these strong/damaging winds. In 
addition, these very strong winds combined with snowfall rates of 2-
4" per hour at times, will yield blizzard conditions across RI and 
eastern MA, with vsbys near zero at times. Even after the snow 
tapers off early this evening, there will continue to be 
considerable blowing and drifting snow. 

Coastal flooding...

See coastal flooding section for discussion.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...

5 AM update...

Intense cyclone pulls away with snow tapering off this evening. 
However strong and gusty NNW winds will result in considerable 
blowing and drifting snow. Very cold night with deep fresh snow 
cover supporting lows in the single digits for most location. Gusty 
NNW winds will combine with cold temps to yield WCI from zero to 
minus 15! Dangerous conditions to be outdoors.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...

5 AM update...

Highlights...

* Quiet and increasingly mild weather to follow through much of the 
  week. 

* Rain returns Thursday into Friday

Details...

Sunday and Monday...

A trough east / ridge west pattern continues late weekend and early 
in the week while a ridge of high pressure moves in at the surface. 
Initial NW mid level flow will bring 850 mb temps down near -15 C on 
Sunday making for a cold day with highs only in the low to mid 20s; 
fresh snow cover, though, might keep highs a few degrees lower than 
that. This, together with breezy winds thanks to the lingering tight 
pressure gradient means it will feel more like the single digits and 
low teens. Wind gusts to 25 to 35 mph over the water and the cold 
temperatures will also lead to freezing spray issues. A Freezing 
Spray Advisory is in effect Sunday morning. By Monday that steering 
flow becomes more westerly advecting marginally warmer and more 
moist air into southern New England. Skies will be clear on Sunday 
with a mix of clouds and sun on Monday thanks to that increase in 
moisture. 

Tuesday through Friday...

High pressure moves overhead on Tuesday with an mid level ridge axis 
and warming temperatures before our next chance of wet weather on 
Wednesday. This as a low passes to our north over the Great Lakes 
and northern New England pulling a warm front north across the 
region early Wednesday. This brings much milder temperatures with 
it, in the mid 40s Wednesday and near 50 Thursday, along with 
scattered rain chances on Wednesday. The cold front hangs up to our 
west, keeping the region beneath moist southwest flow through at 
least Thursday. PWATs surge over one inch on Thursday ahead of the 
cold front and incoming mid level trough. Forcing from the trough, 
cold front, and right rear quadrant of a 150 kt upper jet will work 
together with all that moisture to bring a soaking rain around 
Thursday or early Friday. Too soon for details like timing, whether 
it turns to snow on the back side, etc but this could be a decent 
slug of rain.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent.

12z update...high confidence on trends, lower on exact 
details/timing

No change to previous TAFs, heaviest snow & strongest winds
14z-21z. Earlier discussion below.

=================================================================

*** Blizzard conditions much of the day, especially 14z-21z
 across RI and eastern MA, including Cape Cod, MVY & BID ***

Heavy snow and strong NNE winds will produce blizzard conditions
in RI and eastern MA from roughly 14z-21z, with IFR/LIFR
conditions, along with considerable blowing and drifting snow.
Conditions not as severe westward into CT and western MA. 

Snow totals by 7 pm Saturday...

KBOS...18-24" with higher drifts
KPVD...15-20" with higher drifts 
KORH...10-16" with higher drifts 
KBDL...6-10"

Tonight...high confidence.

At 00z, any lingering moderate snow in IFR conditions will
improve steadily during the evening as the snow shield exits
into northern New England. Trends will be for MVFR and
eventually VFR toward morning. However, gusty NNW winds and
dry/fluffy snow will result in considerable blowing and drifting
snow. Thus, even after snow ends, snow will likely blow back 
onto runways.

KBOS Terminal...heaviest snow with possibly 2-4" hourly 
snowfall rates along with strongest winds 14z through 21z Sat.

KBDL Terminal...heaviest snow with possibly 1-2" hourly snowfall
rates and strongest winds 14z through 20z Sat. 

Outlook /Sunday through Wednesday/... 

Sunday: VFR. Windy with local gusts up to 30 kt. 

Sunday Night: VFR. Breezy. 

Monday through Tuesday: VFR. 

Tuesday Night: Mainly VFR, with local IFR possible. 

Wednesday: VFR. Slight chance RA.

&&

.MARINE...
Forecaster Confidence Levels.

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

5 AM update...

** Storm Warnings with near hurricane force gusts today **

Powerful Nor'Easter will continue to advance NE toward the Gulf of 
Maine this afternoon and produce dangerous conditions for mariners. 
NE wind gusts increase to 55-60 kt on most waters, with with NE 65-
kt gusts by Saturday early afternoon with potential for gusts at 
times to near hurricane force on the eastern outer waters. Seas 
build to 15-20 ft on the southern waters, and 20-30 ft by this 
afternoon on the eastern waters. 

Areas of snow will reduce visibility to near zero at times, and 
accretion of freezing spray late this afternoon on vessel masts 
could also make for difficult navigation.

Tonight: High confidence. 

Powerful Nor'easter will continue to pull away NE into Atlantic 
Canada through the overnight. 

NW storm-force gusts should continue through about midnight, then 
become around gale force (35-40 kt) for the overnight. Seas will 
tend to decrease though some initial 20-25 footers still possible 
thru midnight on the eastern offshore waters. By daybreak, expect 
seas 6-10 ft on the southern waters, and 9-12 ft with increasing 
period. Risk for freezing spray will continue, with improving 
visibility as snow tapers off/shifts NE. 

Outlook /Sunday through Wednesday/...

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 13 ft. Freezing spray. 

Sunday Night: Winds less than 25 kt. Local rough seas. 

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

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

Tuesday Night through Wednesday: Winds less than 25 kt. Seas up
to 5 ft.

&&

.TIDES/COASTAL FLOODING...
5 AM update...

*** Coastal Flood Warning for this morning's high tide ***

Given earlier arrival of strong winds and storm surge, decided to 
hoist a coastal flood warning for this morning's high tide. 
Expecting storm surge of 2.0-2.5 ft combined with building waves on 
top of this surge. Seas offshore will be 15-20 ft at the time of 
high tide. This combination should support areas of moderate 
flooding especially from Nantucket northward along the Plymouth 
county coast. Slightly lower confidence northward to Boston, Cape 
Ann, but high enough risk to include in the warning. For Boston, 
expecting a total water level of around 12.5 ft with 15-20 ft seas 
offshore.  For Nantucket, total water level of 6.0-6.5 ft with waves 
7-10 ft in the harbor. 

Still expecting minor coastal flooding with this evening's high 
tide, thus have kept the coastal flood advisory in effect for this 
evening.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Storm Warning until midnight EST tonight for CTZ002>004.
MA...Blizzard Warning until midnight EST tonight for MAZ005-006-013-
     014-017-018-020-021.
     Coastal Flood Warning until 11 AM EST this morning for MAZ007-
     015-016-019-022>024.
     Coastal Flood Advisory from 7 PM this evening to midnight EST 
     tonight for MAZ007-015-016-019-022>024.
     Blizzard Warning until 5 AM EST Sunday for MAZ007-015-016-019-
     022-023.
     Winter Storm Warning until midnight EST tonight for MAZ003-004-
     008>012-024-026.
     Winter Weather Advisory until midnight EST tonight for MAZ002.
RI...Blizzard Warning until midnight EST tonight for RIZ001>008.
MARINE...Storm Warning until midnight EST tonight for ANZ230>237-250-
     251-254>256.
     Freezing Spray Advisory from 4 PM this afternoon to noon EST 
     Sunday for ANZ231>235-237-250-251-254>256.

&&