Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 260943
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
443 AM EST Wed Jan 26 2022

.SYNOPSIS...
High pressure brings an arctic airmass into the region today 
and tonight. Not quite as cold Thursday afternoon along with 
less wind, but nonetheless remaining colder than normal. Then 
all eyes turn to a powerful coastal storm Friday night into 
Saturday night, which will likely impact at least a portion of 
the region with heavy snow, strong winds, coastal flooding and 
dangerous seas. However, still some uncertainty on the exact 
storm track and intensity, which will have a direct impact on 
snow amounts and other storm details. Drier weather returns with
below normal temperatures Sunday.

&&

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

330 AM update...

Today...

Arctic airmass slowly overspreads the region, on cold NNW drainage 
flow with 925 mb temps lowering to about -14C to -16C by days end. 
This strong low level cold air advection will preclude much if any 
temp rise from temps early this morning. Given this and shallow 
nature of the cold airmass, leaned toward the colder guidance 
sources to derive high temps today. This only yields highs in the 
low to mid 20s, upper teens for much of western-central MA. It will 
feel even colder in response to NNW winds 10 to 20 mph, highest 
winds over Cape Cod and the Islands.

&&

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

330 AM update...

Tonight...

Arctic 1030+ mb high builds into the region, yielding a cold night 
ahead with lows mainly ranging from -5 to +5 across much of the 
region. NNW winds will trend more northerly and diminish. Thus, not 
much of a wind chill overnight, nevertheless, very cold overnight. 
Given diminishing winds, mostly clear conditions and a very dry 
airmass, derived lows tonight from the colder MOS guidance. Before 
winds diminish, NNW winds trending northerly, very cold air on this 
trajectory over the relatively warm SSTs, will yield OES across the 
outer Cape and possibly into coastal Plymouth county.  The NSSL WRF 
and ARW are most aggressive with OES, and offer a coating up to an 
inch possible in spots across the outer Cape and coastal Plymouth 
county. This seems reasonable given 340 wind direction, delta-T of 
24 degs from top of the mixed layer (-18C) to SSTs of +6C, and very 
little directional shear in the boundary layer. Otherwise, dry 
weather prevails. 

Thursday... 

A very cold start to the day, but slight improvement as ridge axis 
aloft moves east of the region along with surface high sliding 
offshore, offering weak return warm advection flow to setup. Temps 
only a few degs higher than today, but light SSW winds and plenty of 
sunshine will help offset the colder than normal temps.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...

330 AM update...

Highlights...

* Light scattered snow showers possible on Friday with limited 
  accumulation. 

* A significant winter storm is becoming more likely for Saturday 
  with snow, strong winds, and coastal flooding all on the table. 
  Details will come more into focus over the next 24 to 36 hours. 

* Quiet weather to follow through early next week. 

Details...

Thursday night and Friday...

Thursday night high pressure shifts east of southern New England as 
a trough of low pressure traverses the Great Lakes and northern New 
England. Southernly flow ahead of the approaching cold front will 
bring increasing clouds through the overnight hours. 

By Friday these southwest winds continue, bringing temperatures 
several degrees warmer than on Thursday, into the mid to upper 30s. 
Expect a cloudy, mostly dry day but we'll see scattered snow showers 
thanks to the cold front and a favorably positioned 300 mb jet 
overhead; not expecting more than a dusting to several tenths from 
any of these showers. 

Friday night and Saturday...

1/26 00Z guidance continues to boost confidence that we're in store 
for a high impact winter storm in southern New England on Saturday. 
The ECMWF guidance is holding steady and all global guidance in 
agreement that some locations will experience a significant 
snowfall, strong winds, and coastal flooding. For those that have 
been following along, I know you've heard it repeated to death, but 
the key message continues to be the same: guidance is trending 
favorably for a big storm, but the exact track remains uncertain. 
This track is what will tell us exactly where the greatest snow, 
wind, and coastal flooding concerns are. 

The origin of this storm is a broad 500 mb trough that digs into the 
Ohio and Tennessee valleys Friday night into Saturday. Two shortwaves 
within the broader flow, one northern and one southern stream may 
phase with each other as they move east. The ECMWF continues to 
favor a phasing solution leading to a stronger mid level low which 
cuts off more quickly compared to the GFS which keeps these features 
more removed and leads to a low that deepens more slowly. Either 
way, there is a great deal of confidence that this trough will 
generate a surface low off the Carolina coast that will rapidly 
intensify as it moves up to New England. Guidance indicates 
potential for this storm to undergo bombogenesis, meaning its 
central pressure drops at least 24 mb in 24 hours. This creates a 
very tight pressure gradient, meaning strong, potentially damaging 
winds will accompany the snow. Bufkit soundings indicate potential 
for gusts to as much as 70 mph for the Cape and islands during the 
peak on Saturday. However, again the placement of heaviest winds, 
whether or not we deal with a rain/snow line, and extent of coastal 
flooding will be more clear as we approach and get a grasp of the 
track. Current ensemble guidance indicates a majority of the low 
centers passing in the vicinity of the 40/70 benchmark. If this 
comes to pass we'll be dealing with heavy snow over southeast MA, 
strong winds, and potential for white out conditions. 00Z EPS 
percentage possibility of a foot or more of snow continues to place 
a 60-70% bullseye over southeast Massachusetts. 

Finally, coastal flooding is a concern thanks to astronomically high 
tides on Saturday. The combination of strong northeast winds and 
high seas will bring storm surges that, if coinciding with high 
tide, would lead to minor or moderate coastal flooding. A difference 
in storm timing of as little as 6 hours would have a large impact on 
coastal flooding and erosion concerns. Stay tuned. 

Sunday through Tuesday...

By Sunday morning the low center will be north of Nova Scotia and 
lifting quickly away from New England. It is eventually replaced by 
high pressure later Sunday through Tuesday. During the transition on 
Sunday we'll continue to see gusty winds until the pressure gradient 
eventually slackens and winds become calm Sunday night through 
Tuesday. 

&&

.AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...
Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent.

06z update...

Today...High confidence 

VFR, dry weather and NW winds 10-20 kt, highest winds over Cape
Cod and the islands. Given this wind trajectory, ocean effect 
snow showers likely remain just offshore of Cape Cod. 

Tonight...High confidence. 

VFR, dry weather with NNW winds at 5-15 kts. Gusts up to 20 kts
across the Cape/Islands. This more northerly wind trajectory
likely results in ocean effect snow showers and MVFR conditions coming
onshore to Cape Cod and possibly coastal Plymouth county. A 
coating to an inch is possible. 

Thursday...High confidence. 

VFR, dry light and variable winds becoming SSW. Across the 
outer Cape, MVFR cigs and vsbys possible in morning ocean effect
snow showers.  

KBOS Terminal...High Confidence in TAF. 

KBDL Terminal...High Confidence in TAF.

Outlook /Thursday Night through Sunday/... 

Thursday Night: VFR. Breezy. 

Friday: Mainly VFR, with areas MVFR possible. Slight chance SN.

Friday Night: Mainly VFR, with local IFR possible. Windy with
gusts up to 35 kt. Chance SN.

Saturday: Mainly VFR, with areas MVFR possible. Strong winds
with gusts up to 60 kt. SN likely.

Saturday Night: Mainly VFR, with local MVFR possible. Strong
winds with gusts up to 45 kt. Chance SN.

Sunday: VFR. Windy with areas of gusts up to 30 kt. 

&&

.MARINE...
Forecaster Confidence Levels.

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

330 AM update...

Today...arctic high pressure approaches from the west, yielding NNW 
10-20 kt winds across MA and RI waters, along with light freezing 
spray. 

Tonight...arctic high continues building east into New England. More 
of a northerly wind 10-20 kt produces ocean effect snow showers over 
the eastern MA waters, along with light freezing spray. 

Thursday...high pressure moves offshore with light and variable 
winds becoming SSW wind and light, generally 15 kt or less. 

Outlook /Thursday Night through Sunday/...

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft. 

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain, slight chance of snow. 

Friday Night: Low risk for gale force winds with gusts up to
40 kt. Local rough seas. Snow likely, rain. 

Saturday: gale force winds with gusts up to 45 kt. Rough seas
up to 20 ft. Snow, rain. 

Saturday Night: Strong winds with areas of gusts up to 45 kt.
Rough seas up to 20 ft. Snow likely, chance of freezing spray. 

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 15 ft. Chance of freezing spray,
slight chance of snow. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 3 AM EST Thursday for ANZ250-254.

&&

$$
SYNOPSIS...Nocera/BW
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...BW
AVIATION...Nocera/BW
MARINE...Nocera/BW