Lexington Weather

Area Forecast Discussion
for Lexington, MA

        
000
FXUS61 KBOX 252332
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
632 PM EST Mon Jan 25 2021

.SYNOPSIS...
Dry and quiet weather tonight as high pressure remains in
control. A warm front lifts in and brings minor snow 
accumulation Tuesday night into Wednesday. This will result in
slick travel for parts of the region. Unsettled for midweek 
with considerable cloudiness and periods of ocean effect 
precipitation as a powerful low near the mid- Atlantic waters 
passes well to our south. Period of much below normal 
temperatures and low wind chills for late in the week, only 
gradually modifying into the weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

7 pm Update...

Forecast is on track with no changes necessary this evening. 
Temperatures were adjusted slightly to bring in line with 
observations, and timing of incoming cloud cover was slower a 
bit. 

Temperatures this evening are currently in the upper 20s and
will bottom out in the teens overnight. 

Previous Discussion...

Highlights

* Dry and quiet weather with increasing cloud cover. 

Ridge axis builds into the eastern Great Lakes tonight, but will
flatten out a bit as a trough lifts into Lower Michigan/Ohio 
Valley. A surface high will build into the region. 

Anticipate mid to high clouds to move in as low pressure deepens
over the Ohio Valley and warmer air advects in from south. Have
nudged down lows to the 15th percentile of guidance as there
should be good radiational cooling, but only crux will be how
quickly the clouds blanket the region. Lows range from teens
across the interior to the 20s along the coastal plain. There
will be a few locations across the higher elevation where
readings are in the single digits above zero.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/...
Highlights

* Winter Weather Advisory for the eastern slopes of the
  Berkshires and north central CT for light accumulating
  snowfall late on Tuesday into Wednesday. Snowfall totals of
  2-4 inches where the advisory is in effect. Light snow
  elsewhere with amounts in the 1-3 inch range.

* Light snow lingers on Wednesday, but coastal areas will see 
  some rain mixing in. 

Ridge axis builds offshore on Tuesday while a trough lifts into
the eastern Great Lakes. The trough moves into southern New
England by late Tuesday night and offshore early on Wednesday.
A surface low will lift across the eastern Great Lakes and
warmer air overspreads the region. Will see a secondary low
develop near the DE/NJ/VA area late on Tuesday and move
northeast well to the southeast of southern New England on
Wednesday. An inverted trough associated with this low will be
present on Wednesday lingering light precip. 

Dry to start across southern New England on Tuesday and it will
likely take a bit for precipitation to begin with a dry airmass
in place - dewpoints start out in the teens to single digits on
Tuesday. This will gradually moisten as winds shift from the 
north to the east advecting in marine air. Have tapered back 
precipitation chances, but don't think things will really get
going until the afternoon when the boundary layer is able to
moisten up per NAM/GFS BUFKIT soundings. This period of drier
air eroding is the best opportunity for any wintry mix, but
think this should be short lived and should be isolated to the
south coast per model soundings. 

Did trend the precipitation amounts upward as the 12Z suite of
guidance continues to the upward trend. This does tick up
snowfall amounts to around 3 inches into central MA. If the
upward trend continues will likely need to expand the Winter
Weather Advisory further east in future updates. As of right now
expect 1-3 inches of snow accumulation outside of the current
advisory with amounts closest to 3 inches central and portions
of western MA. Lesser amounts are anticipated elsewhere. Should
see the heaviest snowfall late on Tuesday into Tuesday night
before things wind down overnight into early Wednesday. Issued
the Winter Weather Advisory where am most confident in totals
falling in the 2-4 inch territory. Luckily for this event it
still does not appear that the snow growth region coincides with
the best omega. 

Inverted trough in place associated with the departing secondary
low on Wednesday. This will linger light snow showers across
much of southern New England on Wednesday, but expect coastal
areas to see some rain mixing in. Could potentially see a few
spots get an additional half inch of light snow across the
interior. Temperatures in the upper 20s to 30s on Tuesday and
30s to low 40s on Wednesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Wednesday Night: 

Persistent snow showers are likely across southern New England 
overnight Wednesday as an inverted trough trails across the area. 
Snow will be focused across southern New England, but may switch to 
rain across Cape Cod and the islands. 

Lows Wednesday night will range from the mid 20s in the west to mid 
30s across far eastern Massachusetts. 

Thursday: 

Snow chances diminish by daybreak Thursday as a high pressure system 
establishes itself over southern New England. A potent coastal low 
will track south of the region. Precipitation chances across 
southern New England are low considering high model consensus that 
the low will be centered off of the mid-atlantic. While this system 
will be a miss in terms of precipitation, winds will build from the 
NNE as the low moves off the coast into the Atlantic. Winds are 
likely to gust to 30 kts. The NNE wind will be accompanied by a 
region of enhanced moisture that may generate some ocean effect snow 
across Cape Cod, the islands, and the South Shore of Massachusetts. 
There remains a lower probability that these snow showers will 
expand to the I-95 corridor or even further. High temperatures 
Thursday will range from the mid to upper 30s.

Thursday Night into Friday Night: 

An area of colder than average air is pulled southward from Hudson 
Bay as the mid-Atlantic low pushes eastward. This pattern change 
will result in an extended period of much colder temperatures, as we 
trend well below average. Lows Thursday night will dip into the 
single digits and low teens. Gusty northwest winds, 15-20kts, will 
drop windchills below zero across most localities overnight 
Thursday. Worcester and points west may experience wind chills as 
low as -10F, but it is anticipated that values will remain above 
advisory criteria. Temperatures will struggle to climb into the mid 
to upper teens on Friday across the west, while eastern locations 
will climb into the low 20s. Increasing winds Friday, between 20-
30kts, will keep daytime apparent temperatures in the single digits. 

While winds begin to subside overnight Friday, cold temperatures 
remain in place. Widespread single digits are expected, except along 
the coast where temperatures remain in the teens. 

Saturday through Sunday:

With high pressure in place, the cold airmass will begin to loosen 
its grip on the region on Saturday, but temperatures will still 
remain about 10 degrees below average. Highs are expected to top out 
in the mid 20s. Saturday night will see temperatures drop again into 
the high single digits and low teens, however the subsiding wind 
will keep apparent temperatures 5-15 degrees above zero. 

On Sunday, temperatures rebound significantly, as still below 
average but more seasonable highs are expected, with upper 20s west 
and mid 30s south and east. 

The very cold air mass gradually modifies into the weekend, with 
high pressure remaining in control. This should support mainly dry 
weather into Sunday, though temperatures will still trend below-
average for late January.

Sunday Night through Monday:

High uncertainty remains about the timing of a potential coastal low 
Sunday night into Monday. Several models show consensus about the 
presence of the coastal low, but differ significantly with timing 
and evolution. The GFS shows that the system will begin push into 
the region on Sunday, while the European model suggests a much 
slower progression, with the bulk of precipitation approaching late 
Monday. As a result, temperatures, and QPF are hard to nail down 
late in the forecast and will be highly dependent on storm 
progression. More attention will be paid to this potential system as 
we approach the weekend.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels.

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

00Z Update...

Tonight... High confidence

VFR with light northwest to north winds. Mid to high clouds 
continuing to increase.

Tuesday...High confidence in trends moderate in timing

VFR for at least the first half of the day. Should gradually see
MVFR and possibly IFR conditions spreading in late in the
afternoon as snow spreads in from W to E. Light north winds
shifting to the E.

Tuesday night...Moderate confidence

MVFR to IFR with localized LIFR. Snow across southern New
England, may have some visibility reductions especially during
the evening where could be falling moderately into MVFR
visibility at times. Expect the intensity to come down after
midnight. 

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF. 

Outlook /Wednesday Night through Saturday/...

Wednesday: MVFR/IFR conditions possible. Chance SN, chance RA.

Wednesday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SHSN.

Thursday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHSN.

Thursday Night through Friday: VFR. Breezy.

&&

.MARINE...
Have continues Small Craft Advisories across the eastern waters
into this evening and late tonight. Will continue to see
northwest to north winds diminishing as high pressure builds in.
Should see waves fall below 5 ft late tonight.

Rain and snow spreads in Tuesday and Tuesday night and could
bring some visibility reductions. Winds shift from the N to the
E on Tuesday. Should see some 15-20 kt gusts across the southern
waters late on Tuesday and Tuesday night. Wave heights 2-4 ft.

Outlook /Wednesday Night through Saturday/...

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain. 

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers. 

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of rain showers. 

Thursday Night: Strong winds with local gusts up to 30 kt.
Rough seas up to 10 ft. Slight chance of snow showers. 

Friday: Strong winds with gusts up to 30 kt. Rough seas up to
11 ft. Slight chance of snow showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 1 PM Tuesday to 10 AM EST 
     Wednesday for CTZ002.
MA...Winter Weather Advisory from 1 PM Tuesday to 10 AM EST 
     Wednesday for MAZ002-008-009.
RI...None.
MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ231-
     251.
     Small Craft Advisory until 11 PM EST this evening for ANZ250.
     Small Craft Advisory until 2 AM EST Tuesday for ANZ254.

&&

$$
SYNOPSIS...BL/BW/KS
NEAR TERM...BL/BW/KS
SHORT TERM...BL
LONG TERM...BW/KS
AVIATION...BL/BW/KS
MARINE...BL/BW/KS