Lexington Weather

Lexington, Massachusetts, USA

14°F

1/23/2025 4:28am

Lexington Conditions: Overcast
Temperature: 14.2°F / -9.9°C
Dew Point: 5.5°F
Relative Humidity: 68%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.36 in Steady
Visibility: 10 miles
Snow Today: 0.0 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 200613
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
113 AM EST Mon Jan 20 2025

.SYNOPSIS...
A fast-moving low-pressure system will bring accumulating snow to 
the region tonight, with the most significant travel impacts 
occurring this evening between 7 pm - 12 am. An arctic 
airmass will bring frigid conditions with minimum wind chills on the 
order of 5 to 15 below zero at times Monday night through Thursday 
morning. Temperatures moderate a bit in the Thursday through 
Saturday time frame, but they will remain below normal. Dry weather 
will generally prevail, but a bit of light snow/flurries may clip 
the southeast New England coast late Tuesday night into Wednesday 
morning.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
920 PM Update...

* 1-2" Snowfall Rates through midnight-1 AM across much of
  eastern MA and RI with lighter snow thereafter

The rain/snow line continues to collapse southeast this evening
and was along and southeast of a Fall River to Hanover line.
We should see that changeover area move across the Cape Cod
Canal through 11 pm. Even the Cape should see a brief burst of
snow after midnight. 

The guidance continues to indicate very strong frontogenesis
just northwest of a backbent warm front at 850 mb. This will
result in 1-2" per hour snowfall rates across the Boston to
Providence corridor through midnight/1 am. While the heaviest of
the snow should be over by that time...another batch of lighter
snow will push through and should exit the coast between 4 
and 7 am. 

Temperatures will continue to tumble and be in the teens to the
lower 20s in most locations by daybreak. So even though the
accumulating snow will be over by the Mon AM commute...untreated
roads will be snow covered and slippery. 

We did not make any changes to the snow accumulations. This
looks to be a 3-6"/4-8" type of deal for many locations around
and northwest I-95. Even a few slushy inches are possible around
parts of Cape Cod. 

Previous Discussion...

Key Points

 *Winter Storm Headlines remain in effect for tonight
   *6-8 inches, with localized 10 inches NW of I-95
   *3-6 inches, with higher uncertainty SE of I-95 
   *0-2 inches across the Cape and the Islands

An area of low pressure strengthens as it makes a close pass 
offshore, with the center near the Cape and Islands. Model guidance 
remained consistent with this path today. Thus, confidence continues 
to increase for widespread accumulating snowfall across the region 
tonight. Precipitation moves in SW to NE tonight between 4 pm - 7 
pm, with a mix of rain/snow possible with onset due to above-
freezing temperatures around the region.  Temperatures should drop 
below freezing from NW to SE between 4 pm and 8 pm, allowing any 
rain-snow mix to change to snow.  

The heaviest snow and best potential for banding will occur between 
6 pm to 1 am, where 0.5 inch/hr snow rates are likely, with a low to 
moderate chance for 1-2 inch/hr snow rates.  The latest 12z Hi-res 
guidance favors SE of the I-95 corridor from Boston to Providence 
for the heaviest QPF and snow rates due to the close offshore track 
of the low.  However, SE MA and RI is the area of highest 
uncertainty because temperatures will take longer for temps to drop 
below freezing.  If temps stay above freezing after 7-8pm, then snow 
totals likely remain in the 3-6 range, but if they drop quicker, 
then 6-8 inches with localized 10 inches will be possible.  As for 
north and west of I-95, colder temps and higher snow-to-liquid 
ratios will make up for less QPF. Widespread of 6-8 inches is 
expected, with localized areas of up to 10 inches possible.  

As for the Cape and Islands, Temps should stay above freezing until 
after midnight; by this point, the heaviest QPF will have moved off 
to the northeast.  We did bump up snow totals with the slight shift 
south in the Hi-res guidance.  Expect anywhere from 0-2 inches, with 
localized 3-4 inches if colder temps move in quicker than expected. 

Winter storm warnings remain in effect north and west of the I-95 
corridor, with winter weather advisories SE of the I-95 Corridor 
except for the Cape and Islands. Snow ends from SW to NE tonight
between 1 am to 5 am, with some flurries lingering until 
sunrise. The most significant travel impacts will occur this 
evening as the heaviest snow occurs between 7 pm and midnight. 
Gusty winds behind the system could blow around snow, leading to
light travel concerns for the Monday morning commute.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
Key Points 

 *Arctic airmass brings wind chill values down into the single 
  digits on Monday 
 *Dangerously cold Monday night with lows around 0F

Arctic airmass moves in behind Sunday nights system with 850 MB 
temperatures crashing from -3C this afternoon to -20C by Monday 
evening.  With gusty winds around 15 to 25mph on Monday, the wind 
chill index (feels like temperature) will be in the single digits to 
low teens all day.  Winds begin to die down Monday evening and could 
go calm overnight as the boundary layer decouples.  Clear skies, 
calm winds, and sublimating snow will set up for strong radiational 
cooling and dangerously cold night.  Lows will likely bottom out 
near 0F, with wind chill values in the single digits below zero.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Key Points

* Arctic Outbreak Mon PM through Thu AM  
 -Minimum wind chills 5 to 15 below zero and perhaps as low as20
  in spots 
 -Actual low temperatures in the single digits, with some below
  zero 
 -Actual highs Tue and Wed mainly between 15 and 20

* Another offshore low pressure may impact southern New England Thu 
  night into Fri

Above average confidence in the forecast through Thursday. Latest 
guidance suite in rather good synoptic agreement with the deep mid 
level trough and surface high pressure. This will lead to an arctic 
outbreak across southern New England, with the coldest air we have 
seen so far this season. The peak of this cold looks to be 
Wednesday, with a very gradual warmup into Friday. Even then, 
temperatures still expected to remain below normal. Near normal 
temperatures possible this weekend. Much will depend upon the track 
of a low pressure late this week.

With the high pressure in place, not much chance for precipitation 
most of this week. The arctic air will generate some ocean-effect 
showers which will remain primarily over the coastal waters. Some 
chance they could back into portions of the outer Cape or Nantucket 
with a subtle wind shift, but that is a very low probability. 

The next low pressure which may impact our region looks to pass 
southeast of the 40N/70W benchmark towards Thursday night into 
Friday. We will likely need several more days to have a better idea 
of the risk posed by this particular system.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

Today...High Confidence.

IFR in -SN with periods of LIFR possible in any heavier snow 
bands that develop early this morning. One last round of light 
snow moves across from 06-10z. Conditions will improve to VFR by
daybreak Monday. Total snow accumulations of 3-6"(south and 
east)/4-8"(north and west) will be common for much of the region
northwest of the Cape Cod Canal.

NW winds with gusts of 20-25 kts possible today. Brief gusts to
30 kt possible across the Cape and at ORH. Winds decrease in the
afternoon to early evening. 

Tonight...High Confidence. 

VFR conditions with light west winds less than 10 kts. 

KBOS TAF...High Confidence in TAF. 

KBDL TAF...High Confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night through Thursday: VFR. 

Thursday Night: VFR. Slight chance SN.

Friday: VFR. 

&&

.MARINE...
Forecaster Confidence Levels:

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

High confidence...

increasing winds tonight to 15-20 kts with gusts to 30 kts as a
low pressure passes from southwest to northeast. Gusts up to 35
kts possible for the northern outer waters tonight through 
early Monday resulting in a Gale Warning. Otherwise, expect SCAs
generally through 12z Tuesday. Seas 4-9 ft. 

Outlook /Tuesday Night through Friday/...

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

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of snow showers. 

Wednesday Night through Thursday: Winds less than 25 kt. 

Thursday Night: Winds less than 25 kt. Slight chance of rain,
slight chance of snow. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Storm Warning until 7 AM EST this morning for 
     CTZ002>004.
MA...Winter Storm Warning until 7 AM EST this morning for 
     MAZ002>016-026.
     Winter Weather Advisory until 7 AM EST this morning for 
     MAZ017>021.
RI...Winter Storm Warning until 7 AM EST this morning for RIZ001-
     002.
     Winter Weather Advisory until 7 AM EST this morning for 
     RIZ003>007.
MARINE...Small Craft Advisory until 7 PM EST this evening for 
     ANZ230>234-236.
     Small Craft Advisory until 4 AM EST Tuesday for ANZ235-237.
     Gale Warning until 7 AM EST this morning for ANZ250.
     Small Craft Advisory until 1 AM EST Tuesday for ANZ251.
     Small Craft Advisory until 3 PM EST Tuesday for ANZ254>256.

&&

$$

SYNOPSIS...Belk/KP
NEAR TERM...Frank/KP
SHORT TERM...KP
LONG TERM...Belk
AVIATION...Frank/Mensch
MARINE...Belk/KP