BOX issues Area Forecast Discussion (AFD) at Jan 20, 10:22 PM EST773
FXUS61 KBOX 210322
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1022 PM EST Mon Jan 20 2025
.SYNOPSIS...
An arctic airmass will bring frigid conditions with minimum
wind chills on the order of 0 to 15 below zero at times through
Wednesday morning. Temperatures moderate a bit Thursday and
Friday, but they will remain below normal. Dry weather will
generally prevail the rest of this week...but will need to watch
a couple distant waves of low pressure in case they trend
further northwest.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
1015 PM update...
Winds have decoupled across much of the region as surface
ridging building in from the west. With fresh snowpack and
light winds temps have already fallen to lower single numbers
to near zero in the colder spots across interior MA. As a
result we lowered temps a bit with expected lows zero to -5F
across interior northern MA and possibly even a few degrees
colder in a few locations. Elsewhere lows zero to 10 above,
except teens outer Cape and Islands. Given lighter winds, wind
chill temps will not be as impacted as much as they could be,
but still expecting minimum wind chills zero to -10F away from
the south coast, with localized -10 to -15F wind chills over
higher elevations.
Previous discussion...
Key Message
* Bitter cold temperatures across southern New England tonight with
single digit low temperatures forecast across the region
* Cold Weather Advisory in effect for the north east slopes of
The Berkshires and northern Worcester County
Tonight
Gusty northwest winds this afternoon gradually diminish/decouple
after sunset. Clear skies, a fresh snow pack, and light winds should
support very efficient radiational cooling that will allow
temperatures to dip into the single digits for most of interior
southern New England. Some locations across interior MA at the
higher elevations may even approach 0. While winds will be on the
lighter side, there will be at least some mechanical mixing
that will limit a maximum radiational cooling effect, but
nonetheless wind chill temperatures will be well below 0 across
the interior overnight and into tomorrow morning. The coastal
locations will get some mild relief from the proximity to the
relatively warmer ocean, but will still experience single digit
wind chill values or lower.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Key Messages
* Bitter cold temperatures continue tomorrow and peak tomorrow night
* Cold weather headlines likely again tomorrow night
Tomorrow and Tomorrow Night
The arctic outbreak peaks tomorrow and tomorrow night as 925 hPa
temps continue to over at -15C or lower. Expect sunny skies across
the interior north of I-90 tomorrow, but across CT, RI, and
southeastern MA there will be increasing cloudiness as a plume of
moisture at 850 hPa edges over the region. High temperatures will
struggle to break out of the teens across the interior tomorrow, but
the coastal locations will be a bit more mild in the low to mid 20s.
Steady west/northwest winds from 10-15 mph will add a wind chill
factor that will have the day time temperatures feeling closer to
the single digits/low teens than the teens and low 20s.
After sunset, the atmosphere decouples allowing temperatures to
dip once again. Clouds over the southern half of the forecast
area retreat south and east and also may produce some light snow
over Nantucket/Marthat's Vineyard, but no substantial
accumulations would be expected. Areas with cloud cover to begin
with may not radiate as efficiently as they would otherwise on
a clear night, but clearer skies across the interior will
support the coldest temperatures during this stretch. Many
locations will have single digit or negative single digit
temperatures by Wednesday morning. With wind chill temperatures
well below -15F, for several locations west of I- 95, cold
weather headlines will likely be needed for a second night.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Key Messages:
* Bitterly cold Wednesday morning followed by highs that only reach
the lower 20s
* Single digit lows Wednesday night before temperatures begin to
moderate Thursday, although still expected to be below normal
* Dry throughout aside from some stray snow shower chances towards
the Cape Friday AM
Wednesday
An arctic airmass remains settled over the region before it begins
to make its exit Thursday. Temperatures at 850 mb Wednesday continue
to sit in the -25C to -20C range and forecast soundings indicate dry
conditions with good mixing, continuing this cold trend. Ensembles
show good probs for temperatures below 5F for Wednesday night
particularly across the interior and towards the Merrimack Valley.
Wind chill values Wed PM could once again reach the negatives in
some spots. Some mid to high level clouds could help keep
temperatures from sinking as low as they are expected to for Tuesday
night, but they continue to range from close to 0F to the low teens
as you move from the interior to the coast.
Thursday and Friday
A ridge of high pressure progresses east of the region by Thursday,
and milder air makes its way across southern New England.
Temperatures aloft are still low, but they improve to the -15C to -
10C range at 850 mb by the daytime hours. Highs are still expected
to be in the 20s and 30s for both Thurs and Fri, but it's an
improvement nonetheless. With the snowpack across much of the region
and clearer skies Thursday night, lows are still likely to tank into
the single digits and low teens outside of the Cape and Islands, as
they don't have as significant of a snowpack and may see more cloud
cover lingering during the overnight hours. Winds are expected to
remain light and mostly from the W to NW through both days.
The shortwave associated with the winter weather in the southern US
moves eastward Thursday night into Friday morning, however we're not
expecting any significant impacts at this time. At most, some stray
snow showers over the Cape could develop, but the signal in the
ensemble guidance still varies a bit at this point. The ECMWF
ensemble favors a drier solution while the Canadian is more
aggressive on the chance for some precipitation.
Saturday through Monday
Temperatures continue to moderate and dry conditions continue
through the weekend. Deep troughing over the SW US will encourage
geopotential heights to rise over the SE US. Ensemble height
anomalies also indicate height falls to our north and west, and an
area of low pressure to the N and NE with high pressure to the SW at
the surface is a favored outcome. So the difference between the
building heights in the south and the falling heights in the north
leading to this building pressure gradient at the surface will
encourage the development of slightly stronger W to SW winds over
the weekend with gusts up to 25 or 30 mph possible.
With the continued moderation of temperatures due to this SW flow,
highs Sunday are expected to be above freezing for much of the
region. Some spots could reach over 40F. Beyond this period, some
low precipitation chances show up for later Monday, but nothing
significant at this time.
&&
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00Z Update:
Tonight...High Confidence
VFR. Winds becoming WSW around 5 knots or less at most
terminals; slightly higher at Cape terminals and ACK.
Tomorrow...High Confidence
VFR. WSW to W winds around 10 knots. Increasing mid-level
cloudiness during the afternoon.
Tomorrow Night...High Confidence
VFR. Winds shift back to the northwest with speeds around 5
knots.
KBOS TAF...High Confidence in TAF.
KBDL TAF...High Confidence in TAF.
Outlook /Wednesday through Saturday/...
Wednesday: VFR. Breezy.
Wednesday Night through Friday Night: VFR.
Saturday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High- greater than 60 percent.
Tonight through Tomorrow Night
High confidence...
Small craft advisories remain in effect through tonight and
tomorrow for the outer marine zones. Arctic air mass settles in
tonight and persists through Wednesday supporting periods of
freezing spray. Winds will be relatively modest in the 10 to 20
knot range out of the west/northwest with some gusts up to 25
knots. Seas generally ranging from 2 to 4 feet.
Outlook /Wednesday through Saturday/...
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft.
Wednesday Night: Winds less than 25 kt.
Thursday through Thursday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. Slight chance of snow.
Friday through Friday Night: Winds less than 25 kt.
Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Cold Weather Advisory until 10 AM EST Tuesday for MAZ002-004-
008.
RI...None.
MARINE...Small Craft Advisory until 4 AM EST Tuesday for ANZ235-237.
Small Craft Advisory until 4 PM EST Tuesday for ANZ250-254>256.
Small Craft Advisory until 1 AM EST Tuesday for ANZ251.
&&
$$
SYNOPSIS...Frank/Mensch
NEAR TERM...KJC/RM
SHORT TERM...RM
LONG TERM...Hrencecin
AVIATION...Hrencecin/RM
MARINE...Hrencecin/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Jan 20, 10:22 PM EST----------------
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