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Area Forecast Discussion

Forecast Discussion for BOX NWS Office
FXUS61 KBOX 311122

Area Forecast Discussion
National Weather Service Boston/Norton MA
622 AM EST Tue Jan 31 2023

A slow moving cold front to move over the coastal waters this
morning. High pressure then governs conditions through Thursday
night, with seasonably chilly and dry weather. Dangerously cold
airmass arrives late Friday into Saturday, with widespread
below zero temperatures expected by Saturday morning. Some
ocean- effect snow showers are possible across Cape Cod.
Temperatures rebound quickly Sunday.



630 am update...

The front is making its way south and east, currently draped
across Cape Cod into our southern waters. Behind that, light
snow and rain showers continue to move east, mainly south and
east of a Hartford to Worcester to Lowell line. The main change
to the forecast with this update was to expand and extend POPs
in time for central/eastern MA and RI through 10am to 12pm.

Previous Discussion...

Early this morning, a cold front was draped across Mass Bay SW
through northern Providence County in RI into southeast CT. The
front`s SE egress is becoming increasingly slowed by front-
parallel low to midlevel SW flow. Modest SW flow ahead of this
front across south coastal MA/RI was contributing to areas of
mist with narrow T-Td spreads. Winds have flipped to NW in the
post-frontal environment, with considerable OVC along with
fairly disorganized and anafrontal light precip. Temps are
still warm enough that most of what is falling - and it is quite
light - is light rain showers; however shallow cold air lurks
behind the front across NH/ME and into eastern NY with light
snow (visbys no worse than 2 statute miles).

So for today, the aforementioned cold front will continue to
trudge SE towards the southern coast; there is some indication
in the 00z NAM/GFS and some of the CAMs that precip may expand a
bit in covg as it reaches the southern coastline into the mid-
morning hrs. But most of what falls should be in the form of
rain showers, though ending as brief period of snowflakes/light
snow showers. There just isn`t enough lifting and the column
cooling occurs too late to generate much of any snow
accumulation (and that which does would be on grass given the
paltry precip rates not overcoming mild pavement). While the day
begins generally OVC, some opportunity for cloud breaks should
ensue toward more of a mix of clouds and sun in the post-
frontal air, eventually reaching the southern coast by the
afternoon. Cold advection should lead to hovering or slowly
falling temps especially this aftn, offset by what diurnal
heating we do get. Cold advection drives 925mb temps -8 to -12C
by late-day, which will also help to produce occasional gusts
20-25 mph in the interior. Highs in most locations, especially
along and ahead of the front, likely have already occurred in
the mid 30s-low 40s. Afternoon temps should range from the mid
to upper 20s to the mid 30s.


245 AM Update:


Fairly energetic WSW 500 mb flow still governs conditions across
SNE, even as a 1028 mb sfc anticyclone ridges into NH/ME. Brief
period of generally clear skies should permit good radiational
cooling at least for a few to several hrs tonight. The challenge is
on how low temperatures get as another poorly-defined shortwave
embedded in the WSW flow aloft - essentially marked by a 500 mb
speed maxima of 90-100 kt - results in a west to east increase in
what looks to be a layer of mid-level clouds. In addition, we may
have some periodic streets of ocean effect stratocu near Cape Cod as
the colder air flows over the warmer ocean waters on N/NE flow.
Given 925 mb temps -10 to -13C and PWATs tumbling to 0.15 to 0.3
inches, there is plenty of room to radiate lower than the current
forecast shows, which adds some uncertainty to lows and potential
for busting too high; thinking stronger radiational cooling then
either slows or is halted as midlevel clouds increase towards OVC.
There is some moisture which advects NE towards our southern coastal
areas early in the morning, hinted at most aggressively by the NAM-
3km, FV3 and the SREF mean; just don`t see this as realistic given
drier northerly flow and confluent mid-level height pattern, each of
which should this suppressed by drier low-level air. Lows in single
digits NW MA with mid-teens to lower 20s elsewhere.


Should see decreasing clouds toward mostly clear skies on the first
day of February 2023; this occurring as sfc ridge builds across CT-
RI and SE MA into our coastal waters. Modest west winds, mostly full
sun for most of the day and neutral to slight warm advection to
boost highs in the upper 20s to the mid 30s, around or slightly
cooler than average.



* Seasonably cold on Thursday before a shot of dangerously cold air
  arrives Friday into Saturday.

* Much warmer air arrives for Sunday and Monday


Wednesday night and Thursday...

Quiet and dry weather is expected through Thursday as high pressure
builds in from the Mid-Atlantic overnight into the first half of
Thursday. Thus, under the influence of high pressure overnight we
may have a good night of radiational cooling if clouds can stay away
long enough for winds to decouple; have mixed in MOS guidance to
account for these colder temps, into the teens overnight. By
Thursday 850 mb temps previously around -12C will rebound to around -
5C on warm SW flow ahead of an approaching trough. This will
translate to high temperatures right around normal for early
February, in the upper 30s.

Friday and Saturday...

Don`t get used to those seasonable temperatures, because they aren`t
around for long. A dangerously cold airmass will be on our doorstep
early on Friday as a deep trough digging into the eastern seaboard
will deliver a shot of pure arctic air, the likes of which we
haven`t seen in years (Valentine`s Day of 2016 being the last time
we saw cold of this magnitude). The arctic front delivering this
cold shot arrives sometime Friday morning, likely as early as the
pre-dawn hours for western zones. Though guidance is coming into
more agreement on the arrival time, there remains some uncertainty,
and the core of the cold air doesn`t arrive until Friday night/early
Saturday. This means that Friday`s high temperature will occur
during the early hours of the morning before the strong cold air
advection takes place. The core of cold air is an airmass with 850
mb temperatures off the charts cold (climatologically), in the -30
to -35 F range. At the surface this will translate to low
temperatures of -5 to -15 F, potentially as low as -20F  in the
highest elevations of the Berkshires. There remains a decent gap in
forecast temps between the GFS (warmer) and ECMWF (colder) but both
are forecasting dangerous cold and it is supported by ensemble
guidance. The most concerning aspect will be the wind chills of -20
to -40 F overnight thanks to very strong winds that will coincide
with the coldest air. Fortunately this shot of cold air is
progressive given the lack of blocking downstream, so heights will
already be rising on Saturday. The other concern given the cold air
and strong winds will be for freezing spray for mariners Friday and

Sunday and Monday...

As previously mentioned temperatures will very quickly moderate with
mid level ridging moving back overhead early Sunday and warm SW flow
kicking in. This sends temps back well into the 40s Sunday and
Monday ahead of a passing shortwave. This shortwave may bring about
some showers on Sunday, but confidence is low that we`ll have enough
moisture and forcing to see any precip out of it.


Forecaster Confidence Levels:

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

12Z TAF Update:

Today: High confidence.

MVFR ceilings for Cape Cod and the Islands with possible light
shra thru the AM hrs. Little if any accumulation expected.
Elsewhere SCT- BKN VFR ceilings. NW winds increase to around
9-13 kt, with occasional gusts 18-20 kt early to mid-AM thru

Tonight: High confidence.

VFR, as a weak/fast-moving disturbance aloft increases covg of
midlevel clouds after ~05z. Streets of lower-VFR ocean effect
stratocu across the Outer Cape but away from HYA/ACK. Wind
speeds decrease to 4-8 kt (calm at times in interior late) with
a gradual veer from NW thru N/NE.

Wednesday: High confidence.

Decreasing clouds for most toward VFR SKC; however lower-
VFR/possible MVFR ocean effect stratocu could affect Cape Cod
thru the morning before trending VFR. Light N/NE winds become W
4-8 kt.

KBOS Terminal...High confidence in TAF. Spotty light -SHRA with
MVFR ceilings thru about 11z, then trending dry. Period of NW
gusts around 20 kt may start around ~15z.

KBDL Terminal...High confidence in TAF. MVFR ceilings improve to
VFR around 10-11z.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: VFR.

Thursday: VFR. Breezy.

Thursday Night through Friday: VFR. Strong winds with local
gusts up to 40 kt.

Friday Night: VFR. Strong winds with gusts up to 40 kt.

Saturday: VFR. Strong winds with local gusts up to 40 kt.


Forecaster Confidence Levels:

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

245 AM Update:

Overall high confidence.

Largely tranquil and sub-SCA marine conditions to prevail
through Wednesday.

A cold front will cross into the waters early today, bringing
initial SW winds to NW near most of the southern waters with gusts
15 to 20 kt. Seas mainly 2-4 ft. Spotty light showers of rain or
snow but visbys should not be too restrictive (above 4 miles).

Winds become light N/NE tonight, with possible light snow showers
along the far southern offshore waters late overnight to early Wed.
Winds become light W on Wed with gusts around 10 kt.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt.

Thursday: Low risk for Small Craft Advisory winds with local
gusts up to 30 kt. Seas locally approaching 5 ft.

Thursday Night: Strong winds with gusts up to 35 kt. Seas up to
5 ft.

Friday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 10 ft. Chance of freezing spray.

Friday Night: Moderate risk for gale force winds with gusts up
to 45 kt. Rough seas up to 10 ft. Chance of freezing spray,
chance of snow.

Saturday: Moderate risk for gale force winds with gusts up to
40 kt. Areas of rough seas. Chance of freezing spray, slight
chance of snow.


Record Low Temps Sat Feb 4...

Boston-2 in 1886
Hartford    -8 in 1965
Providence  -2 in 1918
Worcester   -4 in 1934

Record Low Maximum Temps Sat Feb 4...

Boston      11 in 1886
Hartford    12 in 1996
Providence  13 in 1996
Worcester    8 in 1908




NEAR TERM...Loconto/BW
SHORT TERM...Loconto

NWS BOX Office Area Forecast Discussion


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