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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 292033
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
333 PM EST Sun Jan 29 2023

.SYNOPSIS...
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Low pressure passes to our north tonight, bringing enhanced
cloud cover and continued mild nighttime lows tonight. A spot
shower or two are possible mainly in eastern and southeast New
England. Another weak frontal system moves across later on
Monday, with arrival of more seasonable air Monday night. Quiet
with near seasonable temps for the middle portion of the work
week as a few precipitation makers are suppressed to our south.
Brutally cold airmass arrives for a 24 hour period late Friday
into Saturday with the potential to drop temperatures below
zero; chance for some ocean effect snow showers across the Cape
Saturday as well. Temperatures rebound quickly for the second
half of the weekend.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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315 PM Update:

Mild Sunday afternoon across Southern New England, with current
temps in the mid 40s to mid 50s. However mostly cloudy skies (of
largely mid-level cloud cover) along with modest south breezes also
are in place, associated wth a broad warm sector associated with a
weak sfc wave low pressure near Toronto ON. Regional radar mosaic
shows some echoes being returned but dry air below cloud base is
keeping these rain showers from reaching the ground.

For tonight, the weak surface wave low pressure area moves NE along
the St. Lawrence River Valley in adjacent far northern NY/VT and
into adjacent northern NH/ME. Its surface cool front/trough to
traverse across Southern New England early tonight, reaching the
offshore waters during the overnight. Model soundings show dry air
between 900-800 mb not fully saturating up enough to allow for
steady rain to develop; if anything were to reach the ground it
would amount to sprinkles with dry pavement/sidewalks. While there
is a fairly good 925 mb SW jet of 35-40 kt across eastern and
southeast MA, with shallow mixing progged, gusts across Cape Ann and
SE MA/Cape Cod and the Islands probably won`t get any higher than 30
mph and 20-25 mph gusts should be more common. While the weak cold
front will shift winds to the west with lowered speeds late, it
won`t be enough to allow for the leading edge of more colder air
across the Gt Lakes to advect NW. In fact should again be a
fairly mild night. Other than across the Berkshires where lows
in the upper 20s to near freezing should be common, elsewhere
lows should be in the mid 30s to low 40s as cloud cover and
neutral thermal advection takes place.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
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315 PM Update:

Monday is close to a facsimile of Sunday, with another sheared-out
vort 500 mb vort max and weak surface low to move across SNE.
Similar to Sunday as well, the front looks to again suffer from a
poorly-saturated column but may be a little more in support of light
rain showers (amounting to no more than a couple hundreths, again
roads/sidewalks mostly dry vs wet). Light west winds to become south
in the pre-frontal environment. Increasing clouds, and highs may be
a touch cooler than today but generally in the 40s, perhaps a spot
50F for eastern CT, RI and SE MA.

Front clears off the coast early on Monday night; winds to shift to
the NW and increase to around 15-20 mph. Despite still a fair amount
of post-frontal cloud cover, sharp if shallow cold advection takes
place with 925 mb temps fall from 0 to +3C by early Monday evening
to -1 to -8C by Tuesday early morning. Some decrease in clouds
toward morning but all in all a mostly cloudy evening with lows in
the upper teens to mid 20s across NW MA, upper 20s to around 30 for
Hartford to Worcester metros NE to the North Shore, and around
freezing to mid 30s eastern/southeast MA and RI.
-- End Changed Discussion --

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Highlights

* Generally quiet and seasonably mid week

* High confidence in a short lived cold snap late Friday and early
  Saturday that will bring sub-zero temperatures to portions of our
  region

* Temperatures rebound for the second half of the weekend


Tuesday through Thursday...

Given we are in the midst of the most climatologically active period
of the year for winter weather, between now and mid February, the
long term is looking eerily quiet in terms of appreciable snowfall.

Temperatures return to climatological means for the better part of
the work week given a generally zonal mid level flow pattern.
Guidance continues to suppress a weak precipitation maker to our
south late Tuesday through Wednesday as a broad area of high
pressure parks itself between the Ohio River Valley and New England.
At best, expecting the impact from this system to be restricted to
some light rain or snow showers along the south coast on Wednesday,
with little to no appreciable precipitation. A second low tracking
across the mid-Atlantic Thursday also appears to be shunted to our
south.

Friday and Saturday...

The most interesting part of the long term period comes late Friday
through Saturday morning as a very quick blast of arctic air makes
its way into New England. With a strong 1050mb high across northern
NY and southern Quebec, there is growing confidence in a significant
cold airmass with 850 mb temperatures dropping between -30 and -
40C, and yes you read that right, BELOW zero. In addition tthe
raw GFS and ECMWF coming into agreement about these bone
chilling temperatures, ensembles show high probabilities,
between 60-70% chance, of surface temperature dropping to 30
degrees below normal. For this time of year, an anomaly of
-30F drops overnight lows below zero, and daytime highs in the
upper single digits. Went with the NBM during the period, but
if current trends in the GFS and ECMWF verify, there will be
significant wiggle room in the lower bound of temperatures; the
12Z ECMWF currently diagnoses a low of -12F in Boston Saturday
morning. Fortunately, this blast of cold air will be quick
hitting, with the brunt of the impact expected between about
00Z-18Z Saturday before much warmer temperatures advect into our
region. For reference,it is possibly that temps could rival
those that occurred Valentine`s Weekend of 2016.

Cold temperatures will be amplified by gusty NW winds driven by
strong CAA, dropping apparent temperatures to -20 to 30F overnight
Friday into early Saturday. While we do not currently have a wind
chill watch in place, it is very likely that one will be hoisted in
the coming days given growing confidence in this high impact cold
event. As an early notice, southern New Englanders should consider
taking action to prepare for this shot of cold air, including making
contingency plans for any livestock or animals that reside outside.

While cold air is generally associated with clear conditions, there
is a shot for some ocean effect snow across the outer Cape Saturday,
likely driven by boundary layer delta temperatures approaching 30C.
The chance for these snow showers will be dependent on the position
of the high and the direction of the surface flow, but if NE flow
sets up across our waters, Cape Cod could see light accumulations of
fluffy snow.

Freezing spray is also likely to be an issue across the waters as
subfreezing temperatures and winds gusting 30-35kt will produce
hazardous conditions for mariners.

Sunday...

Temperatures rebound quickly for the second half of the weekend as
850mb temperatures rebound to -3 to -8C by Sunday evening. After a
chilly start to Sunday, temps may rebound as much as 20-30F across
portions of eastern MA.
-- End Changed Discussion --

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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Forecaster Confidence Levels:

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

18z TAF Update:

Rest of the Afternoon (thru 00z Mon): High confidence.

Mainly VFR ceilings thru the day; however lower-VFR/MVFR
ceilings possible late-day in NW MA and the terrain but away
from TAF sites. Still generally dry weather but an outside shot
at unrestricted -SHRA around ~20-00z especially east of ORH;
runways dry. S winds become SW around 10-13 kt this afternoon.
Occasional low-20s kt range for gusts across Cape and Islands.

Tonight: High confidence.

VFR ceilings, with lower-prob MVFR ceilings across northwest
MA. Mainly dry but a spot light shower possible thru 03z SE
MA/Cape Cod. SW winds around 10-13 kt (occasional 20 kt gusts
Cape Cod and Islands airports), veering to west after 05z and
diminish to 5-10 kt.

Monday: High confidence.

Mainly VFR, lowest ceilings around 035-040 west of ORH. Spotty
light rain after 20z but runways dry. W winds 4-8 kt, becoming
S late- day.

Monday Night: High confidence.

OVC lower VFR ceilings with MVFR ceilings for the south coast,
cape and islands. SW winds become WNW and increase to 10-15 kt,
with gusts around 20-25 kt.

KBOS Terminal...High confidence in TAF. Occasional 20 kt gusts
from the S but thinking more sustained winds. Outside shot at a
sprinkle, runways dry.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy.

Tuesday Night: VFR. Slight chance SN.

Wednesday through Wednesday Night: VFR.

Thursday through Thursday Night: VFR. Breezy.

Friday: VFR. Windy with gusts up to 35 kt.
-- End Changed Discussion --

&&

.MARINE...
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Forecaster Confidence Levels:

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

Small craft advisories remain in effect for the outer waters,
though for borderline SW gusts around 25 kt and seas in the 3-5
ft range.

Rest of Today: High confidence.

SW gusts around 15 to 25 kt, strongest offshore. Seas 3-5 ft.
Good visibility.

Tonight and Monday: High confidence.

SW gusts around 15-25 kt become W and ease to 15 kt tonight.
Winds become S around 10 kt Monday. Seas decrease to 2 to 4 ft
tonight and remain at that range through Monday afternoon.

Monday Night: Moderate to high confidence.

SW winds shift to NW and increase to around 20 kt. Chance that
gusts may reach into the SCA range for a brief period late-
overnight. Seas build to 3 to 5 ft.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of snow. Local visibility 1 nm or less.

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft.

Wednesday Night: Winds less than 25 kt.

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

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Seas up to 5 ft.

Friday: Low risk for gale force winds with gusts up to 40 kt.
Areas of rough seas. Chance of freezing spray.
-- End Changed Discussion --

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 5 AM EST Monday for ANZ250.
     Small Craft Advisory until 7 AM EST Monday for ANZ254>256.

&&

$$
SYNOPSIS...Loconto/KS
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...KS
AVIATION...Loconto/KS
MARINE...Loconto/KS