BOX issues Area Forecast Discussion (AFD) at Dec 3, 3:50 PM EST973
FXUS61 KBOX 032050
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
350 PM EST Tue Dec 3 2024
.SYNOPSIS...
Dry and cold weather continues tonight and Wednesday...but a few
brief snow showers may impact parts of interior southern New England
into early this evening. An Alberta Clipper will bring accumulating
snow to the high terrain northwest of I-495 Wednesday night into
Thursday morning with mainly rain on the I-95 corridor. A strong
cold front may bring a few snow squalls Thursday and also result in
strong winds developing. Blustery and colder Thursday night and
Friday with temperatures well below normal. It remains cold Saturday
but with less wind, then a moderating trend begins Sunday with
above normal temperatures returning early next week. Mainly dry
weather expected through the weekend, then rain chances will
increase early next week as a frontal system approaches from the west.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
350 PM Update...
* A few brief snow showers possible into early eve in the interior
* Otherwise...dry and cold tonight with lows teens to the lower 20s
* Sunshine gives way to clouds Wed with highs upper 30s/near 40
Tonight...
A shortwave and remnant Lake Effect moisture may allow for a few
snow showers/flurries to impact our interior zones into early this
evening...especially across southwest MA/northern CT and perhaps
even parts of RI. Otherwise...another dry and cold night of weather
is on tap for the region. After a round of scattered to broken
clouds into part of the evening...skies should trend to mostly clear
overnight. This combined with winds becoming calm/light from the NW
should allow for a good night of radiational cooling. Overnight low
temps should bottom out in the teens to the lower 20s in most
locations with middle 20s in the Urban Heat Island of Boston.
Wednesday...
An Alberta Clipper will be dropping southeast across Ontario on Wed.
Sunshine during the first part of the day...will give way to
increasing clouds during the latter half of the day. Temps will
again be chilly/below normal for this time of year. Highs will
mainly be in the upper 30s/near 40 with readings a bit cooler in the
higher terrain.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/...
Key Points...
* Accumulating Snow higher terrain northwest of 495 Wed night/Thu AM
* Ptype mainly rain towards & especially southeast of I-95
* Greatest uncertainty with Ptype is across interior lower elevations
* A strong cold front may bring a few snow squalls later Thu
* Turning quite windy Thu afternoon & night with NW gusts 35-50 mph
Details...
Wednesday night into Thursday morning...
The Alberta Clipper will be moving across Quebec and northern New
England Wed night into Thu morning. This will induce a strong
southwest LLJ at 850 mb of 45 to 60 knots. There is also a good
signal for a period of modest mid level frontogenesis ahead of this
clipper system. This should allow widespread precipitation to
overspread the region from west to east between 8 pm and midnight.
In addition...this strong southwest LLJ should mix quite well near
the south coast given relatively chilly boundary layer temps.
Thinking southwest winds will gust to between 30 and 40 knots later
Wed night towards the Cape and Islands. May even be marginal Wind
Advisory criteria for parts of this region.
Ptype/Snow Accumulations...
The main question is Ptype across the region Wed night into Thu
morning. Given that this storm is passing to our north and there is
no cold high pressure system in place to our north...southwest flow
will allow for boundary layer to warm nicely along the Boston to
Providence corridor. Ptype in this region should mainly be rain.
Some of the guidance indicates rain could end as a bit of snow...but
do not think it will amount to much if anything. Thermal profiles &
soundings indicate that the boundary layer will remain cold enough
to support mainly snow in the high terrain to the northwest of I-
495. We are thinking 2-5" of snow across much of the interior high
terrain across western and central MA with perhaps isolated 6"
amounts in the highest terrain. We have gone ahead and issued a
Winter Weather Advisory for these locations. The main concern will
revolve around the Thu morning commute where roads may be snow
covered and slippery. Confidence on Ptype is more uncertain in the
lower elevations particularly in the Springfield to Hartford areas.
We could struggle to get much accumulation if boundary layer trends
warmer...but if rates are able to overcome that warmer boundary
layer may get a quick few inches.
So in a nutshell...we are confident in accumulating snowfall across
the interior high terrain and mainly rain along the I-95
corridor...although a bit of snow is possible before the
precipitation ends Thu morning. The greatest uncertainty in
Ptype/Snow amounts is across the lower elevations of the
interior...especially in the Springfield to Hartford metro areas.
Later Thursday morning and afternoon...
While the steady rain and snow will have exit most of the region by
mid-late Thu morning...a strong cold front will follow. This will be
associated with a strong shortwave/steep low level lapse rates in
the 1000-700 mb layer along with a fair amount of low level moisture
left over. In fact...the guidance is showing a few hundred J/KG of
MUCape. Therefore...a few snow squalls will be possible on Thu with
brief localized very poor visibility and strong wind gusts. The
primary concern for travel issues will again be across the interior
where temps will be colder and snow may quickly coat roads in any
localized snow squalls. We will have to monitor this closely over
the next 24 hours. Towards the I-95 corridor boundary layer may be
warm enough for a mix of scattered rain/snow showers.
Otherwise...a strong westerly low level jet coupled with cold
advection will result in the development of strong winds. Wind gusts
on the order of 35 to 50 mph are expected to develop later Thu into
Thu evening. Wind Advisories may be needed for portions of the
region.
High temps in the upper 30s to the middle 40s will fall later in the
day and evening as strong cold advection takes over.
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Key messages:
* Blustery and colder Thursday night and Friday
* Still cold Saturday but with less wind
* Moderating temps Sunday warming to above normal early next
week
* Mainly dry through the weekend, then rain chances return early
next week
Details...
Thursday night through Sunday...
Arctic front will be offshore by Thu evening with gusty W winds
bringing in a rather chilly airmass Thu night and Fri as 850 mb
temps bottom out around -13 to -15C Fri. Temps well below normal Fri
with highs upper 20s and lower 30s for much of SNE. The cold will be
accompanied by gusty W winds 25-40 mph which will drive wind chills
down into the teens and low 20s on Fri. Not quite as cold Sat but
still below normal (highs in 30s) with less wind, then temps begin
to moderate Sunday as SW flow develops. A few snow showers may
linger into Thu evening over the Berkshires, otherwise mainly dry
conditions expected through the weekend as high pres gradually
builds east to the mid Atlc coast.
Monday and Tuesday...
Forecast confidence decreases early next week as a pattern change
develops with a shift to SW flow aloft as upper trough digs into the
Rockies. A series of fast moving shortwaves lifting NE toward New
Eng will bring a risk of showers at times early next week but timing
is uncertain. We have higher confidence in a warming trend with
above normal temps likely returning as notable warming occurs in the
low levels. Temps will likely get back into the 50s for at least a
portion of SNE, especially on Tue. This is supported by GEFS/EPS/CMC
ensembles which all indicate high probs of temps above 50F by Tue,
especially south of the MA Pike.
&&
.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update...
This afternoon and tonight...High Confidence.
VFR outside a few brief flurries/snow showers may impact
portions of the interior with the best chance across southwest
MA/northern CT. NW winds 5-10 knots diminishing tonight in the
typical low- lying spots.
Wednesday...High Confidence.
VFR. Winds becoming SSW at 5 to 15 knots.
Wednesday night and Thursday...Moderate Confidence.
Precipitation will overspread the region from west to east
mainly during the latter half of Wed evening. This will result
in widespread low end MVFR-IFR conditions developing with LIFR
conditions possible across the interior as the night wears along.
As the widespread precipitation departs Thu morning...conditions
should improve to mainly MVFR and even VFR in some spots Thu
afternoon.
Ptype will mainly be snow northwest of I-495 with generally
rain southeast of that region Wed night into Thu morning. Ptype
could mix with or change to snow towards the I-95 corridor for
a brief time before the bulk of the precipitation ends Thu
morning. Snow accumulations of 3-6" are expected across the
interior high terrain with 1-3" in the lower elevations of the
interior. Little if any snow accumulations on the I-95 corridor
with precipitation mainly in the form of rain. The steady
precipitation will come to an end Thu morning...but a strong
cold front will bring a few rain/snow showers and the potential
for a couple of heavier snow squalls too.
SSW winds at 5-15 knots are expected Wed night...but will be
stronger on the order of 15 to 30 knots with perhaps some gusts
up to 40 knots later in the night towards the Cape and Islands
with a strong LLJ. Winds shift to the west on Thu with gusts of
30-40 knots developing behind the strong cold front.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Thursday Night through Sunday/...
Thursday Night: VFR. Strong winds with areas of gusts up to
45 kt.
Friday: VFR. Windy with gusts up to 35 kt.
Friday Night through Saturday Night: VFR. Breezy.
Sunday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
* Gale Warnings Wed night and Thu
Tonight and Wednesday...High Confidence.
Northwest winds on the order of 10 to 15 knots tonight will shift to
the southwest on Wednesday. This a result of an Alberta Clipper
dropping southeast across Ontario. Winds/Seas will generally remain
below small craft advisory thresholds...but may see some southwest
wind gusts of 20-25 knots across the southern waters by late
Wednesday and perhaps some marginal 4-5 foot seas.
Wednesday night and Thursday...High Confidence.
A strong southwest LLJ ahead of an Alberta Clipper will allow
southwest wind gusts of 30 to 40 knots to develop Wed night and then
shift to the W behind a strong cold front Thu. In fact...we may see
some gusts up to 45 knots on Thu behind a strong cold front. Gale
Warnings have been posted for all our waters.
Outlook /Thursday Night through Sunday/...
Thursday Night: gale force winds with gusts up to 45 kt. Rough
seas up to 14 ft. Slight chance of rain showers.
Friday: Strong winds with gusts up to 35 kt. Rough seas up to
11 ft.
Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas.
Saturday: Winds less than 25 kt. Seas up to 5 ft.
Saturday Night through Sunday: Winds less than 25 kt. Areas of
seas approaching 5 ft. Slight chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Winter Weather Advisory from 8 PM Wednesday to 10 AM EST
Thursday for MAZ002>004-008>010-012-026.
RI...None.
MARINE...Gale Warning from 7 AM Thursday to 7 AM EST Friday for ANZ230.
Gale Warning from 7 PM Wednesday to 7 AM EST Friday for
ANZ231>237-250-251-254>256.
&&
$$
SYNOPSIS...Frank/KJC
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...KJC
AVIATION...Frank/KJC
MARINE...Frank/KJC
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 3, 3:50 PM EST----------------
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