BOX issues Area Forecast Discussion (AFD) at Nov 20, 12:54 AM EST638
FXUS61 KBOX 200554
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1254 AM EST Wed Nov 20 2024
.SYNOPSIS...
High pressure will still be in control today, although will
gradually weaken with increasing cloud cover late in the day. A
slow-moving and well-developed area of low pressure looks to
spread cool overcast conditions along with welcomed rains to
Southern New England early tomorrow into Friday. Rain could mix
with wet snow above 1500 feet elevation by early Friday morning.
Drying out this weekend, although with considerable cloudiness,
blustery northwest winds and seasonably cool temperatures.
Mostly sunny and dry Monday but monitoring possible storminess
around Tuesday.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
* Diminishing wind tonight with lows upper 20s & 30s
A weak ridge of high pressure builds in from the west tonight. This
will allow winds to become calm/light and with mostly clear skies
should see a good night of radiational cooling. Overnight low temps
are expected to bottom out in the upper 20s to near 30 in the
normally coldest low-lying spots with mainly 30s across the urban
centers.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/...
Key Points...
* Plenty of sunshine Wed with highs 55-60 & light winds
* Increasing clouds Wed night with rain developing 4-8 AM Thu
Details...
Wednesday...
A mid level ridge axis will cross our region on Wed. This will
result in another day of plenty of sunshine...but much lighter winds
compared to the last two days. High should top off mainly in the 55
to 60 degree range.
Wednesday night...
Vigorous northern stream energy will be driving southeastward across
the Great Lakes Wed night. As this happens...surface low pressure
will intensify across the Great Lakes and also lead to secondary
development south of Long Island. This will induce a modest ESE
low level jet at 850 mb. While we expect much of Wed night to
feature dry weather...expect clouds to be on the increase. A
shield of widespread rain will then overspread the region from
southwest to northeast...roughly in the 4 to 8 am time frame.
Overnight low temps should mainly be in the upper 30s to the
lower 40s
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Highlights:
* Cloudy and seasonably cool with periods of rain showers Thurs
night into Fri night, with wet/slushy snow above 1500 ft
elevation.
* Gradual dry trend this weekend. Blustery with considerable
cloudiness Sat, with less cloud cover Sun. Temps seasonably
cool.
* Turning drier this weekend into early next week, but still remains
blustery and somewhat unsettled with seasonable temps.
* Drier and mostly sunny Mon, but possible storminess around
midweek.
Thursday Night through Friday Night:
Secondary area of low pressure near the eastern tip of Long Island
is forecast to retrograde NW into western New England Thurs night as
potent 500 mb low digs southward into the NYC/northern NJ vicinity.
00z EPS/GEFS/GEPS ensembles continue to show some spread on the
placement of the surface low via membership analysis, ranging from
central MA to as far west as the northern Catskills/Pocono Mtns, but
the majority of them are on the western end of solutions. Placement
of surface low north of the location of the upper level low is a
pattern which favors very slow/meandering movement as we move into
late Thurs night into early on Fri. As the low moves westward,
expect a decrease in steadier rains from daytime hrs Thurs to more
of an intermittent/showery character into Thurs night for most
areas. Cooling low-level profiles late Thurs night into early Fri AM
support rain mixing with wet snow above 1500 ft, mainly into the
Berkshires in western MA and some of the hills in far western
Hartford County. Even at these higher elevations, the exact position
of the surface low will affect any accums and rain will also mix in
with any accum being light and slushy; current thinking is that with
most ensemble members trending the surface low to our west, the
better chances for greater accumulation appears more restricted into
the hills in NY/western New England where precip rates may be more
noteworthy.
For Fri/Fri night...vertically-stacked cyclone will still be
overhead which will keep a generous amt of cloud cover around,
along with the threat for light rain showers but for most of the
day, any showers would be more pop-up/hit-or-miss. There
continues to be indication in the guidance of a second round of
steadier light rain later Fri aftn to Fri night, associated with
a shortwave trough rotating around the broader circulation.
However the location and placement of this rain varies
considerably. Best chances over eastern New England, but it may
lie just offshore or cover a wider portion of Southern New
England. Still think there is enough ensemble support to show an
increase in PoP back into the likely to categorical range for
later Fri aftn into Fri evening, on the higher end of that range
into eastern MA.
Rain amts...we still expect the bulk of the rain with this
slow-moving system to fall during the Thurs daytime timeframe.
But between Thurs night thru Fri, we could see an additional
half to three-quarters of an inch, on the higher end of that
range over western MA/CT with the steadier precip and
potentially into eastern MA.
Temperatures...gradual cold advection will allow for a cooldown in
temps toward more seasonable levels, but lots of clouds will keeps
lows from falling too far and keep highs from climbing much. For
Thurs night, lows in the mid 30s to low 40s, though will be around
freezing above 1500 ft elevation. Highs in the mid 40s to low 50s
Fri, with lows Fri night in the lower to mid 30s for most, with
upper 30s/near 40 for the eastern coast.
The Weekend:
Our upper level low pressure area will continue to gradually
progress NE into Maine Sat and then lurch into Atlantic Canada. This
will drive an increasingly blustery NW wind with potential for
decent mixing given cold pocket of air aloft.
Into Sat...there could be some wrap-around moisture around the low
pressure area near Maine which may still focus mostly cloudy
conditions and perhaps some higher-elevation rain/snow showers for
northern/northwest MA. Otherwise, looks to be a partly to mostly
cloudy day with NW gusts around 20-25 mph. Highs in the 40s to low
50s, with the wind making it feel around the mid 30s. Similar idea
for Sun as well, but there should be less cloud cover overall as
upper low continues to pull away with highs in the mid 40s to
low/mid 50s.
Monday and Tuesday:
Trending toward partly to mostly sunny conditions for Monday with a
brief warming trend back into the 50s with a southwest flow. However
will have to monitor another frontal system in the flatter WSW flow
coming out of the Midwest/OH Valley region. Lot of uncertainty
regarding this system in terms of timing and amplitude, with the
ECMWF being weaker and progressive, while the GFS/CMC are stronger,
with a timing either Mon night or during the day Tue. Didn't stray
far from NBM guidance in this period.
&&
.AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update:
Through 12z Wednesday: High confidence.
VFR, with a layer of SCT-BKN mid to high clouds western
airports. Light NW winds, calm at times.
Today: High confidence.
VFR continues for most of the day, though cloud cover will
steadily increase during the afternoon. Late in the day (after
22z?) we could see marine stratus from Nova Scotia advance
westward towards Cape Cod and could drop into the VFR/MVFR
borderline range here. Light N winds become NE/ENE by afternoon
with speeds 5-10 kt.
Tonight: High confidence in trends, but moderate on the timing.
Deterioration in all areas into at least the MVFR range before
rain arrives as marine stratus advances landward, soonest for
eastern MA but most airports should be sub-VFR by 05z. Leading
edge of widespread rains moves into western airports after 07z,
but could slip as late as 12z. NE winds around 5-10 kt, with
developing gusts around 20 kt near the coast.
Thursday: Moderate confidence.
MVFR-IFR ceilings with 3-6 SM steady light to moderate rains
breaking out in all areas during the early morning, before
gradually lifting northward through most of the aftn. As
steadier rain tapers off to more intermittent shower late in
the day, it is possible that ceilings/visbys could deteriorate
to solid IFR but this is uncertain. E winds increase to 10-15
kt with gusts 20-25 kt.
KBOS Terminal...High confidence in TAF. NE windshift as soon as
16z but more likely around 18-19z. Ocean stratus at MVFR levels
could set in as soon as 00z but more likely after 03z Thurs.
KBDL Terminal...High confidence in TAF.
Outlook /Thursday Night through Sunday/...
Thursday Night: Mainly MVFR, with areas IFR possible. Breezy.
RA.
Friday: Mainly MVFR, with local IFR possible. Breezy. RA
likely.
Friday Night: Mainly MVFR, with areas VFR possible. RA likely,
chance FZRA.
Saturday: Mainly VFR, with local MVFR possible. Windy with
areas of gusts up to 30 kt. Chance RA.
Saturday Night: Mainly VFR, with local MVFR possible. Windy
with local gusts up to 30 kt. Slight chance RA.
Sunday: Mainly VFR, with local MVFR possible. Breezy.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight and Wednesday...High Confidence.
A ridge of high pressure building in from the west will result in
conditions well below small craft advisory thresholds tonight and
Wed.
Wednesday night...High Confidence.
Intensifying low pressure over the Great Lakes will allow secondary
development south of Long Island. This will induce an easterly LLJ
late Wed night. Winds/seas will be below small craft advisory
thresholds for the majority of the night. Wind gusts should probably
approach small craft levels toward or around daybreak Thu. Given it
is very late in the 3rd and mainly 4th period event will let the
next shift handle the headlines.
Outlook /Thursday Night through Sunday/...
Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 10 ft. Rain.
Friday: Winds less than 25 kt. Areas of rough seas. Rain.
Friday Night: Winds less than 25 kt. Seas up to 5 ft. Rain.
Saturday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Chance of rain.
Saturday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 10 ft. Chance of rain.
Sunday: Strong winds with areas of gusts up to 30 kt. Rough
seas up to 10 ft.
&&
.FIRE WEATHER...
Wednesday...
High pressure building in from the west will result in much lighter
winds Wed compared to the prior two days. Minimum afternoon relative
humidity values are expected to be between 35 and 50 percent. After
collaboration with our area Fire Managers...we will be issuing a
special weather statement for Wed for the entire region once the
current RFW expires at 6 pm.
Thursday into Friday...
A much needed widespread 1" to 1.50" of rain is on tap for Thu into
Fri with even localized 2"+ amounts possible across the interior.
This should result in significant easing of the current Fire Weather
concerns.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Frank/Hrencecin
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...Loconto
AVIATION...Loconto
MARINE...Loconto
FIRE WEATHER...Frank
Source:
BOX issues Area Forecast Discussion (AFD) at Nov 20, 12:54 AM EST----------------
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