BOX issues Area Forecast Discussion (AFD) at Nov 20, 12:34 PM EST694
FXUS61 KBOX 201734
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1234 PM 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 PM THIS EVENING/...
Today
The forecast remains on track this update. A mid-level ridge
axis builds over southern New England today. This will support
another afternoon with seasonable temperatures and more sun than
clouds. Winds will be much lighter today initially out of the
north/northwest but eventually veering to east/northeast during
the afternoon. With east/northeast winds supporting more onshore
flow, the coastal areas can expect increasing cloudiness this
afternoon and evening. Highs temps will be similar to yesterday
in the mid to upper 50s.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Tonight and Tomorrow
After a rather long dry streak that has resulted in drought
conditions across southern New England over the last month or
so, we will finally receive some relief tonight into Thursday. A
low-pressure circulation will develop off The Mid-Atlantic
coast this evening and overnight. This will be the product of a
parent low-pressure system that will be occluding over The
Great Lakes Region. As this secondary low-deepens and
progresses east/northeast just off the south coast of southern
New England, the forecast area will begin to see widespread
rainfall sweep over the region. Latest forecast guidance
supports rain beginning across the western areas a couple of
hours after midnight and eventually reaching the east coast of
MA during the morning commute. Winds increase to 10 to 15 mph
out of the east with some gusts to 20 mph. Overnight lows fairly
seasonable in the upper 30s to low 40s.
Generally a washout for Thursday as soaking rain persists for most
of the day in southern New England. Atmospheric forcing looks to be
moderate based on model derived mid-level FGEN. Furthermore there
will be plenty of moisture with PWATs rising above an inch. As a
result most of southern New England can expect a much needed 1+
inches of rain between tonight and tomorrow. Deterministic QPF
forecast is about an inch for most locations through tomorrow
evening, but if we consult ensemble guidance we find that the
potential exists for substantially more than that with
probabilities of 1.5 inches or more ranging from 30 to 60
percent across southern New England. Clouds and rain will limit
high temperatures to the upper 40s/low 50s across the region.
Precipitation persists into tomorrow night as the low-pressure
center eventually retrogrades west into New York on Friday (see
long term AFD for more details.)
&&
.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 /18Z WEDNESDAY 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: High confidence.
VFR continues for most terminals, with a patch of MVFR marine
stratocu advancing WSW toward Cape Cod. Cloud cover steadily
increases during the afternoon from the west for the remaining
terminals. Late in the day we could see marine stratus from Nova
Scotia. Light N winds become NE/ENE by afternoon with speeds
5-10 kt.
Tonight: High confidence in trends, moderate on the timing.
Conditions deteriorate at all terminals with the arrival of
stratus and RA, soonest for eastern MA but most airports should
be sub-VFR by 05z. Leading edge of widespread rains moves into
western airports after 11z. NE winds around 5-10 kt, with
developing gusts around 20 kt near the coast.
Thursday: Moderate confidence.
MVFR-IFR cigs with 3-6 SM steady -RA/RA during the early
morning, gradually lifting northward through 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 remains uncertain. E winds increase to 10-15
kt with gusts 20-25 kt.
Thursday night: Moderate confidence.
Rain becomes more scattered in nature through the overnight
hours with IFR conditions becoming MVFR then VFR for eastern MA
terminals between 06 and 12Z.
KBOS Terminal...High confidence in TAF. 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: MVFR/IFR conditions possible. Windy with local
gusts up to 30 kt. 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.
Today through Thursday
Calm/tranquil conditions today with weak high pressure supporting
light winds over the coastal waters today. Conditions begin to
deteriorate overnight as an area of low-pressure moves over the
south coastal waters. Winds strengthen out of the east to speeds of
15 to 25 knots with gusts up to 30 knots by tomorrow. Moderate
easterly winds continue through the day Thursday with seas building
to 6 to 8 feet. A few gale force gusts up to 35 knots will be
possible, especially over the southern marine zones through Thursday
afternoon. However, confidence in a prolonged period of gales is not
high enough to warrant gale headlines. Nonetheless, solid SCY
conditions will be present over the coastal waters likely through
much of the day Friday and beyond.
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...Small Craft Advisory from 10 AM Thursday to 7 AM EST Friday
for ANZ231>234-250-251-254-255.
Small Craft Advisory from 5 AM Thursday to 7 AM EST Friday for
ANZ235-237-256.
&&
$$
SYNOPSIS...Loconto/RM
NEAR TERM...RM
SHORT TERM...RM
LONG TERM...Loconto
AVIATION...BW/RM
MARINE...Loconto/RM
FIRE WEATHER...Frank
Source:
BOX issues Area Forecast Discussion (AFD) at Nov 20, 12:34 PM EST----------------
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