NWS Forecast Discussion
246
FXUS61 KBOX 210610
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
110 AM EST Thu Nov 21 2024
.SYNOPSIS...
A slow-moving low pressure area spreads welcomed steady light
to moderate rain today, before tapering to intermittent rain
showers tonight into early Friday. Rain could mix with slushy
wet snow above 1500 feet elevation tonight but no wintry impacts
are expected. Another round of steady light rain moves through
eastern New England Friday afternoon and evening. Low pressure
slowly progresses into the Maritimes for the weekend, with gusty
northwest winds and more clouds than sun are anticipated. Dry
weather then returns for Monday before an unsettled weather
pattern develops again for the middle of next week.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
730 PM update...
Dry, tranquil weather continues this evening and for much of the
overnight period. Clouds approaching from the west via WAA
aloft, along with low clouds approaching from the east given
onshore flow. However, much of the night will be dry. Leading
edge of the rain shield is across central PA into western NY.
Current radar and model trends still have the rain arriving into
western-central CT/MA between 09z-12z, then overspreading RI and
eastern MA between 12z-15z, possibly closer to noon for Cape Cod
and Nantucket. Some of the heavy rain will impact the AM commute
across western-central CT/MA, including Hartford and Springfield.
Not as chilly tonight as previous nights given increasing dew
pts and cloud cover. Lows 35-40, except 40-45 in the urban areas
and along the coast given onshore flow. Previous forecast
captures these trends, therefore no major changes with this
update.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
Thursday through Thursday night will be the main focus of the
forecast, especially for those with interest in seeing
diminished fire activity. The pattern makes a switch as the
upper low over the Great Lakes and its surface reflection sink
into the Mid- Atlantic. This spawns a secondary low pressure
center along the frontal boundary just off the east coast which
subsequently deepens as it lifts directly over southern New
England on Thursday and retrogrades backs toward eastern New
York Thursday night. A deep plume of moisture will accompany
this system with PWATs on the order of one inch. Strong dynamic
lift (35-45kt LLJ and 500 mb PVA) with the aforementioned
moisture will lead to a blossoming precipitation shield that
overspreads SNE from 2AM (west) to 10AM (east) and continues all
of Thursday and the first half of Thursday night before a dry
slot works its way north into the region. Thereafter showers
become more scattered in nature with the low continuing to be
just to our west.
Rainfall amounts continue to look solid for a meaningful rainfall,
with 1 to 1.75 inches possible; the heaviest amounts will be in the
high elevations of western MA where easterly upslope flow assists.
As for snow potential, there will be enough cold air aloft and
moving in on the back side of the system to bring some wet flakes to
the upper reaches of the Berkshires, mainly above 1500 ft. However,
not expecting efficient accumulation; a slushy inch or two are most
likely.
As for the winds on Thursday, it will be a blustery and cool day
with that LLJ overhead, easterly winds gusting 20 to 30 mph,
especially along the coasts; it will be a windy and rough day on the
our waters as well.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights:
* Cloudy, damp and overcast Fri night, with steady rains breaking
out in the coastal plain.
* Gusty NW winds this weekend, with more clouds on Sat along with
off-and-on showers. Seasonable temps but the winds will make it
feel cooler.
* Dry for Monday, but turning more unsettled into midweek.
Details:
Friday Night:
Cloudy, damp and unsettled conditions for Southern New England
continue into Fri night with vertically-stacked circulation
continuing to meander around western New England/southern NY
vicinity. However there still looks to be a round of steadier light
rains which develop/rotate NNW from the southern waters into eastern
MA, the Cape and the Islands. Looking at GEFS/EPS/GEPS ensemble
members, there is a significant enough majority of members which
keep this secondary burst of steadier rains into the MA/RI coastal
plain with lighter intermittent precip over western MA/CT. However
QPF amts are still pretty variable; while QPF amts are more commonly
in the quarter to half inch range in the coastal plain thru Fri
night, there are a minority of members up to 3/4ths an inch. By
early Sat AM, this band of steadier rains should shift NNE into
coastal ME/NH as the broader upper level low begins to pull
offshore.
The Weekend:
Ensembles continue to trend toward a slower NE departure of the
upper-level low and its cold pocket of air aloft for the weekend.
Thus a trend toward cloudier conditions for Sat with off-and-on
light showers, with better chances in eastern and northern MA, Cape
and Islands. Less cloud cover in general for Sunday, with more
in/around the terrain but with drier conditions. Highs on Sat in the
40s to around 50, and with a pretty strong NWly gradient flow and
cloud cover, lows may only fall into the upper 30s to low 40s. With
less cloud cover, highs Sun in the 40s to lower 50s with lows in the
30s Sun night.
The cooler temperatures aloft and a robust NW gradient flow will
also contribute to rather blustery to gusty NW winds through the
weekend. Model soundings also continue to show mixing up to about
900 mb on Sat, and slightly higher around 850 mb for Sun with a
little less cloud cover and slightly warmer temps. For Sat, NW gusts
could reach into the 25 to 30 mph range during the daytime hrs.
Strongest 925 mb jet of 35-40 kt moves thru Sat night into early on
Sun, and we should still realize gusts around 20-25 mph into the
evening for most areas, but could punch up to around 35-45 mph over
the Berkshires, hills in Worcester County as well as the Cape and
Islands. Still see gusts in the 25 to 35 mph range for Sunday thru
the early afternoon, then beginning to subside late in the day as
gradient starts to relax and low level jet core shifts offshore.
Potential for gale headlines for the waters, although over land,
confidence in gusts reaching Advisory levels is lower but could be
possible if we mix deeper. Will reassess gusts as we get into the
mesoscale model forecast horizon.
Monday:
Still looking at pretty tranquil weather conditions for Mon with
weak shortwave ridging aloft and modest SW winds allowing for highs
in the low to mid 50s.
Monday Night through Wednesday Night:
A more active weather pattern is indicated by most of the ensembles
into the early to middle part of next week, as slow-evolving trough
energy circulating over the West Coast/Pac NW begins to eject
eastward off the Rockies. At least one frontal system moves in
during this period, around the Mon night/Tue timefame, although
there are still significant differences in strength with this
potential system. Forecast confidence is still on the low side in
this period and stayed fairly close to NBM forecasts for this period
until those differences shake out.
&&
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update:
Through 12z Thursday: High confidence in trends, moderate on
timing.
MVFR stratus initially (IFR at ORH) with dry weather for at
least another couple hrs. Steady light to moderate RA with vsbys
3-6 SM now over the lower Hudson Valley then breaks out into
BAF/BDL around 08-10z, and into central MA/RI by ~10-12z. Better
chance for steadier rains eastern airports just after 12z.
Ceilings may trend closer to MVFR/borderline IFR range as steady
rain breaks out. Light E winds to start but will increase to
around 7-10 kt thru 12z Thurs.
Today: Moderate confidence.
3-5 SM RA spreads across all airports early this AM, which
continues into early tonight. Rain will become increasingly
wind-driven as E winds increase to around 10-15 kt with
gusts 20-25 kt near the E MA coast.
MVFR/IFR ceilings continue, though ceilings likely to dance
between 800-1500 ft most of the day. Took a pessimistic
approach with the TAFs indicating IFR, however there could be
MVFR intervals in between but difficult to pinpoint a timing.
Tonight: Moderate confidence.
Widespread 3-6 SM steady RA early tonight trends to more of an
intermittent -SHRA or even -DZ between 00-06z, earliest south
and later north. Steadier light rain likely to continue at
BAF/BDL. Improvement in ceilings toward OVC MVFR interior, and
become BKN/OVC VFR over eastern/southeast New England. Winds
start E around 10-15 kt with gusts 20-25 kt, though will become
SE/S around 10-14 kt with lesser gusts to around 20 kt.
Friday: Moderate confidence.
MVFR ceilings with periods of -RA interior CT/MA, BKN/OVC VFR
ceilings with initially dry wx eastern airports. Later in the
afternoon a band of rain moves northward from the ocean and
spreads across eastern MA/RI, exact timing uncertain but likely
not sooner than 18z. SE to S winds around 7-14 kt with gusts up
to 20 kt.
KBOS Terminal...Moderate confidence in TAF. MVFR cigs initially,
trending IFR/MVFR with 3-6 SM RA developing around ~12-13z.
Cigs could flip between IFR-MVFR levels frequently today.
Wind-driven rain on ENE/E winds around 15 kt today with gusts
20-25 kt. RA tapers off around 03z to a intermittent
light -SHRA, with winds becoming SE around 10-13 kt.
KBDL Terminal...Moderate confidence in TAF. MVFR cigs initially,
trending IFR-MVFR w/ 3-6 SM RA developing around ~08-10z. Steady
light to moderate RA continues thru about 02z before lightening
up. E winds around 10 kt today, becoming SE tonight.
Outlook /Friday Night through Monday/...
Friday Night: Mainly MVFR, with local IFR possible. RA likely.
Saturday: Mainly VFR, with local IFR possible. Windy with local
gusts up to 30 kt. Chance RA.
Saturday Night: Mainly VFR, with local MVFR possible. Windy
with gusts up to 35 kt. Slight chance RA.
Sunday: VFR. Windy with gusts up to 35 kt.
Sunday Night: VFR. Breezy.
Monday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
This evening through Thursday night...
Calm/tranquil conditions this evening with weak high pressure
supporting light winds over the coastal waters. 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 /Friday Night through Monday/...
Friday Night: Winds less than 25 kt. Seas up to 5 ft. Rain.
Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Rain likely.
Saturday Night: Moderate risk for gale force winds with gusts
up to 35 kt. Rough seas up to 11 ft. Chance of rain.
Sunday: Strong winds with gusts up to 35 kt. Rough seas up to
10 ft.
Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.
Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 10 AM this morning to 1 PM EST
Friday for ANZ231>234-251.
Small Craft Advisory from 5 AM early this morning to 7 PM EST
Friday for ANZ235-237.
Small Craft Advisory from 10 AM this morning to 7 AM EST
Saturday for ANZ250-254-255.
Small Craft Advisory from 5 AM early this morning to 7 AM EST
Saturday for ANZ256.
&&
$$
SYNOPSIS...Loconto/RM
NEAR TERM...BW/Nocera
SHORT TERM...BW
LONG TERM...Loconto
AVIATION...Loconto/RM
MARINE...Loconto/RM
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