Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 281330

Area Forecast Discussion
National Weather Service Boston/Norton MA
930 AM EDT Thu Sep 28 2023

Dry and pleasant weather continueS today with increasing clouds
this afternoon and evening. Uncertainty with Friday, through
best chance for rain would be along the south coast of New
England. Rain continues on Saturday and perhaps into early
Sunday for portions of the region. This is highly dependent on
how far north a low tracks. High pressure builds in for much of
the upcoming week. Above normal temperatures anticipated.


930 AM Update...

Vsbys starting to improve across interior MA and CT so we have
dropped the dense fog advisory. Stratus and fog still persists but
should burn off between 10 am-noon followed by increasing  sunshine.
However, low level moisture will be increasing from the south and
west leading to redevelopment of stratus later in the afternoon,
mainly along the RI coast to portions of CT.
overall, a pleasant afternoon with temps recovering into the
mid/upper 60s with easterly winds 5-15 mph.

Previous discussion...


* A cool morning with areas of fog does gives way to a pleasant
  afternoon, though with increasing clouds and seasonable

Starting the day with temperatures in the upper-30s to mid-40s and
areas of radiation fog, a typical start to a fall day for southern
New England. Do not expect the areal extent of the fog to reach
advisory criteria, but locally dense fog in prone areas is not out
of the question. There visibilities may be reduced to less than 1/2
mile. Given the clear sky cover do not expect the fog to stick
around for too long, likely eroding between 7-9 AM.

A 1028mb high to the north will provide another dry, mostly sunny
afternoon, along with seasonable temperatures. With Canadian high
pressure systems, the temperatures aloft are usually on the cooler
side, forecast 925mb temperatures are between +10C and +12C. Based
off BUFKIT soundings, mixing of the boundary layer extends to 950mb
and this yields maximum temperatures between 65 and 70 degrees.
Though it will be cooler at the coast given NE winds around 10 mph.



* Mainly a dry night, but there remains a fair amount of uncertainty
  with timing and extent of rainfall on Friday.

Thursday Night: Surface high pressure moves east, over the Canadian
Maritime as a mid-level low and shortwave approaches from the west.
This will increase cloud cover overnight. As mentioned by the
previous forecaster, there remains great uncertainty with this part
of the forecast because of the disagreement among many to the global
models. That said, we are now able to utilize the CAMs, as we are 48
hour window. Among the CAMs, there is good agreement from 00z to 12z
for widespread rain across the Hudson Valley and east into western
Connecticut and Massachusetts. Did trend POPs higher for the western
CWA as result. Due to increase cloud cover, do not expect
radiational cooling, resulting in overnight lows about 5-8 degrees
warmer than last night, 45-50 degrees, though eastern/coastal
MAssachusetts are 50-54 degrees.

Friday: There remains poor agreement among guidance, which includes
the CAMs. After fairly decent agreement for Thursday night, the
guidance seems to become split for the daylight hours of Friday. The
global ensembles are far from being in agreement, the 00z GEFS has
between a 30 and 50 percent chance of 0.5" inch between 00z Friday
and 00z Saturday. While the ECMWF ENS delivers a 60-70+ percent. And
for what it is worth, the ECMWF ENS does have low probs for 2.0 or
greater of rainfall mainly across Connecticut and Rhode Island.

Given the setup, a mid-level low to our west and developing surface
low to our south, opt to keep the highest POPs across the south
coast of New England. As this is a low confidence forecast, would
not be surprised to see adjustments after reviewing the 12z

Temperature wise, cloud cover keeps us cooler especially western
locations, between 60-64 degrees. Where we don`t see rain, mainly
eastern Massachusetts the temperature could reach 64-68 degrees.



* Rain Fri night through much of Sat. Still uncertain on precip
  amounts and the north/northwest extent of the precip shield.

* Drier Sun through a good portion of next week. Temperatures
  trending above normal.

Friday Night through Saturday Night...

A trough/cutoff over the eastern Great Lakes/Mid Atlantic Fri night
will rotate over/just south of southern New England by early Sat.
The trough/cutoff lifts offshore by late Sat/early Sun. A broad low
off the Mid Atlantic coast Fri night will lift E/ENE through Sat/Sat
Night. Still uncertain how close this low along with an inverted
trough tracks to our region.

Have trended the forecast in a wetter direction in the latest
update. Unfortunately there is still a fair amount of uncertainty
with how far northward the low/inverted trough track. Deterministic
along with ensemble guidance has gradually been trending in a wetter
direction the past couple of days. The ECMWF/EPS guidance still the
wettest of the bunch with quite a wet Fri Night/Sat for southern New
England. The GFS/GEFS still the drier of the solutions, but has
gradually been getting wetter from run to run. The GEM/GEPS is a
pretty good compromise between the two. Have leaned more toward a
consensus approach given the spread in solutions. Did bump PoPs up
across the south coast to high chance/likely in the latest update
with slight chance to chance further to the N/NW. Should see these
chances gradually come down later on Sat as the low lifts further
offshore and high pressure begins nudging in.

Will need to hone in on where the closed upper low tracks. The
further north closed off low tracks the better shot for heavier
precipitation as it will really advect the tropical PWATS into our
region. At the moment the ECMWF/EPS is along the south coast with
the 700 hPa closed off low, whereas the GFS/GEFS and GEM/GEPS are
further south. The further southerly solution keeps 1-1.5 inch PWATs
generally south of the MA Turnpike, whereas the northerly has PWATs
approaching 2 inches across SE MA with much of the region in 1-1.5
inch PWATs. Hopefully guidance comes into further agreement today,
but if things continue to trend in the ECMWF direction we may need a
Flood Watch for parts of the region. Best shot for 24 hr precip AOA
1 inch is along the immediate south coast, but perhaps as far north
of the MA Turnpike. Probabilities are 40-80 percent with the
GEPS/EPS guidance and 10-40 percent with the GEFS.

Did bump down our temps on Sat across southern New England. The NBM
appears much too warm given the prolonged NE/ENE flow through the
day. Blended toward the latest NAM guidance, but may need to lower
temps further depending on the low track. Temps will be near to
slightly cooler than seasonable.

Sunday through Thursday...

Ridge axis in place over the Lower Mississippi River Valley to the
Great Lakes Region on Sun with a cutoff low south of Nova Scotia.
The cutoff continues to move offshore later on Sun while the ridge
remains in place. The ridge builds into the Mid Atlantic/eastern
Great Lakes on Mon. The ridge flattens out a bit late Mon through
Tue before it re-establishes itself over the eastern Great Lakes for
mid/late in the week. High pressure builds over the Mid
Atlantic/eastern Great Lakes for much of this period.

Dry and quiet weather expected through most of this timeframe. Not
completely out of the question there is still some light precip
lingering across parts of the south coast early on Sun, but drier
air will be pushing in as high pressure builds in. Did not make any
major adjustments to the extended from the NBM given the uncertainty
in the Fri Night to Sat Night timeframe. Temperatures will be on the
rise as winds aloft shift to a W/NWly direction early next week. The
latest NAEFS SATA table still indicating temps 1.5 to 2.5 STD above
norm for the Northeast through much of this period. Guidance has
backed off on the 80+ warmth for Mon, but still have some lower
probs in the Tue-Thu timeframe per the GEFS/EPS guidance. For now
have temps solidly in the 70s through much of this timeframe with
lows in the 50s.


Forecast Confidence Levels:

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

Today...High confidence.

Any VLIFR to MVFR stratus/fog burns off by 13-15Z. May be
locally dense especially across the typical fog prone locations.
After 15Z all areas will be VFR with NE winds shifting to the
ENE at 5-10 kts.

Tonight...Moderate confidence.

VFR conditions for most, but could see MVFR to perhaps IFR
stratus/fog spreading in. Have added rain to the TAF for
BAF/BDL. Light ENE to E winds.

Friday...Moderate confidence.

Generally VFR with RA and E/NE winds at 10 kts. CIGS may lower
to MVFR and perhaps IFR if system tracks closer to the region.
Rainfall also could be heavy at times, especially if the system
tracks closer.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night through Saturday: Mainly VFR, with local MVFR
possible. Breezy. Chance RA.

Saturday Night through Sunday Night: VFR. Breezy.

Monday: VFR.


Forecaster Confidence Levels:

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

Tonight through Thursday night...High Confidence.

ENE flow will continue through Thursday night but gradient has
weakened across the northern waters with high pressure across
eastern Canada moving southeastward. headlines
will be needed for our northern waters as well as sounds/Bays.
However...across the southern waters some 5 foot seas will hold
along with 20+ knot wind gusts. Therefore...have extended small
craft headlines for our southern most waters right through
Thursday night.

Outlook /Friday Night through Monday/...

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain.

Friday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain.

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Slight chance of rain.

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

Sunday Night through Monday: Winds less than 25 kt. Seas up to
5 ft.


MARINE...Small Craft Advisory until 4 PM EDT this afternoon for ANZ254.
     Small Craft Advisory until 8 PM EDT Saturday for ANZ255-256.


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