Area Forecast Discussion
National Weather Service Boston/Norton MA
143 AM EST Sat Dec 2 2023

.SYNOPSIS...
Spotty light showers, drizzle and areas of fog early Saturday
morning, gives way to mainly dry weather during the daylight 
hours, along with mild temperatures. Mainly dry weather lingers
into Saturday evening, but then rain redevelops overnight and 
gives way to a rainy, cool Sunday, as low pressure develops 
south of New England. A drying trend follows Monday as the low 
departs. While temperatures will be above normal to open the new
workweek, temperatures then steadily fall to near or slightly 
below normal through the middle portion of the week. Our next 
chance for precipitation after Sunday comes with a progressive 
area of low pressure on Friday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...

1:30 AM Update:

Moist SSW flow (dew pts in the 40s) in the warm sector across
SNE, this moisture is now becoming trapped beneath dry slot 
aloft overspreading the region and is resulting in widespread 
fog across the area. This trend will continue into the early 
morning hours. Given dew pts are well above normal for early 
Dec, some of the fog could become locally dense. Mild overnight
with lows only in the 40s, except upper 30s across western MA. 

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...

Highlights: 

* Plenty of clouds and areas of drizzle Saturday, but temperatures 
  are once again mild, returning to the lower and middle-50s. 

* Areas of fog during the first-half of Saturday night and followed 
  by the next chance of rain second-half of the night into Sunday. 

Weak surface low pressure moves from the Ohio River Valley into New 
England on Saturday. While there is not much moisture with this 
incoming system, the forecast sounding have a pretty strong 
inversion just above the surface. Out thoughts are trending towards 
an overcast day with areas of morning fog giving way to areas of 
drizzle. Continued southwest flow promotes mild temperatures, highs 
tomorrow afternoon return to the low and middle-50s. Southwest wind 
generally 5-10 mph. 

A wind shift to the northeast occurs late Saturday afternoon/early 
evening, reinforcing our stratus deck of clouds into the overnight 
hours. Lows overnight area mild, middle-30s to middle-40s. Dewpoints 
are elevated as well for early December, dewpoints in the upper-30s 
and middle-40s. Surface winds are light, less than 5 mph, this may 
lead to ground fog to develop early in the night. An approaching low 
pressure system to our west ushers in the next round of rain to the 
area early Sunday morning. Details regarding that can be found in 
the long term section of our AFD.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

Highlights: 

* Soggy Sun into early Mon with mainly plain rain, although a brief 
  mixover/end as wet snow in the higher elevations in northern MA is 
  possible. Above normal temps are favored Sun and Mon.

* Cooler and mainly dry Tue thru Thurs, although there may be 
  considerable cloudiness around. 

* Though a Clipper system projects to pass to our south on Wed, a 
  better chance at precip associated with another Clipper system 
  arrives around Fri, offering our next chance for precip after 
  Sun/Mon.

Details:

Sunday and Monday: 

Complex area of low pressure is expected to move ENE from the 
coastal mid-Atlc early on Sun into coastal Southern New England 
through Sun. Steady rain is likely to be ongoing along the immediate 
southern coast, however rain shield will be steadily advancing 
northward from the south coast through the morning to early 
afternoon hrs. Thus advertised increasing PoP to categorical levels 
for steady rains during the late morning to midafternoon hrs. 
Temperatures should be warm enough for entirely rain even at 
elevation at least during the daytime hrs. For later in the day into 
the evening, it does look like a dryslot comes in across areas near 
and south of the Mass Pike which would bring decreased rain chances 
for these locations, with better chance for rain Sunday evening into 
early Mon lying north of the Mass Pike. Will note that further north 
into interior northern New England, colder air associated with a 
1020+ mb high pressure is expected to wedge SSW through the 
mountains of ME/NH during the day on Sun. Earlier ECMWF solutions 
which were on the slower end of the guidance envelope offered some 
potential for rain to mix with snow in the higher elevations Sunday 
evening due to this colder air. However today's ECWMF now seems to 
mesh more closely with the GFS and the Canadian in restricting 
colder air supportive of snow/rain mix or pure snow into NH/VT. This 
colder air will eventually progress S/SE on Mon, but by then precip 
looks to be either in the process of winding down or having ended 
entirely. All in all, looking to be a soggy Sunday into overnight to 
early Mon AM with an outside chance for rain to mix with snow in the 
highest of elevations Sunday evening/night; precip then ends on Mon 
while colder air filters in on N/NW winds. 

With lots of cloud cover and potential for some dynamic cooling as 
low pressure pulls away on Mon, ended up deviating a bit from NBM 
highs/lows toward a narrower diurnal range for both Sun and Mon. 
Expect highs in the 40s to low 50s on Sun, with lows in the mid 30s 
to the lower to mid 40s (low 30s in the Berks and northern Worcester 
hills). Highs on Mon should be a little cooler than Sun but still in 
the 40s. Meanwhile may still be contending with leftover cloudiness 
but should be on the decrease for Mon night, thus offered lows in 
the upper 20s to the mid 30s.

Tuesday through Thursday: 

Weak high pressure along with cool cyclonic flow aloft governs this 
period. It is overall a dry pattern, although there may be a low 
chance for showers along the immediate southern/southeast coastlines 
on Tue. There is a shortwave trough in WNW flow that digs SE from 
the Gt Lakes and brings low pressure thru the mid-Atlc states but at 
this point, guidance seems more bullish on this Clipper type low 
passing well to our south Wed, with the GFS bring the furthest 
north. 

Temperature profiles are considerably cooler, and as such should
see high temperatures run a couple degrees cooler each day. 
Despite it being a dry weather pattern, there are some 
indications of variable amts of cloud cover, and that introduces
more uncertainty on low temps. Highs project as cooler than 
normal and lows around seasonable or perhaps even above normal 
if we can sustain more cloud cover at night although there are 
no significant temperature anomalies this period. 

Friday: 

Most of the global NWP show another progressive Clipper type system 
moving into the Northeast from the Gt Lakes region on Fri, although 
typical uncertainties exist regarding its amplitude and timing. 
After a soggy start to this forecast period, this Friday clipper 
system offers our next chance for precip - and could be in the form 
of snow at least at outset, although Clippers ordinarily are not 
significant precip producers. Still time to iron out timing and 
strength details.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

06z TAF Update: 

Today: High confidence in trends but lower on exact timing. 

Widespread IFR in fog slowly improves to MVFR 12z-15z and then
VFR cloud bases 15z-19z and thereafter. Just spotty light
rain/drizzle through about 12z, then a mainly dry day. Light SSW
becomes WSW. 

Tonight...High confidence.

VFR cloud bases and dry weather this evening. Then around
midnight and thereafter, MVFR conditions overspread the area
with IFR by 12z Sunday, along with light rain. Light WNW wind in
the evening becomes NE 10-15 kt by 12z Sunday. 

Sunday...high confidence. 

Widespread IFR in rain with areas of LIFR across the high
terrain of MA/CT. ENE 10-15 kt with gusts up to 20 kt across
southeast MA.  

KBOS Terminal...High confidence in TAF trends, lower on exact
timing.

IFR this morning will improve to MVFR 12Z-15Z then VFR cloud
bases 18z-21z and beyond. Other than some spotty light
rain/drizzle early this morning, mainly dry after 12z. Light SSW
winds this morning, WSW this afternoon. 

KBDL Terminal...High confidence in TAF trends, lower on exact
timing. 

IFR this morning will improve to MVFR 12Z-15Z then VFR cloud
bases 15z-18z and beyond. Other than some spotty light 
rain/drizzle early this morning, dry after 12z. Light SSW winds
this morning, WSW this afternoon. 

Outlook /Sunday Night through Wednesday/...

Sunday Night: Mainly MVFR, with local IFR possible. Breezy. RA.

Monday: Mainly VFR, with areas MVFR possible. Breezy. Chance
RA.

Monday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance RA.

Tuesday: VFR. Breezy. 

Tuesday Night: VFR. 

Wednesday: 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...High confidence. 

A low pressure tracks through the Ohio Valley and high pressure
remains well offshore, continuing a SW flow across the MA/RI 
waters. Periods of rain and fog will lower visibilities. Seas 
are 1 to 3 feet. 

Saturday and Saturday Night...High confidence.

A weak low pressure tracks across southern New England, morning
fog with lower visibilities are followed by area of light
drizzle otherwise a mainly dry weather and light winds for the 
MA/RI waters. Seas increasing 2 to 4 feet, may approach 5 feet
for the waters south of Block Island and Nantucket Saturday
evening. Held off on a Small Craft Advisory for now. 

Outlook /Sunday Night through Wednesday/...

Sunday: Winds less than 25 kt. Seas up to 5 ft. Rain. 

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Rain. 

Monday: Low risk for Small Craft Advisory winds with local
gusts up to 30 kt. Areas of rough seas. Chance of rain. 

Monday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain. 

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain. 

Tuesday Night: Winds less than 25 kt. Slight chance of rain. 

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&