Area Forecast Discussion
National Weather Service Boston/Norton MA
403 PM EDT Thu Oct 6 2022

.SYNOPSIS...

Increasing mid to high clouds across southern New England 
tonight. Could see a spot shower across western MA. Another mild
day on Friday, but could have spotty showers and perhaps a 
rumble of thunder or two as a cold front slides through. Cooler 
and blustery conditions for the holiday weekend. Gradual 
moderating trend to temperatures Monday through Wednesday. 
Overall dry weather to prevail Saturday through Wednesday, with 
a frontal passage around Thursday offering the next chance for 
rain chances.

&&

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

Highlights

* Dry and quiet weather for most with increasing mid/high
  clouds. Could have a spot shower or two across western MA.

A shortwave trough will lift from the Mid Atlantic/OH Valley
this evening into New England late tonight. A surface trough
will slide into southern New England ahead of an incoming
low/cold front.

Will see increasing mid/high clouds as the shortwave trough
lifts into the region. Will have increasing
southerly/southwesterly flow which brings PWATs roughly up to
0.8 to 1 inch. Most of region will struggle to saturate in the
lower levels other than western MA. Thinking that western MA
could see a spot shower or two, but given the lack of moisture
it should not amount to much rainfall. 

On top of this will have warm south/southwesterly flow, which
will keep 925 hPa temps in the 14-17 degree Celsius range. Kept
temps at the 50th percentile of guidance given the increasing
cloudiness and seemed reasonable with lows in the 50s tonight.
One potential crux in the forecast is with the increasing
southerly flow and relatively light winds it is not out of the
question there is some patchy fog development. Have backed off
on this given high res guidance has backed off and think the
increasing mid/high clouds keeps radiation fog at bay across
interior locations. Think risk may be higher for some advection
fog along the south coast, but guidance still has mostly backed
off on this. Will be something future shifts need to keep an eye
on in updates.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...

Highlights

* Another mild, albeit breezy day across southern New England on
  Friday. Spotty rain showers and perhaps a rumble of thunder 
  or two during the afternoon as a cold front slides through. 

* Still breezy, but much cooler and drier Friday night into
  early Saturday.

A trough will be situated over eastern Ontario/western Quebec
early on Friday and will lift into central Quebec by late on
Friday. Another trough lifts into the eastern Great Lakes Friday
night, but in between these two features there will be a
shortwave ridge that builds into New England into Saturday. A
cold front will slide into and through southern New England on
Friday and a weak high will nudge in Friday night.

Will have a shot for spotty showers and perhaps a few
thunderstorms across southern New England on Friday as the cold
front slides through during the afternoon. Have leaned toward
the latest CAM guidance, but current forecast may be a bit 
overdone on the shower coverage across the region on Friday. At
this point have some scattered activity across the interior as
the front is moving through. Should see PWATs increase to around
1 inch right along/ahead of the front. The mid/upper moisture is
a bit blah, which could limit the coverage and thunder activity.
Despite this will see a good amount of sunshine ahead of the 
front, which allows low level lapse rates to increase to roughly
7-9 degrees Celsius. Mid level lapse rates per usual look quite
poor, but could see up to 500 J/kg of MLCAPE. Do think any of 
these showers/storms could produce some gusty winds given the 
excellent mixing and a few hundred J/kg of DCAPE. Will see deep 
layer shear increase to around 30-40+ kts, but the 40+ kts is 
along/behind the cold front. Not thinking anything severe at 
this point, but could see some gusty winds. 

Expect another nice day temp wise with readings climbing into
the low/mid 70s for most. Should see temps dropping somewhat
rapidly in wake of the cold front as 925 hPa temps fall roughly
10 degrees Celsius between Friday and Friday night. Expecting
some 20-30 mph gusts ahead of the front, but still will be
breezy in wake of the front overnight. Should see temps fall
into the 30s across the higher terrain and 40s elsewhere. Not
completely out of the question there is some patchy frost, but
confidence not too high given winds generally stay above 5 kts.
If we can decouple faster than frost will be more widespread
across the interior and temps can drop much further.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...

Highlights: 

* Cool, blustery weekend with possible frost during the nights. Slow 
  moderating temperature trends for the holiday weekend into midweek.

* Overall a dry weather pattern Sat thru Wed. Frontal passage around 
  Thurs offers the next best chance for rain chances.

Details:

Overall a dry weather pattern anticipated in this period, with the 
next chance for rain being with a frontal passage around Thurs. 

For the holiday weekend...in the wake of a strong cold frontal 
passage and related post-frontal robust cold thermal advection later 
Fri, a much cooler air mass results in rather blustery conditions 
(WNW gusts up to 20 mph) and a period of below normal temperatures. 
Sat still projects as the coldest of the weekend with 925 mb temps 
down to around +2 to +4C. Will have full sun in the post-frontal 
regime but blustery given shallow mixing. Highs may only reach into 
the mid 50s in interior MA/CT and nearing 60 eastern MA/RI and the 
Cape. Saturday night offers potential for mid 30s lows away from the 
coasts and urban areas; some question if winds can slacken/decouple 
enough for frost development with GFS offering winds between 5-10 
mph. For now shied away from using MOS but if winds can decouple 
fast enough for effective post-sundown longwave radiational cooling 
processes to take place, potential for temperatures supporting frost 
could exist. 925 mb temps warm a degree C or so on Sunday and should 
see temps run upper 50s-low/mid 60s with lows upper 30s to low 40s. 
Overall an outstanding fall weekend if a bit cooler than normal.

For the Monday holiday into midweek...strong 1025-1030ish mb high 
pressure spreads over the mid-Atlantic and Northeast regions Mon and 
Tues, then shifting offshore on Wed. Thus continued mostly clear and 
dry weather. Easing NW winds to turn more S/SW moving into midweek, 
fostering a modest warming trend with highs reaching back into the 
mid to upper 60s by midweek. 

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...

Forecaster Confidence Levels:

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

Through 00Z...High confidence.

VFR conditions everywhere except for the Cape/Islands where MVFR/IFR
conditions linger. Will see gradual improvement late this
afternoon, but may take a bit for ACK to improve. Local
seabreezes along the coast. Elsewhere winds less than 5 kts and
variable in direction. Should become more S/SW toward 00Z. 

Tonight...Moderate confidence.

VFR with increasing mid/high clouds. Could perhaps see a brief
return to MVFR/IFR conditions across the Cape/Islands from
02-08Z. Not out of the question there is some patchy fog
development across the Merrimack/CT River Valley given the light
winds and southerly flow. Not certain on this risk given the
increasing mid/high clouds. A spot shower is possible across 
western MA, but should stay VFR. Winds out of the S/SW less 
than 5 kts.

Friday...High confidence.

VFR with spotty showers and perhaps a thunderstorm or two during
the afternoon as a cold front moves in. Winds start off out of
the S/SW at 5-10 kts and shift to the W/WNW at 5-15 kts and
gusts of 15-25 kts.  

Friday night...High confidence.

VFR with any lingering showers coming to an end during the
evening. Winds out of the NW 5-10 kts and gusts of 15-20 kts
during the evening.

KBOS Terminal...High confidence in TAF. Will see seabreeze end
between 22-01Z and direction shift to the S/SW with speeds
lowering to 5 kts or less.

KBDL Terminal...High confidence in TAF. 

Outlook /Saturday through Tuesday/...

Saturday through Saturday Night: VFR. 

Sunday: VFR. Breezy. 

Sunday Night through Tuesday: VFR. 

&&

.MARINE...

Forecaster Confidence Levels:

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

Tonight...High confidence.

Winds shift to the SW and increase to 10-15 kts after midnight.
Seas 2-4 ft.

Friday...High confidence.

Winds out of the SW at 10-15 kts shifting to the W by late in
the day/evening as a cold front approaches. Could see some 20 kt
gusts during the afternoon. Could see a spot shower/storm late
in the afternoon across the eastern waters. Seas 2-4 ft.

Friday night...High confidence.

Winds shift to the W/NW in wake of the cold front with speeds of
10-20 kts. Could have some 20 kt gusts during the evening. Seas
2-4 ft.

Outlook /Saturday through Tuesday/...

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.

Saturday Night through Tuesday: Winds less than 25 kt. 

&&

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

&&