Area Forecast Discussion
National Weather Service Boston/Norton MA
1016 AM EST Tue Dec 1 2020

.SYNOPSIS...

Blustery and drier conditions today with a few showers 
possible, but more widespread showers moving offshore from Cape
Cod and the Islands early this afternoon. Seasonable 
temperatures return by Wednesday with mainly dry weather 
persisting through Thursday. A few showers are possible Friday 
as a weak disturbance moves through then dry and seasonable 
weather returns Saturday. There is the potential for a coastal 
storm Sunday or Monday but whether that comes to fruition 
remains uncertain.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

10 AM Update...

Cutoff low continues to rotate across the eastern Great Lakes
today. The forecast is generally on track, but have increased
precipitation chances across a good portion of southern New
England. Will see temperatures aloft cooling to -20 to -15 
Celsius at 500 hPa. Given the warmth in the lower levels and any
breaks in the clouds should see isolated to scattered showers
develop as a vort max lifts into western portions of the CWA.
Expect the showers over the Cape and Islands to move offshore by
early this afternoon per HREF/HRRR guidance, which is doing
well based on the current obs. 

725 AM update...

Impressive closed low over western PA with deep trough down to
the SE CONUS. Deep southerly flow across New Eng with PWAT plume
just east of Cape Cod where numerous showers are lifting 
northward over the ocean. Back edge of these showers are
impacting the outer Cape and Nantucket and occasional showers 
should persist here this morning as PWAT plume not in any hurry
to push east as upper low remains to the west. For the rest of
SNE, expect a few showers to redevelop within the cyclonic flow
aloft, especially interior as shortwave energy approaches from 
the west.

Anomalous warmth across SNE this morning with temps upper 50s to
mid 60s. Cold front will be sweeping across the region this
morning so temps will begin to slowly fall later this morning,
but not a big push of colder air as winds shift to SW. Temps
will drop to the mid 40s to lower 50s across SNE by by late 
afternoon.

Core of the low level jet is east of New Eng, but still have
25-30 kt winds in the low levels and much of this should be able
to mix down as boundary layer deepens in response to cold
advection aloft. So a blustery day ahead.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...

Tonight...

Temperatures finally return to closer to normal by Tuesday night 
with lows falling into the 30s. Interior valley locations where 
winds decouple to a greater extent and where more clearing occurs 
could see mid to upper 20s. 

Wednesday...

Closed upper low slowly lifts north into Canada, allowing 
temperatures to return to more seasonable levels for early December. 
850mb temperatures fall to -8C, so with mixing up to that level, 
highs should top out in the upper 30s to mid 40s. There may be some 
snow showers across the interior but with limited moisture, no 
weather impacts are expected and most areas will likely remain dry.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...

Highlights...

* Dry and seasonable Thu and Sat
* A few showers possible Fri, mainly south of the Pike
* Potential for a coastal storm Sun or Mon but low confidence

Wednesday night into Friday...

Mid level trough lifts to the NE Wed night with zonal flow 
developing Thu as high pres builds south of New Eng. Plenty of 
sunshine expected Thu with a modest W/SW wind. Highs mid 40s to 
around 50 degrees.

Next upstream northern stream trough amplifies as it moves through 
the Gt Lakes Fri. SW flow aloft with right entrance region of upper 
jet moving across SNE, but there is some uncertainty with moisture 
availability. GFS is the most robust with rainfall but ECMWF does 
have some light QPF. Best chance of a few showers will be south of 
the Pike. Above normal temps Fri ranging from mid 40s higher terrain 
to lower 50s RI and SE MA. 

Saturday through Monday...

Forecast confidence decreases next weekend into early next week as a 
complex pattern develops with split flow and multiple northern 
stream shortwaves possibly interacting with southern stream energy. 
Which shortwave becomes the dominant feature is unknown with lots of 
moving parts which guidance will struggle to resolve at this time 
range. Lots of spread among deterministic and ensemble guidance on 
possible outcomes with respect to timing, storm track, intensity and 
ptype. Saturday look dry at this time, then potential for a storm 
Sun or Mon but confidence is quite low. Will just carry chance
pops for now.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...

Forecaster Confidence Levels...

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

Today...High confidence.

MVFR to localized IFR to start, gradually improving to VFR by 
the afternoon, but slower improvement over Cape/Islands where
occasional showers will continue through midday. South winds 
turning SW by the afternoon with gusts up to 25 kt possible. 

Tonight...High confidence. 

Mainly VFR with localized MVFR. SW winds 5 to 10 kts across interior 
terminals and 10 to 15 kts for the Cape terminals. 

Wednesday...High confidence. 

Mainly VFR with localized MVFR. SW winds 10 to 15 kts across 
interior terminals and 15 to 20 kts for the Cape terminals. 

KBOS TAF...Moderate confidence in the TAF.

KBDL TAF...Moderate confidence in the TAF.

Outlook /Wednesday Night through Saturday/...

Wednesday Night through Thursday Night: VFR. Breezy. 

Friday: VFR. Breezy. Slight chance SHRA.

Friday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

Saturday: VFR.

&&

.MARINE...

* Gale Warnings for outer waters. Small Craft Advisories for all 
  other waters due to elevated seas. 

Gale warnings continue for all outer waters with southerly gusts up 
to 35 kt possible through this afternoon. Seas remain elevated with 
5-9 ft across inner waters and 10-14 ft across outer waters. Seas 
should fall below 10 ft by Wednesday afternoon.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Rough seas up to 9 ft. 

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. 

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. 

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EST Wednesday for ANZ230>237-
     250-251-254>256.

&&