❰ Current Conditions

NWS Area Forecast Discussion
Area Forecast Discussion
National Weather Service Boston/Norton MA
242 AM EST Mon Nov 29 2021

.SYNOPSIS...
A broad area of low pressure develops east of New England today and 
then lifts into Nova Scotia tonight. This will bring lots of clouds 
and scattered light rain and snow showers. Mainly dry weather 
follows tonight into Tuesday with colder than normal 
temperatures, then a warming trend Wednesday and especially 
Thursday as temperatures trend above normal. Scattered rain 
showers are expected Thursday ahead of a cold front, then cooler
and gusty conditions return Friday into next weekend. 

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
130 AM update...

* Scattered light rain/snow showers

00z models continue to trend drier/less qpf with approaching trough 
today.  This seems plausible as forcing for ascent is weak, as mid 
level trough doesn't take on a negative tilt until moving offshore 
late this afternoon or evening. In addition, lack of deep layer 
moisture (column never completely saturates) accompanying 
trough limits qpf potential. Thus, the trend is for spotty light 
qpf today. In fact, 00z guidance suggest best chance for 
snow/rain showers may be over Cape Cod and Nantucket this 
afternoon, as cold air advection increases on NNW flow behind 
departing offshore low. Near shore water temps in Mass Bay and 
Cape Cod bay are still relatively mild in the low 50s. This will
offer sufficient thermal and moisture fluxes for ocean effect 
showers, with ocean induced CAPEs 500+ j/kg and low level flow 
330-340 degs. Although, boundary layer temps are marginal, so
ptype could be a mix of snow/rain showers across the outer Cape 
and Nantucket. Hence, not much if any impact. Elsewhere, just a
few spotty very light snow showers/flurries or very light rain
showers/sprinkles. Otherwise, much of the day will feature dry
weather. 

Turning colder this afternoon, as cold air advection increases 
across the area along with tightening pressure gradient from 
offshore low developing. Highs mainly 35-40, with low to mid 40s
for Cape Cod and the Islands. Turning colder and blustery later
in the afternoon, as NNW winds increase. As mid level trough
exits offshore late this afternoon, could see some late day
breaks of sunshine on the southwest horizon just before sunset,
especially across CT/western-central MA, possibly into RI.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
130 AM update...

* Colder than normal tonight & Tuesday

Tonight...cold air advection increases across the region in 
response to departing mid level trough. 850 mb temps lower to 
about -8C across the area. Boundary layer flow is more WNW, so 
any snow/rain shower activity over the outer Cape and Nantucket
at 00z, will shift offshore given developing land trajectory. 
Short wave ridging provides dry weather and with surface ridge 
axis advecting west to east overnight, NNW breeze in the evening
will relax 2nd half of the night, providing cold radiational 
cooling where winds decouple. Thus, derived min temps from the 
colder MOS guidance. This supports lows 15-20 in the typically
colder areas, and low to mid 20s elsewhere along with light NW
winds. 

Tuesday...Cold start to the day and not much of a warm up with -8C
at 850 mb and -4C at 925 mb, only supporting highs of
35-40. A modest west wind 10-20 mph will add to the chilly 
conditions. Morning sunshine will give way to increasing 
afternoon clouds as a low amplitude, moisture starved northern 
stream short wave approaches from the west. Weak forcing for 
ascent and model soundings revealing dry layer between 850-750 
mb, likely only yields a few flurries in the afternoon. 
Otherwise dry, cold weather prevails.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Highlights...

* Warming up Wednesday and Thursday before a cold front 
  brings cooler weather Friday into the weekend

* Gusty post frontal winds possible on Friday

* Showers likely on Thursday into Thursday night

Details...

A fairly low amplitude pattern continues much of next week featuring 
a persistent west coast ridge / east coast trough. Over New England 
flow will be quite zonal, save for a brief trough passage around 
Thursday. Thus, looking at rather benign and quiet weather for much 
of the period. The main feature to focus on in the extended will be 
a 500 mb trough and surface low which cross northern New England 
Thursday night, dragging a cold front through southern New England 
during the day on Friday. There remains some uncertainty as to how 
quickly the system moves in but isentropically forced rain showers 
may move in as early as Thursday morning with further forcing for 
ascent from a 40-50 kt low level jet and approaching cold front. 
Friday the cold front moves through and dries things out, but brings 
potential for some strong winds as cold advection promotes 
efficient mixing of the boundary layer. Zonal flow then continues 
into the weekend allowing for potential of periodic unsettled 
weather. 

Temperatures will be on the upswing Wednesday into Thursday as warm 
air is pulled north ahead of the incoming shortwave. This brings 
highs into the upper 40s on Wednesday and as warm as the mid 50s for 
southeast MA and RI Thursday; that's about 5 degrees above average 
for early December. Friday temps come back down behind the cold 
front and no big warm ups are on the horizon. 


&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent.

0630z update...

Today...High confidence.

Marginal VFR/MVFR conditions, trending toward VFR this
afternoon. Mainly dry conditions, other than spotty light
rain/snow showers. Precip then shifts toward Cape Cod and 
Nantucket this afternoon, as winds shift to the NNW and increase
10-20 kts. 

Tonight...High confidence.

VFR and dry weather with winds shifting from the NNW to the 
WNW, and speeds diminishing from 10-20 kt to 5-10 kt.

Tuesday...high confidence.

VFR, dry weather and light WNW winds. Slight chance of scattered
snow flurries. 

KBOS TAF...high confidence. Other than light and spotty 
rain/snow showers, mainly dry weather prevails. 

KBDL TAF...high confidence. Other than light and spotty
rain/snow showers, mainly dry weather prevails especially this
afternoon. 

Outlook /Tuesday Night through Friday/...  

Tuesday Night through Wednesday: VFR. Breezy. 

Wednesday Night: VFR. Breezy. Chance SHRA, slight chance SHSN.

Thursday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA.

Thursday Night: Mainly VFR, with local MVFR possible. Windy
with areas of gusts up to 30 kt. Slight chance SHRA.

Friday: VFR. Windy with areas of gusts up to 30 kt. 

&&

.MARINE...
Forecaster Confidence Levels.

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

130 AM update...

Today/Tonight/Tuesday...high confidence.

Weak low pressure develops over Georges Bank today, then tracks
northeast into Nova Scotia tonight. Light NNW-NNE winds this
morning increase to 10-20 kt this afternoon, as offshore low
slowly strengthens. Good vsby with only light spotty rain/snow
showers. Winds diminish tonight and Tue as weak high pressure
builds across the waters from west to east. NNW winds shift to 
the west. Mainly dry weather prevails along with good vsby. 

Outlook /Tuesday Night through Friday/...

Tuesday Night through Wednesday: Winds less than 25 kt. Seas up
to 5 ft. 

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

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain showers.

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance
of rain showers. 

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 10 ft. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 1 PM this afternoon to 7 AM EST 
     Tuesday for ANZ232-254>256.
     Small Craft Advisory from 6 PM this evening to 7 AM EST 
     Tuesday for ANZ250.

&&