Area Forecast Discussion
National Weather Service Boston/Norton MA
1227 PM EST Tue Nov 29 2022

.SYNOPSIS...
High pressure will result in plenty of sunshine with light winds and 
seasonable temperatures today.  A strong cold front approaches 
Wednesday bringing a period of heavy rain along with strong to 
potentially damaging wind gusts late Wednesday into Wednesday 
evening. Windy conditions continue on Thursday along with chilly 
temperatures. A low pressure system brings our next chance for some 
rain for Saturday with dry but blustery weather returning on
Sunday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
10AM Update

Latest GOES16 visible satellite images reveal a deck of 
STRATOCU filling in across most of eastern MA and portions of 
the outer Cape. Additional cloudiness can be seen over western 
MA and CT. Only areas seeing abundant sunshine right now are 
central MA, RI, and northeast CT. Biggest change in the forecast
with this update was to reflect the increasing cloudiness 
across eastern MA. This is having an impact on the temperature 
forecast as well as a lack of sunshine will suppress high 
temperature potential. Thus, have lowered the high temperature 
forecast this afternoon as well. 

 &&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
700 am update...

Very cold start to the day this morning with temperatures
sitting in the low to mid 20s at 7 am. Fortunately winds are
very light thanks to high pressure overhead. No significant
changes necessary with this morning's update. 

Previous Discussion...

Highlights...

* Dry & seasonably chilly tonight
* Period of Heavy Rain & strong wind gusts late Wed into Wed evening

Details...

Tonight...

High pressure moves east of the region tonight. Initially...the dry 
airmass in place coupled with light/calm winds will allow for temps 
to quickly drop at sunset. Many locales should quickly drop into the 
upper 20s and lower 30s...but we should see temps level off and even 
rise a bit toward daybreak particularly along the immediate coast. 
This in response to strong shortwave moving east into the Great 
Lakes. This will result in low clouds overspreading the region 
particularly toward daybreak. By sunrise...much of the immediate 
coast should see temps already into the 40s given increasing 
southeast flow off the relatively mild ocean.

Wednesday and Wednesday night...

Strong shortwave and associated cold front will be moving across the 
eastern Great Lakes Wednesday morning. In response...increasing 
southerly LLJ may result in a few spot warm advection showers or 
perhaps even a touch of drizzle Wednesday morning. However...much of 
Wednesday morning may end up just cloudy with temps rising through 
the 40s and into the 50s along the coastal plain. We will break 
things down more later Wednesday and Wednesday evening with a period 
of heavy rain and strong to potentially damaging wind gusts are 
possible.

1) Period of Heavy Rainfall Later Wednesday into Wednesday Evening:

The forcing for ascent will rapidly increase Wednesday afternoon 
from west to east. This will allow for a widespread soaking rain to 
overspread the region roughly between noon and 4 pm. The southerly 
LLJ becomes quite robust late Wednesday into Wednesday evening...3-4 
standard deviations above normal. This strong forcing coupled with 
deep low level moisture will result in a brief period of heavy rain 
into the first half of Wednesday evening. This should result in 
rainfall amounts generally on the order of 0.50 to 1 inch...although 
localized higher totals can not be ruled out. This system is quite 
progressive...so other than brief typical ponding of water on some 
roadways no significant flooding issues are expected.

2) Period of Strong to Potentially Damaging Wind Gusts :

The main concern though will revolve around the expected period of 
strong wind gusts late Wednesday into Wednesday evening. The high 
resolution guidance indicates a southerly LLJ at 850 mb peaking at 
around 80 knots. It is always quite uncertain in these southerly low 
level inversion cases how much of this wind will be able to mix 
down. But a conservative ball park figure can often be roughly half 
of the 850 mb jet. A further look at the model soundings reveal that 
the inversion will become quite limited...particularly if temps can 
push into the upper 50s to near 60 degrees like much of the high 
resolution guidance indicates. This threat would also increase if 
some sort of fine line can develop and this is hinted at by some of 
the CAMs. Therefore...we think that a period of southerly wind gusts 
of 40-50 mph will occur particularly across RI/Eastern MA where 
climatology typically favors. So a few gusts up to 55 mph are 
certainly possible. Given this coupled with heavy rain...power 
outages are possible. 

In addition...the model guidance indicates a rapid rise/fall couplet 
behind the cold front late Wednesday into Wednesday evening which is 
also often supportive of a brief period of strong to perhaps 
damaging wind gusts. This coupled with temps dropping rapidly into 
the upper 30s and 40s. A second brief round of 40 to 55 mph wind 
gusts are expected behind this front. 

We opted to issue a Wind Advisory for Central/Eastern MA and 
RI...but there is a pretty good shot these headlines may have to be 
expanded across western MA & CT in later forecasts. Strongest of the 
winds look to occur roughly between 3 pm and 9 pm Wednesday evening.

3) Dry But turning Chilly & Still Windy Late Wednesday night:

Strong westerly winds will result in dry but chilly weather working 
into the entire region by late evening. West to northwest wind gusts 
of 25 to 40 mph will persist for much of the overnight hours. The 
wind will keep overnight low temps in the upper 20s to middle 30s 
across much of the region. Wind chills will drop into the upper 
teens to the middle 20s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Highlights...

* Strong winds continue on Thursday, diminishing overnight

* Dry and quiet until our next system arrives for the weekend 
  bringing another round of rain and strong winds Saturday

* Temperatures increasing through Saturday before returning to 
  normal, but no big cool down in sight through early next week. 

Details...

Thursday and Friday...

One more day of strong winds is in store on Thursday thanks to a 
very well mixed boundary layer in the cold, post-frontal airmass. 
Cold, dry west-northwest flow brings in dewpoints in the low 20s as 
surface temperatures top out in the 30s and low 40s (about 15 
degrees colder than Wednesday). It will, however, feel about 10 
degrees colder due to gusty post frontal winds, lasting through the 
day. As the trough lifts out of New England, replaced by a building 
ridge of high pressure, the lingering low level jet will easily mix 
down to the surface in the cold air advection pattern. BUFKIT 
soundings indicate a well mixed boundary layer up to 850 mb where 
winds will be blowing 35 to 45 kts. This will allow for gusts 30-40 
mph, as high as 50 mph. Winds continues through sundown after which 
the boundary layer cools and high pressure moves overhead reducing 
the pressure gradient and strong low level winds. This may allow for 
some radiational cooling if things decouple quickly enough. 

Friday will be much quieter beneath surface high pressure and a mid 
level ridge. Placement of the high to the east will turn winds out of 
the south and southwest initiating warm advection which brings highs 
back toward normal, in the mid to upper 40s. 

Saturday through Monday...

For the weekend, Saturday looks to bring another round of rain and 
wind as a shortwave digs into the Great Lakes, crossing New England 
early on Sunday. A depending surface low will lift northwest of 
southern New England dragging a series of fronts through the region. 
With the passage of this system comes another strong, 45-55 kt low 
level jet which, with surface temperatures in approaching 60 degrees 
on Saturday would readily mix down as strong gusty winds. It's too 
soon to nail down details on timing or placement of strongest winds 
and heavy rain, but at this point Saturday looks like an unsettled 
day followed by a drier and colder Sun/Mon under high pressure.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels:

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


18Z TAF Update...High Confidence

Through 00Z

VFR with SCT to BKN STRATOCU deck from 030-040 for the rest of
the afternoon. Sky conditions are more on the CLR to SCT side 
across central MA, RI, and the Islands. Winds somewhat light and
variable under high pressure, but should see winds across the
eastern area take on more of an easterly component this
afternoon.

Tonight...High Confidence

VFR for most of tonight with patchy MVFR ceilings as cloud 
bases range from 035 to 045. May see some 025 ceilings spread
into the western areas as head approach day break.

Tomorrow and Tomorrow night...High Confidence in trends with 
moderate confidence in timing. 

MVFR ceilings overspread the region tomorrow morning with patchy
areas of IFR, especially over the high terrain.Expect showers 
to develop from west to east starting mid to late morning. Winds
strengthen dramatically ahead of an approaching cold front with
gusts 

Rainfall intensifies around 00Z when a surface cold front pushes
through the region with wind gusts up to 40 knots beginning
after 18Z. Cold front pushes through the region around 00Z with
potentially heavy rainfall and gusty winds. Winds will be
south/southeast ahead of the front and WNW behind the front.
Expect rainfall to be out of the area entirely by 06Z Thursday.
Gust westerly winds persist through Thursday.

BOS TAF....High confidence
BDL TAF... High confidence

Outlook /Thursday through Saturday/... 

Thursday: VFR. Strong winds with areas of gusts up to 40 kt. 

Thursday Night: VFR. Windy with gusts up to 35 kt. 

Friday: VFR. 

Friday Night: VFR. Breezy. 

Saturday: Mainly VFR, with areas MVFR possible. Windy with
gusts up to 30 kt. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Highlights...

* Gale Warnings all waters later Wednesday through Thursday

Today and Tonight...High Confidence.

Large high pressure builds over the waters today and moves east of 
the region tonight. This should result in lingering small craft seas 
diminishing across the outer-waters this morning. Otherwise...winds 
and seas will remain below small craft advisory thresholds through 
tonight.

Wednesday and Wednesday night...High Confidence.

Strong cold front approaches Wednesday and quickly moves across the 
waters Wednesday evening. Southerly LLJ strengthens ahead of this 
cold front allowing for a period of south wind gusts of 35 to 45 
knots late Wednesday afternoon/early evening...which will then shift 
to the W behind the front. Gale Warnings are posted for all waters 
and will continue through Thursday as strong cold advection develops 
over the relatively mild waters. 

Outlook /Thursday through Saturday/...

Thursday: Strong winds with gusts up to 35 kt. Rough seas up to
10 ft. 

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas. 

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

Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 20 kt. Seas locally approaching 5 ft. 

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Wind Advisory from 1 PM Wednesday to 1 AM EST Thursday for 
     MAZ004>007-012>024-026.
RI...Wind Advisory from 1 PM Wednesday to 1 AM EST Thursday for 
     RIZ001>008.
MARINE...Gale Warning from 1 PM Wednesday to 7 PM EST Thursday for 
     ANZ230>237-250-251-254>256.

&&