Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 070329
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1029 PM EST Wed Dec 6 2023

.SYNOPSIS...
High pressure maintains dry weather late this week into early
this weekend with temperatures rising to above normal levels. A
strong frontal system has the potential to bring a period of 
steady rain, gusty southerly winds and potential for coastal 
flooding along the southern coastlines later Sunday night and 
into early on Monday. Turning drier by Monday afternoon with a 
brief shot of colder air for Monday night, but temperatures look
to rebound back closer to seasonable levels by next Tuesday and
Wednesday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Continuing to monitor extent of clouds anchored around the
Berkshires. There was a decreasing trend for these clouds, but
it was very slow. Also watching ocean effect clouds impacting
parts of the South Shore, Cape and islands. These clouds should
linger a while longer, really as long as winds stay out of the
N. Expecting winds to become more NW after midnight, so
eventually even these clouds should dissipate to a larger
extent.

Minor tweaks to temperatures this evening. Started out by
matching observed trends. The forecast then gets complicated
with the lingering clouds and light winds. Still thinking we
will not maximize the radiational cooling potential, despite 
the mainly clear skies for some.

630 PM Update: 

While there are still a couple general areas of enhanced
cloudiness - one in the lower CT Valley and the clouds other
across Cape Cod - the trends in many areas per satellite and RH 
cross sections is for decreasing cloudiness. Subfreezing temps
are common across SNE early this evening, and while we expect
some radiational cooling, it's not completely maximized as there 
looks to be enough of a NW wind around for the balance of the 
evening. In addition, while most areas should trend clear, ocean
effect stratocumulus clouds ongoing across Cape Cod as 
mentioned above look to linger for most of if not all of the 
overnight. Thus lows in the upper 20s/low 30s there but 
otherwise, most everywhere should see lows down in the low to 
mid 20s.

Previous discussion:

Light snow has all but ended for eastern MA and only lingering
as a few hit and miss showers in western MA/CT this afternoon.
As the mid level trough axis moves offshore this evening cold,
dry NW winds continue to bring in a much below average airmass. 
Surface temperatures are expected to dip as low as the upper
teens in the highest elevations, closer to the lower 20s 
elsewhere across SNE.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Thursday mid level ridging to our west will direct continued
cool NW flow into the region keeping temperatures on the cold 
side of normal. Highs won't top out higher than mid 30s Thursday
afternoon with a mix of sun and clouds. While there's not much 
moisture to work with, a subtle shortwave and a layer of
moisture at 700 mb will bring increasing mid level clouds during 
the day. By evening heights will be on the rise with the
approaching ridge and moisture exits leaving a clear sky. Given 
that and calm winds with a surface high overhead, it should be a
good radiational cooling night, taking lows into the lower 20s 
and even upper teens in the typically coldest spots.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Highlights: 

* Dry weather Fri thru Sat with warming temperatures to above
  normal levels. 

* Strong frontal system around later Sun night/Mon could bring
  gusty winds, period of steady rain/possible downpours, and   
  possible coastal flooding along the south facing coasts. Still
  some uncertainty on the timing. Stay tuned! Well above normal
  temps Sun and possibly into Mon.

* Brief shot of colder air Mon night but gradual rebound to 
  temperatures on Tue.

Details:

Friday through Saturday Night: 

Gradual warming trend remains indicated in this period as high 
pressure is anchored to our south allowing for warm advection 
and 500 mb heights rise. Skies both Fri and Sat should feature 
mostly sunny to partly cloudy conditions with more clouds the 
further west one goes. Despite some clouds around, dry weather 
is still anticipated with modest SW breezes. Temps rise to 
around or just above seasonable levels on Fri with values in the
mid/upper 40s for highs, and should reach well into the 40s to 
the lower 50s for Sat. 

Sunday into Monday: 

This period is the most active in the long-term portion of the 
forecast - and while there are still some smaller timing
differences that will still need to be nailed down, most of the 
deterministic and ensemble model depictions seem to be keying on
later Sunday night and into the first part of Mon as being the 
most active. We are expecting a strong frontal system coming out
of the OH Valley and Appalachians to move through the Northeast
in that timeframe. This anticipated storm system still has the 
potential to bring several weather-related concerns to Southern 
New England, including a period of steady rains/perhaps a rumble
or two of thunder, breezy to gusty southerly winds, hazardous 
marine conditions and a potential for minor coastal flooding and
possible beach erosion for south- facing coastlines.

While it is not well agreed upon across the model suite, there
are some solutions which show the initiating 500 mb trough
taking on a negative tilt around Sunday night and early on Mon
as the system's surface cold front works its way through. Did
note in response to this added potential for stronger synoptic- 
scale vertical motion, QPF amts in the GFS and ECMWF
deterministic models were quite a bit higher. Deep layer
moisture content also becomes elevated with PWAT standardized 
While there wasn't much in the way of convective instability, 
the meager amt there is could be augmented by the enhanced 
dynamic ascent to support a few rumbles of thunder along the 
frontal zone for the Sunday overnight period. Significant 
flooding problems are not expected but nuisance hydro issues 
could result from any clogged storm drains in the face of steady
rains/local downpours. Frontal boundary looks to clear into the
offshore waters by mid to late morning on Mon, but that too is 
subject to further fine tuning regarding timing. 

Southerly winds stand to be on the increase during the day on
Sun, but the greatest potential for period of enhanced southerly 
gusts is later Sunday night and into early Mon just ahead of the
frontal boundary. Models still depict a robust 925-850 mb
southerly low level jet of 75 to 85 kt Sunday night along the
southern and eastern coastlines. How much mixing we see is still 
unclear but potential exists for wind-related headlines on the 
southern and perhaps eastern coastal areas if we can realize 
enough mixing. Stronger southerly gusts over the water may 
support potential gale or perhaps storm force conditions over 
the waters for Sunday evening into Mon. Finally the strong 
southerly flow may lead to elevated storm surge for south 
coastal MA/RI and could bring the risk for coastal flooding 
concerns and/or beach erosion for those southern coastal RI/MA 
locations. While minor coastal flooding tends to occur more 
often, if peak surge values can coincide with high tide (slated 
for 620 AM Mon AM at Providence) some coastal flooding could 
develop. Little if any notable coastal flooding concerns are 
likely on the eastern coast given southerly flow component.

Above normal temps are favored for this period, especially with
the nighttime lows Sunday night. Highs Sunday should be well
above mid- December climo in the mid 50s to low 60s (climo is
upper 30s to mid 40s), with lows in the 40s to low 50s. Highs on 
Monday are more susceptible to frontal timing although above
normal temps are still favored until frontal passage, and then 
temps then steadily fall upon frontal passage.

Monday Night and Tuesday: 

Rapid clearing takes place Mon night with strong cold advection 
setting shape for a chilly night, though not likely to be as
cold as it could be given enough of a NW breeze. Dry conditions 
remain favored with lows in the 20s.

Dry weather continues into Tue with high pressure to our south.
In addition, it looks as though colder air that moves in on
Monday evening is brief with temps recovering around seasonable 
levels in the upper 30s to low 40s.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

Tonight: High confidence.

VFR for most, although BKN/OVC VFR bases at times at HYA/ACK. N
winds around 5-10 kt, with occasional gusts 18-22 kt over the 
Cape and Islands.

Thursday and Thursday night...High Confidence.

VFR. NNW winds becoming W 5-10 kts. Turning NW 5-10 kts on 
Thursday night. 

KBOS Terminal...High confidence in TAF. VFR. NNW winds trend NW 
overnight, remaining that way until becoming a WNW around 6-8 kt
around ~15-17z Thu.

KBDL Terminal...High confidence in TAF. VFR. Light NW winds will
trend W by Thu ~14-16z with increasing midlevel clouds.

Outlook /Friday through Monday/... 

Friday through Saturday Night: VFR. 

Sunday: Mainly VFR, with local IFR possible. Windy with gusts
up to 35 kt. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

High Confidence.

Expecting winds and seas to diminish for Thursday as high 
pressure moves overhead through Thursday night. 

Outlook /Friday through Monday/...

Friday through Saturday Night: Winds less than 25 kt. 

Sunday: Low risk for gale force winds with gusts up to 35 kt.
Seas locally approaching 5 ft. Chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 11 PM EST this evening for 
     ANZ231>235-256.
     Small Craft Advisory until 10 AM EST Thursday for ANZ254.
     Small Craft Advisory until 7 AM EST Thursday for ANZ255.

&&

$$
SYNOPSIS...Belk/Loconto
NEAR TERM...Belk
SHORT TERM...Belk
LONG TERM...Loconto
AVIATION...Belk/Loconto
MARINE...Belk/Loconto