Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 131949
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
349 PM EDT Tue Oct 13 2026

.WHAT HAS CHANGED...
Updated for the aviation section.

&&

.KEY MESSAGES...

- Showers through the evening, perhaps a rumble of 
  thunder.

- Mild and breezy day Wednesday. Low chance for an isolated shower 
  or sprinkle in the afternoon. Dry conditions Thursday with 
  seasonably cool temperatures.

- Low pressure system expected to bring rain Friday into early Saturday.
  Gusty northwest winds and below normal temperatures expected 
  Saturday behind the system. 


&&

.DISCUSSION...
KEY MESSAGE 1...Showers through the evening, perhaps a rumble of 
thunder.

A fairly dynamic system, the bulk of which is passing by well to our 
north, will be the forcing mechanism to bring the chance of showers, 
and perhaps a brief rumble of thunder, to portions of the area late 
this afternoon through late evening. Hi-res CAMs are not capturing 
very well the cluster of stronger convection across parts of Ontario 
into central New York, so confidence in the evolution and timing of 
any showers that make it into southern New England is on the lower 
side. The convection appears to be primarily elevated, and mid-
level lapse rates across our area are progged to be marginal to 
maintain some of the activity. With no specific model doing well 
with the current activity, I stuck with the blended guidance 
approach, showing 30-40% PoPs in a general WNW to ESE orientation 
from western MA down to SE MA and the Cape and points north of that. 
Rainfall amounts should be generally 1/4" or less, though up to 1/2" 
is possible, especially across far northern areas closer to the 
VT/NH borders.  Otherwise lots of low clouds, and some fog along the 
coast courtesy of a moist low level southeast flow.  As the evening 
and overnight goes on, the winds will transition to southwest and 
start to bring some drying to the low levels. So after any showers 
move through, we should start to see partial clearing prior to 
sunrise. On the flip side, those clouds will keep low temperatures 
from dropping too much. In fact, some areas might see a slow rise in 
temperatures. 

KEY MESSAGE 2...Mild and breezy day Wednesday. Low chance for an
isolated shower or sprinkle in the afternoon. Dry conditions 
Thursday with seasonably cool temperatures.

A trailing cold front shifts across the region Wednesday with 
surface high pressure slowly building in from the west through the 
day. This will gradually clear out the lower clouds through the 
morning. Model soundings show sufficiently mixed supporting drier 
conditions and breezy westerly winds. Gusts likely range between 20-
30 mph with a locally higher gust in the higher terrain of the 
Berkshires. Westerly, downslope flow combined with 925mb 
temperatures +16-18C will support a warm fall day with highs in the 
70s in many areas. Isolate shower are possible as a weak wave moves 
through in the afternoon, but this will be fairly limited in 
coverage and more likely limited to a sprinkle due to the drier 
lower levels. 

As high pressure settles in further into Thursday, the airmass dries 
out even more. Thursday will likely be dry, although cooler than 
Wednesday. A cooler airmass will have moved in with 925mb 
temperatures around 10C cooler than Wednesday. This will yield 
seasonably cool temperatures mainly in the low 60s and lighter 
northerly winds. 


KEY MESSAGE 3...Low pressure system expected to bring rain
Friday into early Saturday. Gusty northwest winds and below 
normal temperatures expected Saturday behind the system. 

Deterministic and ensemble guidance show a deep northern stream 
shortwave trough push across the Great Lakes and the northeast 
Friday into Saturday. An upper level jet setting up near southern 
New England will provide support for broad synoptic ascent and 
advect a plume of anomalous moisture into the region. This will set 
the stage for a widespread rain. Ensemble guidance ranges amounts 
generally from 0.30 to 0.80". The ECMWF and Canadian still lean 
wetter than the GFS despite its subtle upward trend in amounts. The 
wetter solutions show potential for banded or localized amounts of 
1.0-1.4", likely a result of the additional frontogenetical forcing 
combined with marginal instability. Location of where the bands of 
heavier amounts set up is still uncertain. Rain most likely arrives 
in the Friday morning timeframe, continuing through the evening. 
Most guidance shows this system to be fairly progressive meaning it 
shifts out fairly quickly. The bulk of the rain likely exits late 
Friday night with the pre-frontal trough. There is also an axis of 
instability associated with this trough which may provide enough 
forcing/support for a line of convective showers and perhaps even a 
thunderstorm in the mix. 

In addition, the initial southerly LLJ with this system nudges in 
Friday which if mixed sufficiently, will bring breezy to gusty SW 
winds. Gusts 20-35 mph are possible with potential for gusts up to 
40 for the Cape and Islands and also Block Island. 

A strong cold front pushes across the region by early Saturday 
morning putting the northeast within a classic cold air advection 
pattern with gusty NW winds, cooler temperatures, and isolated 
showers. A NW 30-40 kt 850mb jet pushes into the region Saturday. 
CAA will provide the steeper lapse rates to support deeper mixing 
and thus gusty NW winds. The degree or mixing and strength of the 
LLJ are still less certain this far out, but ensembles show a signal 
for gusts 35-45 mph possible, potentially higher across the coastal 
waters. 925mb temperatures range between -2C to +2C Saturday 
yielding likely the coolest temperatures of the season so far. Highs 
will likely struggle to get out of the 40s in most places. Some of 
the higher elevation points across the Berkshires may struggle to 
hit the 40 degree mark! RH fields show residual moisture within the 
cyclonic flow pattern. This may be enough to support some isolated 
showers. It's a bit too early to say the "S word" just yet(snow) 
with confidence. However, if the timing aligns, a morning flurry 
can't be ruled out in those highest terrain in the northern 
Berkshires. No accumulation expected. Expect a cold night Saturday 
night with high probabilities for non-coastal areas to be at or 
below the freezing mark. Higher elevation locations may drop into 
the mid-upper 20s.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

18z Update

Overall moderate confidence.

Lots of IFR across the region, primarily due to low ceilings. Though 
a few sites are also showing some lower visibilities due to BR/FG. 
Fairly confident that the low clouds will be sticking around for 
most of the night. They will begin to lift and break up as low level 
winds start to transition to the SW.  The wind change will happen by 
06z, with VFR conditions expected to become common after 09z.  Much 
lower confidence on the timing of showers, or perhaps even a brief -
TSRA. Expect the best chances for showers to be across MA, northern 
RI and across the Cape and points northward. Probabilities for 
thunder are fairly low, but not 0. Generally less than 30%. Did keep 
a PROB30 for ORH, but kept the mention out for other locations. 
Figured that it was best to see how the convection across central 
New York evolves as it moves this way.  Any threat for showers will 
end by 03z out across western areas and 07z across the east.

For Wednesday, expecting VFR conditions areawide. Winds will 
transition to W and NW by mid morning. Looks like the potential for 
some gusts 20-25kt developing by mid-day and into the afternoon. 
Can't rule out a g30kt for ORH.  VFR conditions continue Wednesday 
night and into Thursday. 

KBOS Terminal...Moderate confidence. Timing of showers through
this evening and ultimate improvement to MVFR and VFR 
conditions late tonight have up to a couple of hours of error.


KBDL Terminal...Moderate confidence. Expect showers to remain
north of the airport this evening so did not include in the TAF,
however there is a 10-20% chance for -SHRA between 21-01z.

Outlook /Wednesday Night through Sunday/...

Thursday: VFR. Breezy. 

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

Friday: MVFR/IFR conditions possible. Windy with gusts up to
35 kt. SHRA, slight chance TSRA.

Friday Night: Mainly VFR, with local IFR possible. Windy with
gusts up to 35 kt. Chance SHRA.

Saturday: VFR. Strong winds with local gusts up to 40 kt. 

Saturday Night: VFR. Windy with local gusts up to 35 kt. 

Sunday: VFR. Breezy. 

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Thursday...High confidence.

Winds turn SW early this evening as low pressure passes by to the 
north. Expect to see winds increasing to 20-25kt away from the 
coasts. Winds will turn more west/northwest for Wednesday, but still 
continue in the 20-25kt range through mid-day. Winds start to 
diminish later in the afternoon into evening. This will help to push 
waves up to around 5-6ft, especially further offshore.  Thus Small 
Craft Advisories have been continued. Looking toward Thursday, winds 
and seas will diminish as a ridge of high pressure moves across the 
region.

Outlook /Wednesday Night through Sunday/...

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. 

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers. 

Friday: Strong winds with gusts up to 35 kt. Areas of rough
seas. Rain showers, slight chance of thunderstorms. 

Friday Night: gale force winds with gusts up to 40 kt. Rough
seas up to 13 ft. Rain showers likely. 

Saturday: gale force winds with gusts up to 40 kt. Rough seas
up to 13 ft. Chance of rain showers. 

Saturday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 12 ft. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from midnight tonight to noon EDT 
     Wednesday for ANZ231>235-237.
     Small Craft Advisory until 2 AM EDT Wednesday for ANZ250.
     Small Craft Advisory until 8 PM EDT Wednesday for ANZ254.
     Small Craft Advisory from midnight tonight to 8 PM EDT 
     Wednesday for ANZ255-256.

&&

$$

DISCUSSION...Mensch/Nash
AVIATION...Mensch/Nash
MARINE...Mensch/Nash