Old Res Weather

Lexington, Massachusetts, USA

35°F

2/16/2025 7:17pm

Lexington Conditions: Mist, Overcast
Temperature: 35.1°F / 1.7°C
Dew Point: 32.4°F
Relative Humidity: 90%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 29.00 in Falling Slowly
Visibility: 2 miles
Rain Today: 0.01 in
UV Index: $VPuv None

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 210749
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
349 AM EDT Fri Aug 21 2026

.WHAT HAS CHANGED...
No significant changes to the forecast.

&&

.KEY MESSAGES...

- Cooler than normal temperatures today with steady rain most 
  likely towards eastern MA.

- Wet and unusually cool for the weekend.

- Drier and warmer to start next week.

&&

.DISCUSSION...
KEY MESSAGE 1...Cooler than normal temperatures today with steady 
rain most likely towards eastern MA.

Weak low pressure currently centered south of Long Island is 
expected to slowly shift northeastward today. As it does, eastern 
MA, particularly in SE MA, Cape Cod, and the Islands, will likely 
see a continuation of steadier rain. There remains a consistent 
sharp gradient that starts in the northern portion of the south 
shore, continues along I-95 to the RI border, then along the 
northern borders of RI and CT where expected rainfall totals drop 
from around 0.5" to around 0.3" to the NW, diminishing heading 
further north. The NAM once again appears to be an outlier with 
regards to totals, as the other models trend more towards an 
additional 0.1" or less towards Boston and north and west, then up 
to an additional 0.25"-0.5" towards the Cape, SE MA, and RI. The 
latest HREF PMM has also kept the footprint of higher totals to SE 
MA, Cape Cod, the Islands, RI, and along the south coast. With 
persistent cloud cover and resultant surface cyclonic flow from the 
low pressure, onshore winds will keep the region feeling much cooler 
than normal for late August. Highs today will likely only get to the 
low to mid 70s in the eastern part of the region, with coastal areas 
possibly being cooler. Towards the interior, not much in the way of 
additional precipitation is expected, though cloudier conditions are 
still expected given this pattern. Temperatures there may get into 
the upper 70s, particularly in the CT River Valley.

Rain should become much lighter going into tonight. Onshore winds 
continue, though may start pivoting more northerly as the low 
continues northeastward. Lows will generally be in the 50s for much 
of the interior and the 60s further east.

KEY MESSAGE 2...Wet and unusually cool for the weekend.

The low pressure to our south will continue tracking NE heading into 
Saturday. The cold front associated with it will likely stall and 
linger over and around our eastern coastline, possibly crossing 
right through the Cape. With the front just staying put, the more 
overcast and onshore flow would persist into Saturday. Slight 
discrepancies still exist within the model guidance regarding the 
low's exact location, but the general consensus is that it should be 
just offshore of Nantucket sometime Saturday morning. The NAM has 
this low tracking further to the northeast at a faster pace than the 
other models, while the Canadian and the RAP have it tracking much 
slower, still sitting just south of Long Island by that same time. 
As the day goes on, the low is expected to track more north and 
could reach downeast Maine by Saturday night.

The synoptic story for the weekend remains generally unchanged; a 
much more amplified trough with strong cyclonic flow overhead moves 
closer from the Great Lakes Saturday into Sunday. This set up in 
conjunction with an anomalous moisture plume containing PWATs 
approaching 2.0" favors more widespread rainfall across the region 
for the weekend. NAEFS guidance indicates specific humidity and PWAT 
values up to around 2 standard deviations above normal associated 
with this plume, and other guidance shows favorable IVT right over 
much of eastern MA and RI within the same timeframe this weekend. 
Ensembles do have low probs for 1" totals in 24 hours ending Sunday, 
notably towards the Cape and Islands between the ECMWF ensemble and 
the Canadian ensemble. Totals reaching the 1" to 1.5" mark are not 
out of the question.

Temperatures this weekend will likely continue to be below normal 
for this time of year, given the onshore flow and persistent cloud 
cover. Highs will likely top out in the 70s both days, with Saturday 
looking to be the slightly cooler day of the two as Sunday starts to 
see some drier air move in during the day, helping reduce cloud 
cover. Given the continued onshore flow and the cooler temperatures, 
not much in the way of instability is expected to develop. Some 
embedded thunder can't be entirely ruled out, but predominantly 
stratiform rain is expected.

KEY MESSAGE 3...Drier and warmer to start next week.

The front finally shifts offshore as the trough aloft progresses 
east and the surface low exits the east coast area. Post-front, much 
drier air takes hold with more westerly winds, clearing out 
clouds and dropping dewpoints through Wednesday. The base of the
trough tracks directly overhead into Tuesday and heights rise 
behind it as it continues eastward. High pressure dominates and 
high temperatures return to the 70s and 80s.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

06z TAF Update: 

Through 12z...Moderate confidence, especially on the timing of 
sub-VFR conditions.

Latest guidance has trended more optimistically for terminals
aside from the Cape and Islands with regards to the onset of
sub-VFR conditions. More northern terminals could end up seeing
more borderline VFR/MVFR ceilings tonight. However, ceilings 
towards the Cape and Islands will likely deteriorate prior to 
12z this morning. Winds will remain generally N/NE at 5-10 kt.
Lighter -RA becomes more DZ as it exits TAF sites.

Friday and Friday Night...Moderate confidence.

MVFR-IFR ceilings move in through the morning and afternoon, but
could see borderline MVFR/VFR areas take a bit longer to go
down. BDL may even stay VFR, though periods of MVFR are not out
of the question. Very light rain or drizzle towards eastern
MA/SE MA/south coast/Cape Cod & Islands could become a steadier
light rain with periods of more moderate rainfall also likely.
Uncertainty remains regarding just how heavy this round of rain
could end up being, though, along with when exactly it starts
and how long it may last in different areas. At the latest, it
should resume in eastern/NE MA by the nighttime hours. NE winds
continue at around 10 kt with gustier winds to 20 kt possible
for the Cape and Islands.

Saturday...Moderate confidence.

MVFR-IFR as yet another round of rain may impact the area. Exact
timing uncertain during the daytime hours and it should be
lighter before picking up in the afternoon/evening. This timing
is subject to change with future updates. Continued cyclonic
flow will keep winds generally NE to NNE up to 10 kt,
occasionally reaching 15 kt in E MA.

KBOS Terminal...Moderate confidence in TAF. Guidance trended
more optimistically, however, exact timing for onset of sub-VFR
conditions still remains in flux.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday Night: MVFR/IFR conditions possible. Chance SHRA.

Sunday: Mainly VFR, with areas IFR possible. Chance SHRA,
isolated TSRA.

Sunday Night: VFR. Slight chance SHRA.

Monday: VFR. Breezy. 

Monday Night: VFR. 

Tuesday: VFR. Breezy. 

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Saturday...High confidence.

Winds and seas should remain below SCA criterion through
Friday night. Winds shift more NE today and may get up to 
around 20 kt over the southern waters. Elsewhere, winds 
generally range between 10-15 kt. Winds diminish slightly and 
turn more N Friday night into Saturday morning. Winds over the
eastern waters maintain more of an easterly component to them,
ranging from NE to SE. The southern waters shift more W, ranging
between NW and SW by Saturday afternoon. Seas mainly 3 ft or 
less for all waters with localized spots of 4 ft seas Saturday.

Main issue for mariners is reduced visibilities in rain and
mist Friday night, especially for the eastern waters.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt. Rain showers likely,
isolated thunderstorms. 

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers. 

Sunday Night: Winds less than 25 kt. Local rough seas. Chance
of rain showers, slight chance of thunderstorms. 

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

Tuesday: Winds less than 25 kt. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

DISCUSSION...Hrencecin
AVIATION...Hrencecin
MARINE...Hrencecin