Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 270538
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
138 AM EDT Sat Jul 27 2024

.SYNOPSIS...
Dry and seasonably warm conditions will continue through the
weekend. A weak low pressure system over the ocean could bring 
some light rain to areas on Monday. It then turns much more 
humid Tuesday through Thursday of next week, with daily chances 
at showers and thunderstorms. Temperatures through the workweek 
will be around or slightly above normal.

&&

.NEAR TERM /UNTIL 7 AM THIS MORNING/...
9:30 PM Update:

No changes made to the forecast with this update. Temperatures
have dropped rapidly in the last hour or so with widespread 60s
being observed away from Urban centers. Temps will continue to
fall into the 50s and low 60s region wide. 

715 PM Update: 

No significant changes needed with this update. 

Forecast looks to be holding up pretty well so far, with a
pleasant/tranquil evening ahead. Will mention that we're now
seeing quite a bit of hazy skies associated with high-altitude
smoke well aloft stemming from the wildfires burning in west- 
central Canada. This is seen really well in GOES True-Color
satellite imagery and recent CEF METAR remarks also indicate 
smoke above 25,000 ft. Fortunately no adverse impacts from this
aside from a potentially more vibrant/redder sunset. 18z HRRR-
Smoke model indicates a potential repeat performance for 
tomorrow under NNWly flow aloft. But again, no adverse impacts 
are expected with modeled near surface smoke concentrations 
being nil. 

Aside from that, lighter northerly winds expected tonight with
dry weather prevailing. Lows in the mid 50s to lower 60s, with
low-mid 60s for the cities and Cape Cod/Islands.

Previous discussion:

quiet mid-summer weather across the region. Just some scattered
shallow daytime heating cumulus clouds. The slightly gusty
northwest winds are diminishing, and this is allowing the sea
breeze to develop across eastern coastal areas of Massachusetts.
Temperatures are seasonable, with lots of low to mid 80s. For
the rest of today, what you see is what you get. Get out and
enjoy -- unless you are a fan of cold and snow...and in that 
case, it's going to be awhile. Clouds quickly dissipate with
sunset so it's setting up to be clear tonight. With afternoon
dewpoints in the 50s in most inland areas, that gives us a rough
idea of the potential lows temperatures. Given decent
radiational cooling expected, did lean toward the cooler of the
guidance and blended in the NBM 10th percentile data and the 
MOS guidance. Could be a touch of fog in typical spots (like
parts of the CT River Valley) and around some lakes and ponds.
Not expecting anything widespread however.

&&

.SHORT TERM /7 AM THIS MORNING THROUGH 6 PM SUNDAY/...
245 pm update...

Synoptically we are under a high pressure "big bubble no 
trouble" pattern. For the most part, Saturday will look and feel
very similar to today. Expect daytime cumulus to develop as well
as sea breezes along the coast. With 850 mb temperatures running
in the 13-15C range, that would suggest temperatures here on the
ground should be in the 28-30C (low to mid 80s) range. Coolest
will be in the higher elevations as well as where we will see
the sea breezes along the immediate coast and Cape and Islands.
Saturday night should be a near repeat of tonight. Again trended
toward some of the cooler temperature guidance, and painted in
low temperatures in the mid to upper 50s -- though urban areas
should stay in the 60s. Could there be some more patchy fog
Saturday night? Sure, why not. But with a generally dry 
atmosphere, not expecting it to be widespread.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
245 pm update...

Highlights: 

* Dry Sunday with seasonably warm temperatures, though with 
  increasing cloud cover. 

* Upper low moving near or over Southern New England Sunday night 
  into Monday brings cloud cover and light rain showers to the 
  region. 

* Turns much more humid Tuesday thru Thursday with daily chances for 
  showers and thunderstorms, although won't be raining the whole 
  time. Temperatures around or slightly above normal, but nightime 
  lows will be above normal.
  
Details:

Sunday into Monday: 

Initial ridge of high pressure to be in place over Southern New 
England on Sunday. However the main weather feature of interest is 
an upper level low and surface reflection expected to be located 
somewhere near or just south of 40N/70W on Sunday. This feature is 
expected to meander NW later Sunday evening into Monday into 
Southern New England or the lower Hudson Valley, as it merges/phases 
with a slow-moving mid/upper level trough over the Gt Lakes region. 
There remains considerable uncertainty in the initial placement of 
the upper low and its exact track through the Northeast, and 
analysis of 12z ensembles don't offer much insight into a preferred 
track. The ECMWF remains on the western end (more into northeast 
NJ/lower Hudson Valley); the GFS and Canadian are somewhat similar 
in low track over the eastern coast of Southern New England. While 
the details are still quite hazy, 

It looks as though Sunday and even into later-Sunday should be dry, 
though the latter part of Sunday should feature increasing cloud 
cover expanding northwestward associated with the upper low's 
landward approach. Thus for Sunday, we should be able to eke out one 
final nice day before our weather pattern turns cloudier and more 
unsettled. Dry weather with highs on Sunday in the 80s, on the upper 
end of that range over interior CT/MA further removed from advancing 
cloud cover, and in the lower 80s for southeast New England with 
more of a canopy of cloud cover to temper heating to an extent. Will 
be turning a touch more humid as well but excessive humidity isn't 
expected.

Increasing clouds and shower chances then develop soonest over the 
Cape and Islands Sunday evening, then expanding northwestward into 
the overnight and into Monday timeframe. Rain shower chances should 
initially be favored for eastern/coastal areas, then gradually 
expanding into the interior as we move into Monday. Precipitable 
water values associated with this upper level low are not expected 
to be climatologically anomalous, with values around an inch to inch 
and a half; correspondingly, PWAT standardized anomalies are around 
0 sigma. Thus not expecting any significant downpours from any rains 
which develop, and it is not likely to be raining all of Monday 
either. Sunday night's lows should be a bit warmer than prior 
nights, in the mid 60s, with highs on Monday in the upper 70s to mid 
80s areawide due to cloud cover and rain chances.

Tuesday through Thursday: 

Upper level low from late Sunday/Monday to either phase with or move 
northward into northern New England early on Tue. However this 
period features continued mostly cloudy and unsettled weather with 
daily chances at showers and thunderstorms associated with the slow-
moving mid/upper trough over the Gt Lakes. There is a more favorable 
southerly influx of deeper moisture in this period, with PWAT 
standardized anomalies around 1 to 2 standard deviations above 
normal (1.5-2 inch PWAT values). So this will lead to elevated 
humidity levels (e.g. dewpoints in the upper 60s to mid 70s), but 
also support potential for downpours in showers or thunderstorms 
which develop. Couldn't rule out showers or t-storms anywhere in 
this period of time, and it likely will not be raining the whole 
time, but interior MA and CT stand a slightly better chance than 
eastern MA/RI closer to the upper level feature. Couldn't really 
provide much specificity given uncertainties, so kept a rather broad 
brush to PoPs close to NBM values for this period. 

With still a good amt of cloud cover around, high temperatures 
should run close to climatology or slightly above (highs mid 80s 
Tue/Wed, into the mid to upper 80s on Thurs), with above normal low 
temps in the upper 60s to mid 70s Tue thru Thu nights. Heat indices 
should remain below heat advisory criteria, although we could 
have a few locations reach the mid to upper 90s for heat indices
late in the workweek.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

06Z TAF Update: 

Through Sunday: High Confidence

VFR with light WNW/NW winds across interior southern New
England. Climatological coastal sea breezes very likely between
15-16Z as winds shift more easterly. Winds become SE to SSW
after sunset this evening. 

Low probability of marine stratus/fog over the Islands after 06Z
tonight. VFR returns early Sunday morning. Tracking low pressure
that will advect increasing clouds over the region Sunday but
anticipate conditions will remain VFR. Winds will shift to the
east as low pressure approaches, any may gust as high as 25kt
across the Cape and Islands by 00Z Monday. 


KBOS TAF...High confidence in TAF. VFR. Climatological seabreeze
likely today between 15-16Z. Winds shift to the SE after 00Z
tonight. 

KBDL TAF...High confidence in TAF. VFR thru the period. Light
north/northwest winds. Winds shift more southerly after 00Z
Sunday. 

Outlook /Sunday Night through Wednesday/...


Sunday Night through Monday: VFR. Slight chance SHRA.

Monday Night through Tuesday: Mainly VFR, with local MVFR
possible. Slight chance SHRA, isolated TSRA.

Tuesday Night: VFR. Slight chance SHRA, isolated TSRA.

Wednesday: Chance SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

230 pm update...

Overall high confidence through the weekend. 

Ridge of high pressure will be across the region through
Saturday night. Thus winds should be 15kt or less, and in fact
barely over 10kts in many areas. There will be local onshore sea
breezes on Saturday. With the light winds and no significant
swell energy coming into the region, wave heights will remain 3
feet or less. 

Outlook /Sunday Night through Wednesday/...

Sunday: Winds less than 25 kt. 

Sunday Night: Winds less than 25 kt. Chance of rain showers. 

Monday: Winds less than 25 kt. Slight chance of rain showers. 

Monday Night through Tuesday: Winds less than 25 kt. Seas
locally approaching 5 ft. Slight chance of rain showers,
isolated thunderstorms. 

Tuesday Night: Winds less than 25 kt. Slight chance of rain
showers. 

Wednesday: Winds less than 25 kt. Slight chance of rain
showers, isolated thunderstorms.

&&

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

&&

$$

SYNOPSIS...Loconto/Nash
NEAR TERM...Loconto/KS/Nash
SHORT TERM...Nash
LONG TERM...Loconto
AVIATION...KS
MARINE...Loconto/Nash