Lexington Weather

Lexington, Massachusetts, USA

86°F

8/8/2022 7:02pm

Lexington Conditions: Clear
Temperature: 86.4°F / 30.2°C
Dew Point: 73.6°F
Relative Humidity: 66%
Wind: SW Calm, 10-min avg: 2 mph, gust: 15 mph
Barometer: 29.79 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Southeast Middlesex County, MA - Heat Advisory
- SEE ALL NEARBY ALERTS -

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 081447
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1047 AM EDT Mon Aug 8 2022

.SYNOPSIS...

Heat and humidity will continue to be the main weather story 
early this week. Heat Advisories continue through Tuesday. A 
cold front will bring a better chance of showers and
thunderstorms Tuesday. A slow-moving front will favor several 
opportunities for showers and thunderstorms Tuesday night 
through Thursday. Cooler temperatures, but still quite humid 
until this front clears into the coastal waters Thursday night 
into Friday. Seasonable, with much lower humidity Friday into 
next weekend, with dry weather returning.

&&

.NEAR TERM /THROUGH TONIGHT/...

1030 AM Update...

Have adjusted precipitation chances along with weather this
afternoon/evening. Really have dialed back chances away from the
Route 2 corridor. Thinking for most will have isolated
shower/storms with a better shot across the interior per latest
CAM guidance. Given the weak forcing should be more isolated vs
scattered activity wise for most. Have also bumped up temps
toward the 75th percentile of guidance. Given we are essentially
in the same airmass as yesterday would like to reflect similar
temps to yesterday, albeit a bit cooler due to more cloud cover.
Should see highs in the low to mid 90s for most away from the
south coast. Temps top out in the 80s for the south coast. Still
expect oppressive heat with Heat Index values ranging from
95-102, so think the Heat Advisory still looks good.

710 AM Update:

Updated PoP/Wx in a nowcast sense for the southern nearshore
waters from Block Island to Buzzards Bay. Radar and satellite
shows slowly-developing showers with recent KBOX radar scans and
some in-cloud glaciation on GOES satellite day cloud phase RGB 
implying the potential for lightning in some of these cores. 
Seems to be developing in area of approximately 1000 J/kg of 
most- unstable CAPE. MWS in effect for these until 800 AM from 
Block Island to Buzzards Bay/Vineyard Sound as they move ENE.

Also updated PoP/Wx for the rest of the afternoon; still a bit
of an unclear outlook for this afternoon as there isn't any 
apparent or obvious surface convergence zones to support 
SHRA/TSRA development. Mixed signals in guidance and weakly
forced setup also renders a lower-confidence convective forecast.
If we do see storms they may be of less coverage than yesterday
given the lack of any forcing, at least until later in the 
day/tonight when there's an approaching pre- frontal trough that
could spark some activity.

Otherwise, stifling heat and humidity to continue again today
with current temps already into the mid to upper 70s. Heat
indices again to reach into the mid/upper 90s and low 100s.

Previous discussion:

Expecting today to essentially be a repeat of the past few 
days. More heat and oppressive humidity, with a risk for
afternoon showers and thunderstorms. Still dealing with 
relatively weak winds for organizing stronger thunderstorms. 
However, with 1,000-2,000 J/kg most unstable CAPE values, cannot
completely rule out the idea for isolated strong to severe 
thunderstorms.

High temperatures in the lower to mid 90s for most, with the
coolest spots being the highest terrain of north central and
western MA, the south coast of New England, and the islands.

&&

.SHORT TERM /TUESDAY/...

Any lingering showers and thunderstorms should dissipate after
sunset. Although with a stalled frontal boundary a little 
closer to our region, this could take a few more hours than 
previous evenings, especially across the western half of 
southern New England. This front will be even closer Tuesday,
especially once a frontal wave passes by to the east and gets
this front moving south. Expecting a greater chance for some
much-needed rain Tuesday. Given the tropical humidity, local
downpours will be possible.

Have some concerns that some locations towards northern New
England may not quite reach the Heat Advisory threshold due to
increased clouds and a possible earlier start to precipitation.
That said, do not have enough confidence in this timing to
adjust the ongoing Heat Advisories at this time.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Highlights...

* Quasi-stationary front Tue night thru Thurs will focus periods
  of cloudiness and a few opportunities for welcomed rains. Best
  chance at widespread rains Wed night into early Thu. Temps  
  cooler than normal but still quite humid.

* Cooler and much more comfortable humidity levels Fri into the 
  weekend.

* Need to track position of surface cold front offshore but odds 
  favor dry weather for the weekend.

Details:

Tuesday Night through Thursday: 

Quasi-stationary, slowly-southward-sagging frontal boundary in
vicinity of SNE will combine with roughly front-parallel 700-500
mb flow and continued influx of tropical moisture to focus
several opportunities for welcomed rains through showers and
embedded t- storms. Though it's likely it won't be raining for
the whole stretch, continued differences in frontal position 
and more specifically its southward egress through SNE supported
PoP of at least lower Chance level for most of this period. 
Overall severe weather risk appears low to nil given abundant 
cloud cover, some onshore wind component and cooler surface 
temps.

It looks like the period which harbors the best chance at
welcomed rains is later Wed/Wed night into the early Thurs AM 
period, as subtle vort maxima induces weak surface low
development on the frontal boundary and bringing with it a slug 
of beneficial rain, especially near/south of the Mass Pike into 
southeast New England. Seems to be reasonably good consensus in 
this outcome, in spite of how dry we've been, and also supported
by EPS, GEFS and GEPS 24-hour QPF probs of at least 0.5 inches 
that are as much as 70% in the EPS. Lower probs of 24-hr QPF in 
the 1" range in this same corridor. In a convective pattern and 
given the coarser horizontal res of these global models can't 
take QPF at face value but nonetheless favorable probs for 
welcomed rains exist. Given the above, and synoptic pattern 
recognition looking similar to that of the Maddox frontal rain 
regime, opted to increase PoP into the higher Likely to 
Categorical range for Wed night into early Thurs, with PoP then 
diminishing a bit into Thurs aftn. Elevated PWAT values could 
support local downpours. 

Anticipate seasonable to cooler than normal high temps in this  
period, with lows around seasonable levels as well. Highs mainly
mid/upper 70s to lower 80s, lows in the 60s to near 70. However
it still will be quite muggy until the front sags southward 
into the coastal waters. 

Friday into the Weekend: 

Amplification of the western CONUS mid-level ridge is expected
to dig a longwave trough southward from east-central Canada into 
the Ohio Valley/northern Appalachians vicinity. This should
bring a much more refreshing air mass to SNE with lower humidity 
levels and temperatures around seasonable levels. PoP/rain
chances continue to carry some level of uncertainty, but did
note a rather remarkable flip-flop back towards drier weather 
for this period in both global ensemble means and the 00z
deterministic guidance. Though it really didn't have much 12z 
ensemble membership support, the 12z ECMWF/GFS counterparts 
showed a closing-off mid-level trough with developing low 
pressure on the front near Bermuda then pivoting NNW toward 
coastal New England Fri- Sat with a decent slug of rain. The 00z
suite of guidance however came in with a weaker and more 
progressive trough, which shifts the front well offshore into 
the western Atlc and keeps SNE dry with NWly flow. Something to 
monitor, but as NBM is too slow in reducing PoP given what's 
transpired in the 00z guidance, lowered PoP toward borderline 
slight chance/sub- mentionable levels in case today's 12z 
guidance comes back in wetter. Key in that evolution is the 
strength of the trough and if it closes off. Keeping outcomes 
open but given lack of ensemble support for a wetter outcome, 
thinking odds favor drier weather for this weekend.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...

Forecaster Confidence Levels:

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

12z TAF Update:

Today: Moderate Confidence.

Mainly VFR. Brief periods of MVFR in any afternoon showers or 
thunderstorms. SW winds 5-10 kt with gusts up to 20 kt.

Tonight...High Confidence. 

VFR. SW winds 5-15 kts gusting to 25 kts for southeast MA. 

Tuesday...High Confidence.

VFR. Areas MVFR in showers and scattered thunderstorms. SW 
winds 5-10 kts gusting to 20 kts for southeast MA.

KBOS...Moderate confidence in TAF due to uncertainty as to
whether any TSRA makes it to the terminal this afternoon.

KBDL...Moderate confidence in TAF due to uncertainty as to
whether any TSRA makes it to the terminal this afternoon.

Outlook /Tuesday Night through Friday/...

Tuesday: VFR. Breezy. Chance SHRA, slight chance TSRA.

Tuesday Night: Mainly MVFR, with local IFR possible. Breezy.
Chance SHRA, slight chance TSRA.

Wednesday: Mainly MVFR, with areas IFR possible. Chance SHRA,
isolated TSRA.

Wednesday Night: Mainly MVFR, with local IFR possible. SHRA
likely, chance TSRA.

Thursday: Mainly MVFR, with local IFR possible. Chance SHRA,
slight chance TSRA.

Thursday Night through Friday: Mainly VFR, with areas MVFR
possible. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Tuesday...High Confidence.

SW winds 10-20 kt with gusts up to 25 kt. Winds and seas briefly  
diminish early this morning, before picking right back up later
today into tonight. Winds diminish more from N to S Tuesday, as
a cold front slowly approaches from the N.

Outlook /Tuesday Night through Friday/... 

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain showers, slight
chance of thunderstorms. 

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, isolated thunderstorms. 

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

Wednesday Night: Winds less than 25 kt. Rain showers, chance of
thunderstorms. 

Thursday: Winds less than 25 kt. Chance of rain showers, slight
chance of thunderstorms. 

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

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

&&

.CLIMATE...
Record Maximum Temperatures

August 8th:

BOS  96F  [1983]
ORH  94F  [1916]
PVD  95F  [1909]
BDL  98F  [2001]

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Tuesday for CTZ002>004.
MA...Heat Advisory until 8 PM EDT Tuesday for MAZ002>023-026.
RI...Heat Advisory until 8 PM EDT Tuesday for RIZ001>007.
MARINE...Small Craft Advisory until 11 AM EDT Tuesday for ANZ231>235-
     237.
     Small Craft Advisory from 2 PM this afternoon to 7 AM EDT 
     Tuesday for ANZ236.
     Small Craft Advisory from 2 PM this afternoon to 11 AM EDT 
     Tuesday for ANZ250.
     Small Craft Advisory until 8 PM EDT Tuesday for ANZ254>256.

&&

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