Lexington Weather

Lexington, Massachusetts, USA

66°F

5/20/2024 3:06pm

Lexington Conditions: Clear
Temperature: 65.8°F / 18.8°C
Dew Point: 56.5°F
Relative Humidity: 72%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 29.99 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 191123
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
723 AM EDT Sun May 19 2024

.SYNOPSIS...
One final day of unsettled conditions before a significant pattern 
shift to drier and warmer weather on Monday. Very warm 
temperatures are expected on Tuesday and Wednesday, with 
temperatures reaching into the 80s, with an outside chance a few
locations see 90 degrees on Wednesday. Humidity levels will be 
on the low side accompanying that midweek warmth. A cold front 
arrives on Thursday with the potential for showers and 
thunderstorms. A drier and more seasonable air mass then filters
in for late in the week into at least the early part of 
Memorial Day Weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
705 AM Update:

Most of Southern New England is socked in with overcast, with
the lowest cloud bases over central and eastern MA, eastern CT
and RI. There isn't much optimism for clouds scattering out for
central and eastern sections of Southern New England, and there
could be periods of drizzle at times. Temps are not likely to go
very far with continued NE winds and the overcast, with highs
around the mid 50s. Into the CT Valley and the Berkshires, 
there are better chances at clouds scattering out and/or 
clearing entirely, where temps would rise into the 70s with 
sufficient clearing. 

Previous discussion:

Overnight guidance continued to perform horribly in identifying the 
presence of moderate to heavy showers along the I-95 corridor that 
seemed to be driven by a SW to NE oriented 925mb jet (~30kt in 
strength) and moisture convergence between 925mb-850mb. Even the 
NAMNest, that was one of the only pieces of guidance that diagnosed 
more widespread, impactful rain on Saturday, struggled to depict the 
nocturnal rain. Am very apprehensive to bite on guidance for today 
that suggests a completely dry day with only very modest changes in 
the synoptic setup; surface high and mid level ridging nudging in 
from the southwest with coastal low moving just ever so slightly 
eastward. So, while not anticipating that Sunday will be as much of 
a washout as we saw for portions of the area on Saturday, do expect 
shower activity will persist through at least the first half of the 
morning before PWATs fall below 1" as low pressure finally draws far 
enough east. Given our tepidness to completely remove PoPs from the 
forecast today, heavily blended the Canadian into the forecast, 
which was the only model that accurately depicted the intensity and 
geographical spread of rain overnight with yesterday's 12Z run. With 
NE flow, do expect shower activity to be remain most widespread east 
of the I-95 corridor, with lesser chances north and west.

With low pressure drawing east, will likely see some clearing across 
the CT River Valley. Cloud cover and rain chances will again drive 
high temperatures, but given pattern of persistence, expecting temps 
to remain in the 50s across eastern MA and much of RI today. With 
more sunshine than yesterday out west, it's possible several 
localities make a run at the low 70s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
While the chance for showers drops significantly overnight, model 
soundings suggest that stratus/drizzle will hang tough across SE 
MA/Cape Cod, and fog, perhaps dense at times, will develop across 
interior southern New England. It will be a seasonable night with 
temperatures dropping into the upper 40s to low 50s.

Surface high nestles safely over southern New England Monday as mid 
level ridging continues to build in intensity and 850mb temps climb 
to between 12-14C by 00Z Tuesday. Given this, well deserved, shift 
in the synoptic setup over southern New England, expecting much more 
sunshine across the region as early morning fog/stratus/drizzle
dissipates quickly through 15Z; though may take until 18/20Z 
across the Cape and Islands. Although temps remain mild aloft, 
boundary layer mixing does not look overly impressive, perhaps 
to ~925mb, so dropped temperatures from what was depicted by the
NBM (80s across the interior) to more conservative high 
temperatures in the mid 70s away from the coast. While flow 
shifts to the south gradually through the day, it will shift 
latest, as late as 22Z, along the coast, so the "synoptic 
seabreeze" will lead to another significant temperature gradient
along the immediate coast, where temperatures will struggle to 
hit 60. In fact, temperatures may not climb out of the 50s on 
the Cape all day!

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights: 

* Very warm temperatures Tuesday and Wednesday away from the 
  southeast coast, with readings into the 80s. Warmest day is 
  Wednesday, and a few locations in the Connecticut and Merrimack 
  Valleys could see their first 90-degree temperature in 2024 on 
  Wednesday! Humidity levels will be tolerable - a "dry heat".

* Cold front moves through sometime on Thursday. Timing of the front 
  is still uncertain but the timing will influence how warm 
  temperatures get and also the potential for thunderstorms, which 
  could be strong.

* Drier with more seasonable temperatures for late in the week into 
  the early Memorial Day Weekend.

Details: 

00z ensembles continue to advertise a significant warm spell for at 
least Tuesday and Wednesday for most of Southern New England. Full 
sun and southwest downsloping breezes, combined with 850 mb temps 
around +13 to +15C should be fairly common on Tuesday with 850 mb 
temps rising about a degree or so on Wednesday. It is likely that 
the Providence to Plymouth corridor on southward to Cape Cod and the 
Islands would be the cooler locations given southwest flow off the 
water, with values in the 70s to lower 80s and upper 60s-around 70 
for Cape Cod. Very warm temperatures are expected further north and 
west from there, with persistent SW flow keeping the eastern MA sea 
breeze from developing. Of the two days, Wednesday projects as the 
warmest. Highs on Tuesday away from the southern coast should reach 
into the lower to mid 80s, with readings near 80 for the North Shore 
into Greater Boston. Probabilistic maximum temperature data from the 
NBM for Wednesday indicates 50-70% probs for highs reaching the 90-
degree mark in the CT and Merrimack Valleys! Mid to upper 80s 
being common to the Providence-Plymouth corridor. Kept highs for
southeast coastal New England on Wednesday into the 70s to low 
80s. Thus it is looking likely that we'll see summerlike 
temperatures making their first appearance in 2024 on Tuesday 
and Wednesday for a large part of Southern New England, with 
many likely not yet acclimatized to this warmth as yet. It's 
also more of the "toasty" heat versus the oppressive/muggy kind:
very warm ambient air temps but with tolerable humidity levels,
as dewpoints are expected in the mid to upper 50s. 

A cold front then approaches sometime on Thursday, with increasing 
cloud cover. The biggest question mark is on the timing of the 
front, which will influence both how warm we get pre-frontal 
passage and the potential potency of showers and t-storms along 
and ahead of the front. Not out of the question that Thursday 
could still be quite warm if we see a slower timing similar to 
the ECMWF. Kept temps a little cooler than NBM but even with 
clouds we should see highs reach the lower to mid 80s again for 
most except southeast New England. Thursday could also feature 
scattered strong to perhaps severe t-storms too if the timing of
the front coincides with peak daytime heating; GFS shows a 
convective environment with about 1000 J/kg of CAPE with about 
40-45 kt of wind shear in the 0-6 km layer for Thursday. 
Machine-learning progs from Colorado State weren't available 
with the 00z guidance but the prior run hinted at the potential 
for storms becoming severe in interior sections of New England. 
Kept PoP around 30-50 percent, but those will need to be 
adjusted pending the timing of the front. But Thursday should be
the next best chance for rains. 

A more seasonable airmass then returns on NW flow for Friday and 
Saturday, with drier weather also returning.

&&

.AVIATION /11Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

12z TAF Update:

Today: High confidence in trends but lower to moderate on 
visbys and coverage of any showers.

IFR to periods LIFR ceilings from central MA and RI eastward,
with 3-6 SM visby BR and intervals of drizzle or spotty rain 
showers; categorical improvement is not expected. MVFR ceilings
for the western airports should trend to VFR by 17-19z. NE 
winds around 10-12 kt for the coastline, and around 4-7 kt 
across the interior.

Tonight...

Conditions deteriorate overnight with widespread fog, LIFR to
MVFR once again. Pockets of drizzle likely across eastern MA/RI
and the Cape and Islands. NE winds diminish to near calm across
the interior, leading to fog, and 15kt across the outer Cape. 

Monday...

LIFR to MVFR and any fog that develops overnight will quickly
rebound to VFR for the duration of the day, though it may take
until 15Z or so to burn off on the Cape and Islands. Winds
generally less than 10kt and will finally begin to shift from
the E/NE to the S, shifting first across the interior and last
along the eastern coastline. 

KBOS TAF...High confidence in TAF/trends but lower to moderate
on visbys and rain coverage. IFR ceilings today and tonight, 
areas of DZ/BR with visbys around 3-6 SM. Visbys probably trend 
closer to 6SM by late this morning. Sub-VFR likely into at least
a part of Monday morning. NE winds around 10-12 kt today, 
easing to around 4-8 kt tonight and Monday.

KBDL TAF...High confidence in TAF/trends but moderate on timing.
MVFR initially, although cloud bases lift to VFR around/after 
18Z. Sub-VFR returns tonight. NE winds around 4-7 kt today and
tonight becoming more southerly on Monday.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday Night: VFR. 

Wednesday through Wednesday Night: VFR. Breezy. 

Thursday: VFR. Breezy. Chance SHRA, chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

3 AM update...

Sunday... High Confidence. 

Offshore low and maritime high move very little, thus morning
low clouds, fog and spotty light rain and drizzle expected. Some
improvement in the afternoon. NE winds 10 to 20kt. Seas in
excess of 5ft across the outer waters.


Sunday night...High confidence. 

More of the same weather given offshore low and maritime high
persist. Lighter winds and maritime high slowly advects over the
MA/RI waters. Small craft conditions continue for the eastern
outer waters with seas over 5 feet. 

Monday... High confidence

Morning stratus/fog/drizzle will clear gradually though the day,
though may hang tough across the waters through 18Z/20Z. NE
winds gradually shift to the south late in the day, but high
pressure over New England will keep winds rather light, 5-10kt
with an occasional morning gust to 15kt. Small craft conditions
possible for the extreme outer waters with seas still around
5ft. 

Outlook /Monday Night through Thursday/... 

Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. 

Tuesday through Wednesday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ250.
     Small Craft Advisory until 2 PM EDT Monday for ANZ254.

&&

$$

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