Lexington Weather

Lexington, Massachusetts, USA

64°F

5/20/2024 5:59pm

Lexington Conditions: Clear
Temperature: 63.9°F / 17.7°C
Dew Point: 56.8°F
Relative Humidity: 78%
Wind: Calm, 10-min avg: Calm, gust: 1 mph
Barometer: 29.96 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 191904
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
304 PM EDT Sun May 19 2024

.SYNOPSIS...
The coastal storm that has brought low clouds, drizzle and cool 
northeast winds to RI and eastern MA, finally begins to exit out to 
sea tonight.  This gives way to a significant pattern shift to drier 
and warmer weather beginning 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, hence, a somewhat dry heat. 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 AM MONDAY MORNING/...

3 PM Update:

Low level moist onshore jet continues to deliver overcast
conditions and some spotty drizzle across RI and eastern MA, 
including Cape Cod and the Islands. Meanwhile, breaks in the 
overcast are occurring across CT into MA, eastward into the 
Worcester Hills. Temps are responding to the strong May 
sunshine, with temps warming through the 60s there and a few low
70s, including 71 at BDL currently. Meanwhile, short wave 
energy traversing southward from the ME coast will continue to
delay height rises from advancing eastward today. This also
results in a nearly stationary low level ENE jet into eastern MA
and RI, with the low level jet slowly shifting southward 
overnight, along with ridge of high pressure advecting south 
into SNE. 

Thus, drier trends overnight. However, low level moisture will 
likely remained trapped beneath the subsidence inversion from 
the surface ridge building southward. Hence, low clouds will 
remain stubborn across RI and eastern MA tonight and likely  
drifting back into CT and western/central MA, along with patchy
fog possible. This low level moisture will yield seasonably 
cool temps overnight, with lows in the upper 40s and lower 50s. 
Although, it will feel cooler with northeast winds 15-25 mph, 
highest over southeast MA and RI, slowly slackening tonight as 
the surface ridge builds southward. 

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...

3 PM update...

* Big improvement, more sunshine & warmer temperatures
* Low 80s possible CT River Valley, including Hartford/Springfield

Monday...

Once short wave energy exits the eastern MA coast tonight, this 
allows height rises to advect Monday across the region from west to 
east and more importantly, low level jet easing and moving offshore. 
This ridging and associated subsidence will allow strong May 
sunshine to erode low level moisture/clouds and possible patchy fog 
Monday morning and give way to at least partial afternoon sunshine 
to the entire region. 12z models have trended warmer and this seems 
reasonable given the height rises and morning clouds giving way to at 
least partial late May sunshine. 850 mb temps increase to about +12C 
and 925 mb temps warm to +18C to +20C western MA, to +13C across 
southeast MA. This will support highs in the low 80s across western 
MA/CT, with much of the region seeing highs in the 70s and as far 
southeast into the I-95 corridor of MA/RI. With surface ridge over 
the area, afternoon seabreezes will develop and cap highs in the 60s 
for the coastline, possibly only into the upper 50s for the outer 
Cape and Nantucket. 

Monday night...

Deep layer ridge over SNE will provide dry weather. Light winds and 
dew pts slightly above normal (low 50s), may yield patchy fog. This 
will also result in mild overnight temps, with lows 50-55. 

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...

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 /19Z SUNDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

18z TAF Update:

Through 00z...

Improving cigs to MVFR continue to spread from west to east across 
CT and MA into the Worcester Hills, RI and even into parts of 
southeast MA. Some uncertainty how much farther eastward this 
progresses before sunset. Radar still picking up some spotty drizzle 
across southeast MA into RI. This should slowly shift south through 
00z. NE winds 10-15 kt with gusts up to 25 kt across Cape Cod and 
the islands. 

After 00z...

Decreasing trends with IFR (possibly LIFR) cigs and MVFR vsbys in fog 
drifting and developing westward from the coastline into the 
interior overnight. Any areas of drizzle during the evening should 
come to an end after midnight. NE winds 10-15 kt with gusts up to 20 
kt in the evening across southeast MA, will slacken overnight. 

Monday...

IFR/LIFR cigs with mainly MVFR vsbys in fog early, will slowly 
improve to VFR all terminals, but obviously delayed until the 
afternoon or late in the day across Cape Cod and the Islands. Light 
NE winds become east and then southeast late in the day. 

Monday night...

VFR but MVFR vsbys developing in patchy fog. 

KBOS TAF...High confidence in TAF trends but lower on exact timing. 
MVFR cigs and VFR vsbys this evening, then lowering to IFR/LIFR cigs 
with MVFR vsby overnight into Monday morning. Then eventually 
improving to VFR by Monday afternoon. NE winds tonight, becoming 
east Monday and then southeast late in the day. 

KBDL TAF...High confidence in TAF trends but lower on exact timing. 
VFR continues into early evening, then some uncertainty how low cigs 
and vsbys overnight into Monday morning, as low clouds and patchy 
fog develop overnight. High confidence in improving conditions 
Monday to VFR by midday or so.  

Outlook /Tuesday through Friday/...

Tuesday 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 PM update...

Tonight...high confidence. 

Offshore low continues to generate marginal SCA with NE winds up to 
25 kt (in gusts, not sustained) and seas up to 6 ft across the 
eastern MA waters, slowly subside tonight. Vsby may be reduced to 1-
3 miles at times in drizzle and fog. 

Monday... High confidence

Lows clouds/drizzle and patchy early morning fog with vsbys 1-3 
miles, slowly burns off with improving conditions mid to late 
afternoon. High pressure over SNE results in light NE winds become 
east and then southeast late in the day. 

Monday night...high confidence. 

Ridge of high pressure crest over the waters, yielding light SE 
winds becoming SW. Patchy fog may limit vsby at times. 

Outlook /Tuesday through Friday/... 

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...Nocera/Dooley
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...Loconto
AVIATION...Loconto/Nocera
MARINE...Loconto/Nocera