Lexington Weather

Lexington, Massachusetts, USA

67°F

5/20/2024 2:30pm

Lexington Conditions: Few Clouds
Temperature: 66.7°F / 19.3°C
Dew Point: 57.7°F
Relative Humidity: 73%
Wind: SSW Calm, 10-min avg: 1 mph, gust: 9 mph
Barometer: 29.99 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 192346
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
746 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 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/...
No big changes here, a warming trend continues Tuesday and Wednesday 
with the chance for this summer-like warmth to continue on Thursday. 
A cold front moves across the region on Thursday, perhaps bringing a 
few stronger storms. Mixed signal heading into next weekend as the 
deterministic guidance remains split over a dry or semi-wet weekend. 

An anomolously warm air mass, driven by a modest mid-level ridge, is 
expected to linger over much of New England into Thursday, leading 
to well above normal surface temperatures. Global guidance 
suggests 850mb temperatures are +6C to +11C above what is normal
over the course of those three days. The ridge does break down 
late Thursday into Friday a mid-level trough swings through. 

Tuesday afternoon there are high probabilities, greater than 
80% for temperatures AOA 85 degrees, locations like Hartford, 
Springfield, Worcester, and Lowell. Many spots across the 
interior top out between 85F-89F, while closer to the coast a 
southwest wind keeps locations south of 
Providence/Taunton/Plymouth in the 70s, though the immediate 
coastline in the upper 60s. Wednesday looks to be the warmest 
day with a large portion of northern Connecticut, northern Rhode
Island, and much of Massachusetts (outside of southeast MA) 
with greater than 80% probabilities of afternoon temperatures 
AOA 85 degrees. It is not out of the question we have a few 
spots pushing 90 degrees, places in the Merrimack and CT River 
Valley have a greater than 70% chance. While less likely, there 
are even low probabilities of temperatures at or above 95F, 
around 40% in the Merrimack Valley. Thursday, the maximum 
temperatures will really depend on what time a cold front moves 
through and how much cold cover develops. Given the 
uncertainties, continues with NBM guidance, highs likely reach 
back into the middle 80s away from the coast. Temperatures 
turning more seasonable with highs in the 70 for Friday into 
next weekend. 

Much of this week is dry, the mid-level ridge does support a drier 
pattern. Not out of the question there could be a rouge afternoon 
shower/thunderstorm mainly areas northwest Massachusetts, but 
the better chance for showers is Thursday. Guidance is in pretty
fair agreement a cold front moves across the region with the 
potential for thunderstorms - whether or not they are severe is 
still to be seen, but there are signs that the atmosphere could 
be favorable with modest CAPE, 1500 J/kg and effective shear of 
40 kts. Based off the previous deterministic run, the CSU 
machine learning have 5% to 15% of severe weather, something to 
monitor as we head into this week. Drying out on Friday, but 
there remains uncertainty with this upcoming weekend whether or 
not we see rain or not.

&&

.AVIATION /23Z SUNDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

00z TAF Update:

Tonight...Moderate confidence in CIGS, low confidence in VSBY.

Rather complex forecast overnight, in general ceilings fall to
IFR with isolated areas of LIFR. Where confidence is lower are
areas in northern Connecticut and western Massachusetts where
drier air is eroding cloud cover. Though, the thought is the 
clouds across Rhode Island and eastern Massachusetts expand 
westward. Area of fog and drizzle pushed into eastern MA with 
visibilities 1-3SM, high-res guidance suggests this may lower to
less than 1SM before briefly improving between 02z-05z to 
2-4SM. After 05z/06z visibilities remain down 1SM or less for 
the rest of the overnight hours. Northeast winds 10 to 15 knots 
ease overnight, becoming light and less than 5 knots. 

Monday...Moderate confidence.

IFR/LIFR cigs with patchy fog early, will slowly improve to VFR
all terminals, but 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...Moderate confidence. 

VFR but MVFR vsbys developing in patchy fog. 

KBOS TAF...Moderate confidence in TAF trends but lower
confidence in visibilities. IFR/LIFR cigs with IFR to MVFR vsby
into Monday morning, 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...Dooley
AVIATION...Nocera/Dooley
MARINE...Nocera/Dooley