Lexington Weather

Lexington, Massachusetts, USA

66°F

5/20/2024 3:00pm

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 172330
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
730 PM EDT Fri May 17 2024

.SYNOPSIS...
Increasing clouds with onshore winds and spotty light 
rain/drizzle for much of southern New England tonight. Cool and 
cloudy with light rain/drizzle for much of the region on 
Saturday. We are then looking at a prolonged spell of dry 
weather with warming temperatures starting Sunday and continuing
through Wednesday. High temperatures could approach the mid 80s
by Tuesday and/or Wednesday in interior Southern New England, 
with temperatures in the 70s near the coasts. Our next chance 
for rains doesn't appear until around Thursday.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Highlights

* Increasing clouds with spotty light rain/drizzle spreading in
  from SE to NW. Best shots across central MA/RI eastward.

Ridge axis in place offshore of the Mid Atlantic this evening
with a cutoff just south of Nova Scotia and a shortwave over the
eastern Great Lakes. The ridge gets flatten out as the shortwave
lifts into Upstate New York late tonight. The cutoff becomes an
open wave as it lifts to the southeast of Nova Scotia. A broad
low will continue to rotate well to the SE of the Cape/Islands,
but will meander northwestward this evening. Portions of our
interior will have a weak high nudging in.

Main concern in the near term is the increasing cloud cover
along with spotty drizzle/light rain spreading in from SE to NW
tonight. Will see our PWATs surging across central MA/RI into
eastern MA to 1-1.25 inches with E/SE flow aloft. This in
combination with the increasing low level moisture and the broad
low meandering toward us could squeeze out some light
rain/drizzle. Guidance tends to struggle in more weakly forced
situations like this, but there is a pretty good consensus for
light precip across eastern MA, but more uncertainty as you
spread inland. Have kept chances of precip along the immediate
coast and lower shots further inland. Given the weak forcing
am not anticipating much other than perhaps a few hundredths of
QPF. 

Overnight low temperatures are roughly around seasonable levels,
which is right around 50 degrees.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Highlights

* Dreary Saturday with spotty light rain/drizzle and
  unseasonably cool.

* Still unsettled with spotty light rain/drizzle Saturday night. 

Shortwave trough will be working its way through New England
Sat. Think it cuts off just east of our region heading into Sun,
which will keep us unsettled. Broad area of low pressure remains
southeast of our region Sat and Sat night. Portions of the
interior may see a weak high nudging in.

As previous shift mentioned a tricky forecast for Sat. Though am
leaning toward the latest ECMWF and solutions similar to it. The
reason being is in these blocked flow type patterns the ECMWF
tends to break things up much slower than other guidance
sources, which tends to be closer to reality. Based on this am
anticipating a cloudy and dreary Sat for southern New England. 
Will have persistent NE to NNE winds through this period. Should
see an abundance of low level moisture per RH values in the 
1000-850 hPa layer per all guidance. Some hints that there could
be some breaks in the clouds due to the weak high nudging in 
for portions of the interior, but not super optimistic about it 
given the low level RH fields.

Should see isolated to scattered light rain/drizzle across much
of southern New England on Sat. Will have PWAT values of roughly
1-1.5 inches. This plume may slide further offshore Sat night,
which could potentially bring a break in activity for portions
of the interior. Have kept fairly widespread slight chance to
chances of precip with the best shots across eastern areas.
Again though have leaned fairly heavily on the ECMWF, which is
much slower to improve conditions. We will also have a
northeasterly oriented 20-30 kt LLJ which given the weak forcing
should be enough for some light rain/drizzle. Given the
cloudier forecast did significantly lower our highs on Sat.
Think for most will be unseasonably cool with widespread 50
degree highs. Think the best shot for low/mid 60s is across the
CT River Valley. Will be quite similar temp wise Sat Night as
tonight with lows around 50.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key messages...

* Dry weather is expected through at least the middle of next week.

* After a slightly cooler than average weekend a big warm-up arrives 
  for early next week with 80s possible by Tuesday and Wednesday, 
  potentially into Thursday. 

Details...

Sunday...

The trend is our friend as we go into the second half of the 
weekend, with high pressure nudging closer bringing less cloudiness 
and warming temperatures compared to Saturday. Northeast flow off 
the ocean will continue to keep temperatures cooler along the east 
coast (upper 50s) but typical locations further west like the CT 
Valley will reach the low 70s. 

Monday through Wednesday...

The first three to four days of next week will offer a stretch of 
summer-like weather the likes of which we haven't seen much of so 
far this year. At the surface high pressure continues to move 
overhead, eventually turning winds out of the SW by Tuesday. So, 
while increasing sun/insolation on MOnday along with a warming 
airmass will lead to warmer temps, in the mid to upper 70s, the heat 
arrives in earnest for Tuesday and Wednesday. This is when SW flow 
and 850 mb temps jumping from +10C on Monday to +15C on Tuesday will 
lead to widespread temperatures in the low to mid 80s. The coolest 
spots will be areas along and adjacent to the south coast, 
especially Cape Cod where temps remain in the low to mid 60s. 

Late week...

The warm and dry pattern may break down by Thursday as a mid level 
shortwave and surface cold front approach bringing the return of 
rain chances to the forecast, but timing and other details remain 
uncertain.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Tonight... Moderate confidence

VFR to start away from the Cape/Islands where MVFR/IFR
conditions persist. Will see this MVFR/IFR stratus spread
northwestward as the night progresses. Though think IFR with
localized LIFR remains generally ORH-BVY-WST eastward. Will have
spotty rain/drizzle with this stratus. Persistent NE flow at
5-15 kts. Could see some gusts of 20-25 kts across the
Cape/Islands.

Saturday...Moderate confidence.

MVFR to IFR conditions persisting with localized LIFR across the
Cape/Islands. Think that the CT River Valley could break out to
VFR toward 18Z. Will have persistent NE winds at 5-15 kts with a
few gusts up to 20 kts along the immediate east coast. Spotty
rain/drizzle throughout the day.

Saturday Night...Moderate confidence.

MVFR to IFR conditions persist due to pesky onshore flow. Could
also have some spotty localized LIFR condition. Light rain and
drizzle continues with the best shot along the immediate
coastline. Winds NNE to NE at 5-15 kts with a few gusts up to 20
kts toward daybreak along the Cape/Islands.

KBOS TAF...High confidence in TAF through 00Z. Moderate after
this time.

VFR with NE winds at 10-15 kts through roughly 02Z. Will see
ceilings lowering to MVFR/IFR tonight with drizzle/rain
spreading in toward 03-06Z. Light rain/drizzle persistent
through Sat with NE winds and IFR conditions. 

KBDL TAF...High confidence in TAF. 

VFR this afternoon and this evening. Could see some borderline
MVFR ceilings spread in late tonight, but better shot comes Sat
AM and persists through the afternoon. Could see some spotty
rain/drizzle on Sat.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local IFR possible. Breezy. 

Sunday Night through Monday: Mainly VFR, with local MVFR
possible. 

Monday Night through Tuesday Night: VFR. 

Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Extended the SCA for the eastern outer waters through 12Z Sun
for elevated seas.

Tonight...High confidence.

Winds remain out of the NE at 10-20 kts with some 20-25 kt gusts
this evening. Stratus/fog along with light rain/drizzle across 
the waters. Visibilities of 1/2 to 4 SM with the lowest near and
southeast of Nantucket. Seas 1-3 ft across the inner waters and
4-7 ft for the outer.

Saturday... High confidence.

Scattered light rain and drizzle across the waters. Will have
visibilities of 3-5 SM. Persistent 15-20 kts out of the NE with
gusts up to 20 kts. Seas 1-4 ft across the interior waters and
4-6 ft for the outer.

Saturday Night...Moderate confidence.

Scattered light rain and drizzle anticipated to persist. Though
some uncertainty on this. Will continue to see NE winds at 10-15
kts and gusts around 20 kts. Visibilities of 3-5 SM and seas 3-6
ft for the outer waters.

Outlook /Sunday through Wednesday/...

Sunday through Sunday Night: Winds less than 25 kt. Seas up to
5 ft. 

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

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

Tuesday Night through Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Sunday for ANZ250-254.
     Small Craft Advisory until 8 PM EDT Saturday for ANZ255-256.

&&

$$

SYNOPSIS...BW/BL
NEAR TERM...BL
SHORT TERM...BL
LONG TERM...BW
AVIATION...BW/BL
MARINE...BW/BL