Lexington Weather

Lexington, Massachusetts, USA

46°F
3/28/2024 5:43am 
  • Lexington Conditions: Rain, Mist, Overcast
  • Temperature: 46.0°F / 7.8°CWarmer 0.1°F than last hour.
  • Dew Point: 44.4°FIncreased 0.2°Fsince last hour.
  • Relative Humidity: 94
  • Wind: Calm, 10-min avg: Calm, gust: None
  • Barometer: 29.97 in Steady
  • Visibility: 3 miles
  • Rain Today: 0.16 in
  •   

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 231416
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1016 AM EDT Sat Mar 23 2024

.SYNOPSIS...
Active period of weather today through tonight with heavy rain,
flooding, wintry weather, and marine hazards. Drying out Sunday
into early next week but rather windy along the coast, 
especially Cape and Islands. Below normal temperatures will 
prevail. The next chance of rain will be Wednesday and Thursday 
as another frontal system approaches.

&&

.NEAR TERM /THROUGH TONIGHT/...

10 AM update...

Forecast is largely on track. The main change with this update
was to continue to lower the forecast temperatures today by a
few more degrees, especially over southern areas. Observed 
temperatures were 2-3 degrees behind the forecast and the latest
hi-res guidance indicates this trend continues through the day,
only reaching the low 50s in southeast MA. The winter weather
advisory is being extended into the early afternoon for northern
MA to account for lingering near/sub freezing temps. 

Previous Discussion...

Expansive area of cooling cloud tops lifting north along the 
mid Atlc and NE with widespread precip moving across SNE. Snow-
ice line is lifting north across far northern MA and will move
into southern NH/VT during the next 1-2 hours. Icing will be the
main concern this morning across interior MA where temps are in
the upper 20s to lower 30s with low level cold air lingering 
through the morning and possibly into the early afternoon across
the higher elevations in far northern MA.

Strong signal for a period of very heavy rain moving into CT/RI
and portions of central and eastern MA later afternoon through
the evening. Very strong low level convergence develops along 
the surface boundary ahead of low pres, with very favorable
coupled upper jet structure enhancing ascent. Potential for 2+ 
inches of rain in a 3 hour period will likely lead to 
widespread street flooding and some river flooding. 

Previous discussion...

* Heavy rain this afternoon through tonight may poor drainage, 
  urban, small stream flooding... in addition to flooding on the 
  larger rivers. 

* Freezing rain potential for northern Connecticut and central
  and western Massachusetts through late morning.

* Period of gusty winds late Saturday night into Sunday morning for 
  Rhode Island and southeast Massachusetts. 

Surface low pressure system develops to the south, and will quickly 
intensify throughout today, as it phases with northern shortwave. Do 
expect the low pressure system to track from the Jersey coast to the 
Cape Cod Canal this afternoon, before racing into the Gulf of Maine 
this evening. There have been minor changes to the forecast, first 
off 00Z guidance has come in colder, areas outside of Rhode Island 
and southeast Massachusetts could struggle to warm above 40 degrees, 
there will be a fairly sharp cutoff, mid 40s in Boston to mid 50s 
near Taunton. Have lowered temperatures across most of Massachusetts 
(outside of the southeast section) and north/central Connecticut. 
It is here colder temperatures, at or just below freezing will 
linger into the mid morning, thus expecting the threat for freezing 
rain to expand into northeast Connecticut and southern Worcester 
County. Have expanded the Winter Weather Advisory as a result. It is 
worth noting, there could be minor ice accumulation for extreme 
northwest Rhode Island, places like Burrillville where there is some 
higher elevation. The freezing rain threat ends by noontime, the 
only exception would be far northwest Franklin County in 
Massachusetts where spotty freezing rain could linger as late as 
2pm. 

Elsewhere in northern Massachusetts, areas along and north or RT 2 
will have minor snow/sleet accumulations of an inch or two before 
turning over to rain, thus washing it away. 

The heaviest rain still expected to arrive in western Connecticut 
and Massachusetts around noon time, but may take until 4pm to reach 
the I-95 corridor. Some good news, this is a progressive system, 
exiting east of the coastal waters by midnight, with a few lingering 
showers for Cape Cod and the Island through as late as 4am. 

Rainfall amounts have not changed, we still expected widespread 2-3 
inches, though the axis of the heaviest rain has shifted to the 
west, with a maxima from Connecticut into Rhode Island. High-res 
guidance support locally higher amounts as well. HREF QPF ensemble 
probability-matched mean has a reasonable worst case scenario of 
isolated amounts greater than 4 inches for central Connecticut! HREF 
also highlights central Connecticut with the potential, an 80 
percent chance, that one inch of rain could fall in as little as 
three hour period. The potential is there for poor drainage, urban, 
and small stream flooding in addition to flooding along the main 
rivers. The Flood Watch remains in effect through early Sunday 
morning. Areas that typically experience nuisance flooding will want 
to take note and prepare accordingly.

A few of the area rivers we are going to need to monitor include the 
Pawtuxet River at Cranston, where minor flooding is likely, greater 
than an 80 percent chance, and 40 percent chance of moderate 
flooding. The Wood River at Hope Valley, where minor flooding is 
likely, greater than 95 percent, and a 35 percent chance of moderate 
flooding. Both of these rivers could reach flood stage late tonight. 
The larger river in Connecticut are forecast to remain below flood 
stage, but we will have to keep an eye on the smaller streams, 
especially those in Hartford County where there is a signal for a 
localized 4"+ of rain. Eastern Massachusetts, the Taunton River at 
Bridgewater has a greater than 65 percent chance of reaching minor 
flood by early Monday morning, as this river is slow to respond from 
the runoff. 

Later this afternoon a strong low level jet develops as the surface 
low passes over the waters south of Rhode Island, between 20z and 
04z, the 925mb jet is 70-80 knots, with some guidance as strong as 
85+ knots. Have opted to issue a Wind Advisory for areas of Rhode 
Island, southeast Massachusetts and the islands. Timing, the core 
winds are expected between 5pm and 11pm. This is where we have the 
greatest chance of southerly winds gusts of 45 to 50 mph. 

These strong winds also coincide with high tide for Narragansett
Bay, see the Tides/Coastal Flood section at the end of the AFD
for more information. 

As the system exits the region late tonight there will be clearing 
from west to east and wind shift to the north/northwest and remain 
gusty between 30 and 40 mph. Temperatures fall into the 20s and low 
30s.

&&

.SHORT TERM /SUNDAY/...
Sunday is much drier, with the surface low pressure system off shore 
our region placed in a tight pressure gradient. Clouds linger over 
the eastern waters, and Cape Cod, further west we trend towards more 
in the way of sunshine. Afternoon highs are cooler than normal, in 
the mid 30s to 40 degrees. Though it will feel much colder due to 
the persistent north/northeast winds gusting between 25 and 35 mph. 
The feel like temperature will be mostly in the 20s for Sunday 
afternoon.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Highlights: 

* Mostly dry with below normal temps Mon and Tue, but risk for some 
  spotty light rain Cape/Islands and possibly eastern MA, 
  especially Tue. Windy near the coast.

* Unsettled Wed into Fri. Low pressure may bring more rain sometime 
  Thu into Fri

Monday and Tuesday...

Cutoff low will maintain a surface low pres well to the south 
through Tue as high pres builds over the Maritimes. This will set up 
a strong NE pressure gradient bringing windy conditions along the 
coast Monday, especially Cape/Islands where some 40-50 mph gusts 
possible. Winds should diminish somewhat by Tue as the low level 
wind field weakens. Mainly dry conditions expected with below normal 
temps, but area of deeper moisture rotating in from the east could 
bring spotty light rain to Cape/Islands and possibly portions of 
eastern MA Mon and especially Tue. There remains some uncertainty 
with how far west this moisture gets so our PoPs are low, but better 
chance for some wet weather will be on Tue. ECMWF and GGEM are most 
aggressive with rain spreading west across much of SNE Tue. May need 
to raise PoPs for Tue if this trend continues. Expect at least more 
cloud cover across eastern New Eng Mon and Tue. Highs will range 
from the lower 40s eastern MA to upper 40s CT valley. 

Wednesday through Friday...

Longwave trough moves slowly east from the central CONUS with 
shortwave energy and deeper moisture approaching from the west 
possibly bringing showers Wed. Then a potentially potent southern 
stream system will be developing and lifting NE from the SE CONUS. 
Forecast confidence is low on how this system evolves and its 
subsequent track but potential for another coastal low pres to bring 
more rain sometime Thu into Fri. Details are uncertain.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Today...High confidence in trends. Moderate in timing.

FZRA may persist at BAF/ORH through as late as 15Z, but will 
changeover to rain thereafter with surface temps rising above 
freezing after sunrise. MVFR cigs/vsbys deteriorate to IFR
through the morning from W to E. Rain picks up in intensity 
after 20Z across CT then heavy rain spreads NE into RI and
portions of central and eastern MA this evening.  Southeast 
winds gradually increase throughout the day ranging from 10 kt 
across the interior to 15 to 20 kt over the coastal plain. A 
strong low level jet will likely increase winds across Rhode 
Island and southeast MA between 21z and 03z, gusting as high as 
35 to 40 knots. 

Tonight...High confidence in trends. Moderate in timing. 

IFR/MVFR cigs improve to VFR returns as precip gradually ends  
from west to east from 03Z to 09Z. Rain lingers a bit longer 
over The Cape/Island terminals likely tapering off between 06 
and 10Z with VFR returning to this area between 09 and 12Z. 
Winds strengthen after 00Z behind a surface cold front. 15 to 25
knot sustained northwest winds with gusts up to 35 knots. 

Sunday...High confidence. 

VFR. Strong winds with local gusts up to 40 kt.

KBOS TAF...Moderate confidence in TAF. MVFR with -RASN possible
through 10Z/11Z, followed by RA, becoming heavy this afternoon
with IFR conditions. Rain ends late this evening around 04z. 
Gusty southeast winds as well, nearing 30 knot gusts around 00z
through 02Z/03Z. Shift from southeast wind to northerly wind by
03z tomorrow with improving CIGS to MVFR.

KBDL TAF...Moderate confidence in TAF. MVFR with -FZRA possible
through 10z, then rain for the rest of today with IFR to LIFR
conditions. Rain becomes heavy this afternoon and through this 
evening, ending after 00z. Light northeast wind will become 
northerly after 00Z and gusting 20 to 25 knots, and improving
CIGS to MVFR.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday Night: VFR. Strong winds with local
gusts up to 40 kt. 

Tuesday: Mainly VFR, with areas MVFR possible. Windy with gusts
up to 35 kt. 

Tuesday Night: MVFR/IFR conditions possible. Windy with areas
of gusts up to 30 kt. Chance RA.

Wednesday: Mainly VFR, with local IFR possible. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

* Gale Warning in effect for all waters Saturday and continues
  into Sunday.
  

Today: Conditions deteriorate rapidly tomorrow as a strong low 
pressure moves over southern New England. Steady 20 knot 
southeast winds persist with gusts up to 40 knots possible, 
especially over the southern coastal waters. Seas gradually 
increase from 4 feet early in the day to 6 to 9 feet by evening.
Nearshore eastern zones stay a bit lower with 4 to 6 foot seas.

Tonight: A cold front moves over the waters tomorrow night. 
Winds become even stronger out of the north/northwest with 30 
knot sustained winds for most of the marine zones. Wind gusts 
from 30 to 40 knots. Seas increase to 10 to 13 feet over the 
outer coastal waters, and 6 to 10 feet for the nearshore waters.

Sunday: Low pressure system to our north will continue northerly
gales with gusts to 40 knots. Seas on the outer waters are
greater than 12 feet, near shore waves are 6 to 10 feet. 

Outlook /Sunday Night through Wednesday/...

Sunday Night: Moderate risk for gale force winds with gusts up
to 45 kt. Rough seas up to 14 ft. 

Monday through Monday Night: Moderate risk for gale force winds
with gusts up to 45 kt. Rough seas up to 14 ft. Slight chance
of rain. 

Tuesday: Low risk for gale force winds with gusts up to 40 kt.
Rough seas up to 13 ft. Slight chance of rain. 

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft. Slight chance of
rain. 

Wednesday: Winds less than 25 kt. Areas of rough seas. Chance
of rain.


&&

.TIDES/COASTAL FLOODING...
There is some concern for Narragansett Bay during the high tide this 
evening. Strengthening low level jet will be lifting north along the 
coast near the time of high tide but it is possible the core of the 
jet stays just to the east. If it does remain to the east, surge 
will likely be limited to 1.5-2 ft which will keep water levels 
below flood. However, there is some risk for a 2.5 to 3 ft surge if 
the low level jet axis and stronger winds impact RI. This would 
bring Providence and Fall River (Mount Hope Bay) into minor flood. 
Confidence is not high enough to issue an advisory so we will go 
with a coastal flood statement. The worst case scenario is for 
pockets of minor flooding.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory until noon EDT today for CTZ002>004.
     Flood Watch through Sunday morning for CTZ002>004.
MA...Winter Weather Advisory until noon EDT today for MAZ002>004-
     008>012-026.
     Flood Watch through Sunday morning for MAZ005>007-009-011>024.
     Wind Advisory from 5 PM this afternoon to 11 PM EDT this 
     evening for MAZ017>024.
RI...Flood Watch through Sunday morning for RIZ001>008.
     Wind Advisory from 5 PM this afternoon to 11 PM EDT this 
     evening for RIZ004>008.
MARINE...Gale Warning from 2 PM this afternoon to 2 PM EDT Sunday for 
     ANZ230>235-237-251.
     Gale Warning from 2 PM this afternoon to 2 AM EDT Sunday for 
     ANZ236.
     Gale Warning from 2 PM this afternoon to 8 PM EDT Sunday for 
     ANZ250-254>256.

&&

$$

SYNOPSIS...KJC/Dooley
NEAR TERM...BW/Dooley
SHORT TERM...Dooley
LONG TERM...KJC
AVIATION...KJC/Dooley
MARINE...KJC/Dooley
HYDROLOGY...
TIDES/COASTAL FLOODING...KJC
      

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