Old Res Weather

Lexington, Massachusetts, USA

39°F
3/29/2024 6:42am 
  • Lexington Conditions: Light rain, Overcast
  • Temperature: 38.7°F / 3.7°CColder 0.5°F than last hour.
  • Dew Point: 36.9°FDecreased 0.7°Fsince last hour.
  • Relative Humidity: 93%Decreased 1.0% since last hour.
  • Wind: Calm, 10-min avg: Calm, gust: None
  • Barometer: 29.65 in Steady
  • Visibility: 10 miles
  • Rain Today: 0.37 in
  • UV Index: $VPuv None
  •   

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 230529
AFDBOX

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

.SYNOPSIS...
Active period of weather arrives late tonight through Saturday 
night 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 /UNTIL 6 AM THIS MORNING/...
Update: 10:25pm 

No changes to the forecast at this point in time, have blended
in latest high-res guidance to better track the increasing
dewpoint temperature. Did toss in a mention of flurries, mainly
across central and western MA over the next two hours as a warm
front begins to lift north. Still, there is a good deal of dry
air at the lowest level of the boundary layer. As this saturates
we will start to see more of the precip reach the ground. 

Did get a report of a snow flakes flying in central Worcester
County over the past hour. It is difficult to see on area web
cameras, but mPING reports are slowly coming in to support this.
As of 10:15pm there remains a large T/Td depression, but it is
worth nothing the dewpoint has climbed from -1F to +12F in the
last 75 minutes. 

One note about the incoming rain. It is worth nothing the 00z
HRRR has shifted the axis of the heaviest rainfall to the west,
more inline with central and eastern CT. The 00z NAM 3KM does
show a slight shift west as well, but not to the extreme of the
HRRR. Will be evaluating the rainfall potential over the next
couple hours. Nevertheless, southern New England should expect 
widespread 2-3 inches of rain between late tonight through early
Sunday morning. The part of the forecast with lower confidence 
is the exact area the axis of the heaviest rain sets up. We will
continue to monitor this with the rest of the 00z suite of 
guidance. 

Previous Discussion...

Tonight/early tomorrow

First half of the night is quiet across the region with some  
increasing cloud cover and light winds ahead of a robust low 
pressure system that will move over the region tomorrow. Active 
weather begins to settle over southern New England during the 
early morning hours as a surface warm front associated with a 
deepening low-pressure system begins to lift over the region. 
Temperatures on the north side of the warm frontal boundary will
be well below freezing. As warmer air aloft overruns the cooler
air in place, we'll begin to see precipitation develop in the 
form of light snow showers across western MA and CT. As the warm
nose edges further north, a melting layer develops between 
about 850 and 900 hPa. With surface temps remaining at or below 
freezing, this will support a freezing rain profile for 
north/northwest Hartford county, western MA, and northern 
Worcester county. Based on latest suite of ensemble guidance, 
freezing rain may begin as early as 5am across western MA/CT and
continue through 09 to 10 am when surface temps will begin to 
rise above freezing and allow a changeover to rain. Prior to the
changeover, substantial ice accumulations from a few hundredths
of an inch to a tenth of an inch or more will be possible. For 
this reason, a winter weather advisory remains in effect for the
aforementioned areas expected to experience freezing rain. 
Winds increasing out of the southeast to 10 to 15 knots during 
this period as well.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
Tomorrow

By mid-morning tomorrow, surface temps will have increased to
above freezing across southern New England. This will result in 
any remaining frozen precipitation changing over to rain. From 
there on out, the rest of tomorrow is a complete wash out. A 
coastal low develops and moves off the mid-Atlantic coast before
tracking over or just southeast of The Cape/Islands. An
impressive region of frontogenesis develops across southern New 
England by early afternoon and will support a period of heavy 
rainfall that may result in urban, small stream, or poor
drainage flooding. Latest HREF run paints a swath of 2 to 4
inches of rain across CT, RI, and southeastern MA with the
heaviest rainfall between roughly 2pm and 8pm. While confidence 
in a significant rainfall event is higher than normal, even 
subtle changes in the storm track could result in the axis of 
heaviest rainfall lifting north or south, so there still remains
a bit of uncertainty at 24 hours out. Given the relatively wide
goal post for the axis of heaviest rainfall, a flood watch is 
in effect for the southern and eastern forecast areas. Only 
northern Worcester county, Franklin, and Hampshire counties are 
excluded. In addition to small stream flooding, some larger area
rivers in southern RI are at risk for flooding as well (see 
Hydro section). Temperatures range from upper 30s to low 40s 
across the interior/northwest areas tomorrow, with more mild 
temperatures in the upper 40s to low 50s across southeastern MA 
and RI. 

Tomorrow Night

Surface cold front associated with the low-pressure system
moving over southern New England pushes through the region
tomorrow evening. This brings precipitation to and end for most 
of the region from west to east between about 8pm and 2am. 
Clearing and strong northwest winds from 15 to 25 mph will
follow the cold front. Precip lasts a bit longer over The
Cape/Islands tapering off between roughly midnight and 4am. 
Temps dive into the lower to mid 20s across the
interior/northwest areas and upper 20s to lower 30s across 
southeastern MA/RI prior to sunrise on Sunday.

&&

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

* Mostly dry Sun into Tue, but blustery with below normal 
  temperatures. Quite windy over the Cape/Islands

* Increasing risk of wet weather Wed into next Fri. Temperatures  
  trending back above normal late next week.

A broad mid level trough is expected to morph into a mid level  
cutoff over the North Atlantic early next week. This should trap
the surface low pressure beneath it, and keep it lingering
offshore of southern New England. Still some uncertainty in just 
how far offshore this low pressure will wind up being. At
present, thinking the latest NationalBlend (NBM) deterministic
solution is on the pessimistic side of the envelope. Maintained 
a faster departure of clouds and rainfall Sunday.

High pressure over eastern Canada is expected to nudge into our  
region for Monday and Tuesday, leading to mainly dry and partly 
cloudy conditions across most of our region. The exception to 
that will be across far eastern MA, and especially the Cape and 
islands. Thinking clouds may linger longer there, along with a 
few showers Sunday morning. Will possibly need a Wind Advisory 
at some point Sunday into Sunday night into Monday. It's
marginal still, so not very high confidence. With all the other 
ongoing headlines, will wait until confidence increases before 
issuing such a headline.

The weak high pressure should maintain dry weather MOnday and  
Tuesday, but also bring in colder air with a persistent N to NE  
wind. Eventually though, this high pressure should break down
and move farther offshore. That will open the door for a slow-
moving front to impact southern New England late next week, most 
likely some time from late Wednesday into Friday. It should not
be a total washout, but looking at the prospect of a prolonged
period of unsettled weather. Will need to monitor the impact of 
any additional rainfall on our creeks, streams and rivers, which
should still be recovering from the rainfall this weekend.

Temperatures should trend warmer mid week, and likely return to 
above normal temperatures Thursday into Friday.

&&

.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Through 12z...High confidence in trends. Moderate in timing.

VFR/MVFR with light and variable wind, though becoming
southeasterly. Conditions are begin to deteriorate with the 
precip associated with a surface warm front lifting over 
southern New England begins to support MVFR ceilings and light 
precip. 

Frozen precip will be an issue at the western terminals 
(BDL/BAF/ORH). A brief period of -SN, followed by -FZRA, will be
possible beginning as early as 09Z. Elsewhere, any precip will 
be limited to -RA, but likely will be closer to or after 12Z 
before precip reaches the eastern terminals.

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

Light FZRA may persist at BDL/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
by between 16Z and 18Z as rain overspreads the region. Rain 
picks up in intensity after 18Z and remains steady through 00Z. 
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.

Outlook /Sunday Night through Wednesday/...

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

Monday Night: Mainly VFR, with local MVFR possible. Strong
winds with areas of gusts up to 45 kt. 

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

Tuesday Night: Mainly VFR, with areas IFR possible. Windy with
local gusts up to 30 kt. Chance SHRA.

Wednesday: MVFR/IFR conditions possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight

Quiet marine conditions through about midnight tonight.
Thereafter, winds begin to increase out of the southeast ahead
of robust low pressure system with sustained winds of 20 knots
and gusts up to 25 knots by sunrise.

Tomorrow

Conditions deteriorate rapidly tomorrow as a strong low pressure
moves over southern New England. Steady 20 knot southeast winds
persist with gusts up to 35 knots possible, especially over the 
southern coastal waters. Seas gradually increase from 4 feet
early in the day to 6 to 9 feet by tomorrow evening. Nearshore
eastern zones stay a bit lower with 4 to 6 foot seas. A Gale 
Watch is in effect through Monday morning.

Tomorrow Night

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. 

Outlook /Sunday Night through Wednesday/...

Sunday: Moderate risk for gale force winds with local gusts up
to 45 kt. Rough seas up to 15 ft. 

Sunday Night through Monday: gale force winds with gusts up to
45 kt. Rough seas up to 15 ft. Slight chance of rain showers. 

Monday Night: Moderate risk for gale force winds with gusts up
to 45 kt. Rough seas up to 15 ft. 

Tuesday: Low risk for gale force winds with gusts up to 35 kt.
Rough seas up to 13 ft. 

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance
of rain showers. 

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

&&

.HYDROLOGY...
Heavy rainfall tomorrow afternoon and tomorrow evening is likely 
to lead to minor, and perhaps moderate, river flooding across 
southern Rhode Island. Greatest risk for minor flooding appears 
to be along the Wood River at Hope Valley, where the MMEFS 
indicates a 94 percent chance of minor flood stage being
reached, and a 54 percent chance of moderate flood stage being
reached.

Several other rivers across southern New England including the 
Shawsheen, Charles, Assabet, Pawcatuck, and Pawtuxet Rivers are
at an elevated risk to reach at least minor flood stage due to 
excessive rainfall.

The Pawtuxet River at Cranston is of particular concern given
latest ensemble forecast guidance paints a bullseye of 2 to 4
inches of rain over this basin in only a 3 to 6 hour time
period. MMEFS indicates a 63 percent chance of moderate flood
stage being reached, and even a 24 percent chance of major flood 
stage being reached. Residents and businesses near this location
will want to keep a close eye on updates for potential River 
Flood Warnings and take action accordingly. 

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 2 AM to noon EDT Saturday for 
     CTZ002.
     Flood Watch from Saturday morning through Sunday morning for 
     CTZ002>004.
MA...Winter Weather Advisory from 2 AM to noon EDT Saturday for 
     MAZ002>004-008>011-026.
     Flood Watch from Saturday morning through Sunday morning for 
     MAZ005>007-009-011>024.
RI...Flood Watch from Saturday morning through Sunday morning for 
     RIZ001>008.
MARINE...Gale Watch from Saturday afternoon through Monday morning for 
     ANZ230>237-250-251-254>256.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory until noon EDT today for CTZ002.
     Flood Watch from 8 AM EDT this morning through Sunday morning 
     for CTZ002>004.
MA...Winter Weather Advisory until noon EDT today for MAZ002>004-
     008>011-026.
     Flood Watch from 8 AM EDT this morning 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 from 8 AM EDT this morning through Sunday morning 
     for RIZ001>008.
     Wind Advisory from 5 PM this afternoon to 11 PM EDT this 
     evening for RIZ005-007.
MARINE...Gale Watch from this afternoon through Monday morning for 
     ANZ230>237-250-251-254>256.

&&

$$

SYNOPSIS...Belk/RM
NEAR TERM...Belk/Dooley/RM
SHORT TERM...RM
LONG TERM...Belk
AVIATION...Belk/Dooley/RM
MARINE...Belk/RM
HYDROLOGY...RM
      

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