Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 241716
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
116 PM EDT Sun Mar 24 2024

.SYNOPSIS...
Mainly dry today and Monday but windy along the coast,
especially Cape and Islands. Then an unsettled pattern for
Tuesday through Friday with multiple chances of rain. Moisture
from the ocean backs into the region Tuesday with focus for
light rain across eastern New England, then showers region wide
on Wednesday. A coastal low pressure may then bring more
widespread rain sometime Thursday into Friday. Drying out next
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...

Forecast is on track with the main adjustment being to lower
temps a few degrees as we`ve not warmed up quite as much as
expected; should top out in the upper 30s to near 40.

Previous Discussion...

Highlights:

* Chilly despite sunshine making a return. Trending towards a more
  sun-filled day, but the sky will have a milky-white look due to
  higher clouds across eastern Massachusetts and Rhode Island.

* SPS issued through 8am for possible icy conditions as temperatures
  are expected to fall below freezing. Motorists and pedestrians
  should exercise caution if heading out on the roadway overnight as
  untreated surfaces may become slick.

The system that brought widespread 2-3 inches of rainfall yesterday
is now racing north into the Canadian Maritime. For us, surface high
pressure is building in out of the west. Given our position between
the two systems, there is a rather tight pressure gradient, thus the
continued gusty conditions. After reviewing latest high-res guidance
in BUFKIT, did opt to extend the Wind Advisory for Cape Cod and the
Island through 6AM as there could be periodic gusts to 50 MPH. The
stronger gusts end this morning with the rest of the day featuring a
north/northwest gust 25 to 35 MPH. Elsewhere, the wind gust are
between 15 and 25 MPH.

It will be a dry day, though expect the larger rivers to continue to
rise due to the runoff from smaller creeks and streams finally
reaching these larger rivers.

Sunshine returns, though it likely is more of a milky-white sky
across eastern Massachusetts and possibly into Rhode Island. These
high clouds are the outer fridge of the departing low pressure
system from yesterday.

Despite the sunshine, temperatures will remain below normal once
again with afternoon high temperatures only reaching the upper 30s
to low 40s. The normal high for late March are between 45 and 50
degrees.

&&

.SHORT TERM /MONDAY/...
Highlights:

* Generally dry period with below normal temperatures.

A quiet night ahead with surface high pressure expanding over
Quebec. Mainly clear sky cover to the west and easing winds will
help temperatures fall well into the mid-teens, while the coastal
plain of Massachusetts and Rhode Island are noticeably `warmer` with
overnight low temperatures in the upper 20s to mid 30s. Part of what
keeps this area warmer is the mix boundary layer, with a north to
north/northeast wind 10 to 15 MPH. During the overnight hours a
coastal low pressure system moves north but will likely get `stuck`
southeast of the Benchmark due to the surface high over Quebec
strengthening to 1040mb.

Once again, we are situated between two pressure systems,
increasing the wind speeds. Do anticipate the more gusty winds, up
to 35 mph, are felt across southeast Massachusetts, Cape Cod, and
Islands through Monday afternoon. Over all a dry day. Depending on
how far north and west the 995mb low can reach will dictate whether
or not we see light rain for some areas of southeast Massachusetts.
Ensembles show less than 20 percent of 0.01 just off shore, mainly
outer Cape Cod and Nantucket. Kept POPs at slight chance or less for
Monday afternoon for sites like; MVY, ACK, HYA, and CHH.

As for temperatures, the northeast flow will keep 925mb temperatures
fairly low, -4C to -6C, around 10th percentile, based off sounding
climatology from CHH. Afternoon highs reach the low and mid 40s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights:

* Below normal temps Tue, with spotty light rain expanding westward
  across eastern half SNE

* Milder Wed with showers at times

* A coastal storm may bring more rain Thu into Fri

Monday night into Wednesday...

Stagnant pattern persists into Tue with SNE caught between Maritimes
high pres to the north and ocean storm well to the south. Gusty NE
winds will continue into Tue while deeper moisture begins to back in
from the east. This can be seen with plume of higher 1"+ PWATs
expanding westward toward New Eng. This will lead to increasing
chances of light rain developing over the Cape/Islands by late
Monday night then pushing west into eastern New Eng Tue. Some
uncertainty remains how far west the moisture gets, but higher
confidence in at least some spotty light rain for eastern half of
SNE on Tue and rest of the region Tue night. Then on Wed, weak
ridging aloft breaks down as broad longwave trough approaches from
the west sending weak impulses and increasing toward New Eng within
the SW flow aloft. So another unsettled day Wed with a few showers
at times. Certainly not a washout for Tue/Wed but it will likely be
wet at times with lots of low clouds. Below normal temps Tue with NE
flow and cloud cover holding temps in the upper 30s to mid 40s, then
milder Wed as global ensembles indicate high probs of temps in the
50s.

Thursday through Saturday....

More wet weather expected Thu into Fri as a fairly robust southern
stream shortwave rotating around the longwave trough leads to
developing low pres tracking NE along the eastern seaboard. There is
obvious uncertainty with the track of low pres at this time range
and where axis of rainfall sets up as well as timing of when rain
exits. GEFS, ECMWF and CMC ensembles all indicate high probs of
0.50"+ QPF Thu into Thu night, and at least moderate probs of 1"+
QPF for SE New Eng so it is looking wet during this time. Rain may
be pushing offshore during Fri but timing of when this occurs is
uncertain so we kept PoPs going through Fri. It appears we finally
dry out next Sat as trough axis lifts to the NE with dry NW flow
developing.

&&

.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

18Z update...

This afternoon through Monday night...High confidence.

VFR. Expecting a lull in gusts this afternoon/evening but
another round of 25-35kt gusts is expected overnight into Mon.
Otherwise, VFR through Monday night.

KBOS TAF...High confidence.

KBDL TAF...High confidence.

Outlook /Tuesday through Thursday/...

Tuesday: MVFR/IFR conditions possible. Windy with gusts up to
30 kt. Chance RA, slight chance FZRA.

Tuesday Night: Mainly IFR, with areas VFR possible. Breezy.
Chance RA, slight chance FZRA.

Wednesday: MVFR/IFR conditions possible. Chance RA.

Wednesday Night: Mainly MVFR, with local IFR possible. Chance
RA.

Thursday: MVFR/IFR conditions possible. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today: Dry conditions. Low pressure system to the north continues
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.

Tonight: Low pressure developing to the south will increase gusts
and seas. NE winds 20-35 kts gusting 35 to 40 kts with seas
increasing to 12-14 ft.

Monday: Low pressure system moves north and continues gusty NE gales
on the southern and eastern outer waters. Northeast waters gusts
near 30 knots. Seas on the outer waters are greater than 14 feet,
near shore waves are 6 to 10 feet.

Outlook /Monday Night through Thursday/...

Monday: Low risk for gale force winds with gusts up to 40 kt.
Rough seas up to 15 ft.

Monday Night: Strong winds with gusts up to 40 kt. Rough seas
up to 15 ft. Slight chance of rain.

Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to
14 ft. Chance of rain.

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 12 ft. Chance of rain.

Wednesday: Winds less than 25 kt. Rough seas up to 9 ft. Chance
of rain.

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

Thursday: Winds less than 25 kt. Seas up to 5 ft. Rain likely.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT Monday for ANZ230-231-236-
     237-251.
     Gale Warning from 1 AM to 8 PM EDT Monday for ANZ232>235.
     Gale Warning until 8 PM EDT Monday for ANZ254>256.

&&

$$

SYNOPSIS...KJC/Dooley
NEAR TERM...BW/Dooley
SHORT TERM...Dooley
LONG TERM...KJC
AVIATION...KJC/BW
MARINE...KJC/Dooley


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