Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 231925
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
325 PM EDT Sat Mar 23 2024

.SYNOPSIS...

Heavy rain today, exiting by midnight. Drying out Sunday into early
next week but rather windy along the coast, especially Cape and
Islands.Cooler with breezy to gusty northeast winds Monday and
Tuesday, and chances for light rain showers expanding westward
from the offshore waters. Building rough seas are likely Monday
and Tuesday over the southeastern waters. It remains unsettled
through mid to late in the week, with rain chances returning
Wednesday night into Thursday, and a better chance around late
Thursday and into Friday. Temperatures trend above normal for
mid to late in the week.


&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

The low bringing us all this rain is currently centered over the
Delmarva, poised to lift into our offshore waters and slide along
the south coast then over the Cape Cod canal this evening and
overnight. The excessive rainfall is the result of a strengthening
low level jet coinciding with moist inflow off the Atlantic combined
with large scale ascent thanks to placement beneath the entrance
region of a 150 kt upper jet. This sets up a good pattern for heavy
rainfall, with HREF guidance indicating the period of heaviest rain
being generally 4pm-10pm with potential for as much as 1-2 inches in
3 hours for a brief period from coastal CT to RI to southeast MA.
The Flood Watch remains in effect for some river flooding and the
potential for urban/poor drainage flooding as well. The previously
mentioned low level jet kicks in in earnest this evening with gusts
to 40-50 mph. The cold front then drops through and colder air
filters in on the back end. However, dry air also quickly moves in,
so any changeover back to snow should be very brief with little to
no impact. Rain comes to an end from west to east between 10pm and
2am. Winds quickly shift to the northwest and remain gusty
overnight, gusting 25 to 35 mph.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...

Sunday will be dry but blustery thanks to our placement between a
strong low well south over the Atlantic and high pressure over the
Great Lakes. This also produces winds out of the northeast which
will serve to keep moisture (clouds) over eastern MA, potentially
into RI and even eastern CT tomorrow. Further west expect even more
sun. Winds gusting 25 to 35 mph will make highs in the upper 30s
feel more like upper 20s/low 30s. The gradient only tightens
overnight as the storm passes closer to SNE and this will mean
deteriorating conditions on our southern and eastern waters with
wind gusts to 35 to 45 kts and seas of 12-14 ft.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

Highlights:

* Temps near or slightly cooler than normal Mon and Tue, with
  northeast breezes/gusts. Light showers offshore expanding westward
  Mon night/Tue?

* Likely very choppy, rough seas over southeast waters Mon and Tue.

* Remains unsettled mid to late week with chances for rain Wed
  night/Thu and a better chance Thu night/Fri. Temps trend
  near/above normal.

Details:

Monday and Tuesday:

Rather prolonged period of onshore NE flow, with a tightening
pressure gradient driven by a 1040 mb high pressure area over
northeast Quebec and a nearly vertically-stacked but strong coastal
low over 35N/68W lat/lon vicinity. Sfc ridge axis from the high is
expected to extend southward through the mid-Atlantic states and
Carolinas, though it tends to weaken as we move through time. With
that said, there remains considerable disparity on when this ridge
axis starts to weaken, which would influence the northward return of
showers and how far west any showers may extend.

The tightening NE pressure gradient will bring stiff NE winds to
eastern and especially southeastern portions of Southern New
England. NE gusts around 35 to 45 mph take place over eastern and
southeast MA and RI and around 20-30 mph inland. Though this wind
will bring a bit of chill, the persistent NE gradient and stable
fetch region seem more likely to bring some impact for marine and
coastal interests, with building seas and winds gusting to gale
force. Rough, choppy seas building to 12-14 ft are expected and
though it`s not beach season, could be some surf/beach erosion
issues along east-facing shorelines, especially Cape and Islands.

With the stated uncertainty in how any offshore moisture/related
showers expands landward and further inland, kept PoP lower than the
high-chance NBM values; GFS would favor a shutout entirely, although
some consensus in the GEM/ECMWF in showing westward-spreading and
light rain showers Mon aftn along the coast, then further inland
into Tue/Tue night. PoPs will need adjusting, either up or down, as
we move through time, but rain amts look light and wouldn`t be
necessarily impactful.

Despite slowly rising 925-850 mb temps, a limited mixing depth and
more clouds further south and east will likely favor slightly below
normal high temps and slightly above normal low temps for each day.
Overall a pretty chilly, raw couple days are likely with the NE
breezes, especially nearest the coast.

Wednesday through Friday Night:

Ridging aloft between the distant/offshore coastal low and a broad
upper trough over the east-central CONUS weakens considerably early
Wed. The broad trough gradually shifts eastward and sends a couple
periods of rain showers to our area. One focused period looks to
take place Wed night/early Thurs as a cool front moves east. Then a
somewhat better chance later Thurs into Fri as the cool front stalls
offshore and induces low pressure near the Carolinas to move NNE
into the mid-Atlantic and coastal New England. PoPs were highest in
this latter period in the 45-60 percent range, higher east. Still
uncertain in some of the details and how quickly rain would shift
eastward/offshore, but the mid to late week period looks pretty
unsettled.

Temps trend near to above normal, with highs in the upper 40s/low
50s and lows in the mid/upper 30s.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

18Z update...

This afternoon...High confidence in trends.

Rain will pick 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 02Z to 09Z. Rain lingers a bit longer
over The Cape/Island terminals likely tapering off between 04
and 07Z with VFR returning. 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.

Sunday night...High confidence.

VFR. Northeast winds 15 to 20kts, gusting to 30 kts just
offshore.

KBOS TAF...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...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 /Monday through Thursday/...

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

Monday Night: Mainly VFR, with local MVFR possible. Strong
winds with local gusts up to 40 kt.

Tuesday: Mainly VFR, with local IFR possible. Windy with gusts
up to 35 kt.

Tuesday Night: Windy with areas of gusts up to 30 kt. Chance
RA.

Wednesday through Wednesday Night: Chance RA.

Thursday: Breezy. 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

Tonight: A cold front moves over the waters tonight. 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.

Sunday night: Low pressure passing to our south will increase
gusts and seas. NE winds 20-35 kts gusting 35 to 40 kts with
seas increasing to 12-14 ft.

Outlook /Monday through Thursday/...

Monday: Moderate risk for gale force winds with gusts up to
45 kt. Rough seas up to 15 ft. Slight chance of rain.

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 14 ft. Slight chance of rain.

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

&&

.TIDES/COASTAL FLOODING...
There is some concern for Narragansett Bay during the high tide this
evening but confidence has grown that th core of the jet stays
just to the east and so the surge will likely be limited to
1.5-2 ft which will keep water levels below flood. A Coastal
Flood Statement is in effect. The worst case scenario is for
pockets of minor flooding.

&&

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

&&

$$

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


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