Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 261727
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
127 PM EDT Tue Mar 26 2024

.SYNOPSIS...
Another chilly day is on tap for Tuesday, with raw northeast winds
along with some spotty light showers, drizzle and fog, especially
across eastern Massachusetts. Considerably milder Wednesday,
but continued risk for showers. A frontal wave will bring more
widespread rain Thursday into early Friday, which may lead to
renewed flooding concerns. Drying out later Friday into
Saturday, but there remains uncertainty in the exact timing.
Dry and seasonable next weekend, but blustery on Saturday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Damp, cool day in progress this morning with most locations
reporting temperatures in the 30s and drizzle/rain from
Providence east. This cold, moist onshore flow will continue
throughout the day. Forecast is on track.

Previous Discussion...

Key Points...

* Cool/Raw Tue with spotty light showers/drizzle, esp eastern MA
* Highs Tue only in the upper 30s/lower 40s

Details...

Tuesday...

Occluded low well south of New England begins to rotate deeper
moisture into SNE today, especially across eastern MA via WAA aloft
wrapping cyclonically around the offshore. This combined with moist
ENE low level flow into SNE, will result in bands of light
showers coming onshore, along with areas of drizzle and fog.
Not a washout, but definitely nuisance precip across
eastern/central MA into RI, with precip not as widespread
westward into CT and western MA.

Raw/damp ENE winds 15-25 mph, except gusts up to 35 mph Cape Cod and
Islands continue today, slowly easing late in the day as pressure
gradient relaxes. However, this will result in another chilly day
with highs only in the upper 30s to lower 40s, mid 30s high terrain.
These temps are about 10 degs cooler than normal. It will feel
coolest along/near the coast given the chilly onshore winds.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
2 AM update...

Key Points...

* Remaining damp Tue night
* Milder Wednesday and not as wet

Tuesday night...

Synoptic scale lift arrives later tonight in response to s/wv trough
approaching from the west. However, deep layer moisture is lacking
and this should preclude widespread showers, hence more
scattered in areal coverage, along with areas of drizzle and
fog. Thus, damp weather at times. Not as chilly as airmass
slowly modifies. Lows in the 30s. As previous forecaster noted,
the higher terrain could see lows near freezing. Thus, low risk
of spotty light freezing rain/drizzle at the highest elevations
of the Worcester Hills and east slopes of the Berks. Although,
with cold air damming setup weakening overnight, probability is
very low for any freezing rain/drizzle. Otherwise, ptype will be
all rain. Light NE winds become light and variable late.

Wednesday...

Some synoptic scale lift moving across SNE from S/WV energy in the
SW flow aloft, but deep layer moisture is lacking. Thus, other than
morning drizzle and fog, late morning into the afternoon should
feature mainly dry weather, especially across RI and eastern MA.
Farther to the west, deeper moisture may result in scattered
showers across western MA/CT.  Clouds likely dominate but
milder, in response to low level flow becoming SSE, supporting
highs in the mid to upper 50s. It will feel milder as dew pts
climb into the 40s, compared to the 20s early Tue. Light and
variable winds early becoming SSE in the afternoon.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Highlights

* Heavy precipitation late week may lead to an elevated risk for
  flooding across southeastern MA and Rhode Island

* Trending drier with near normal temperatures this weekend


Wednesday night through Friday

An active period of weather develops late Wednesday into Thursday as
a robust short-wave trough digs into the southeastern US. This will
support the development of an elongated region of low pressure
nearly parallel to the east coast that will track north/northeast
through the end of the week. A strong region of frontogenesis
oriented north to south is forecast to develop within the trough
axis and extend from the Carolinas to southern New England. As the
upper-level short-wave trough becomes negatively tilted early
Thursday, the elongated region of low-pressure will slowly track
north/northeast through Friday. With above normal moisture situated
over southern New England (PWAT ~1.25 inches) , this synoptic setup
may support a steady period of rain over southern New England from
roughly Wednesday night through Friday morning.

Latest ensemble mean precipitation forecasts are indicating the
potential for a widespread 1 to 3 inches of rainfall between
Wednesday night and early Friday afternoon. Currently, southeast MA
and RI are in the bullseye for model precipitation with ensemble
means between 2 and 3 inches. If we consult ensemble probabilities
from the LREF and NBM, there is above a 30 and 50 % chance
respectively between the two ensembles for 24 hour precipitation to
exceed 2 inches across southeastern MA and RI between Thursday and
Friday morning. With several rivers in these locations already in
flood stage, additional rainfall of this magnitude may prolong or
exacerbate ongoing flooding. There is still a fair amount of
uncertainty in the forecast given the dynamic nature of the system,
but the ensemble probabilities alone are enough to raise some
concerns for the end of the week. Should confidence in significant
rainfall continue to increase, Flood Watch headlines may be needed
for portions of southern New England. We will have a better idea of
what to expect as we enter the time range of hi-resolution ensemble
guidance during the next 24 to 36 hours.

Aside from the rainfall to end the week, temperatures are forecast
to be near normal with highs in the upper 40s/low 50s and lows in
the upper 30s/low 40s Wednesday night through Friday.

Friday night through the Weekend

The elongated region of low-pressure expected to produce late week
precip will continue to traverse north/northeast to end the week.
North/northwest flow develops behind the system and ushers drier air
over the region that should support partial sunshine for the
weekend. While temperatures will be close to normal in the upper
40s/low 50s on Saturday and Sunday, efficient boundary layer mixing
in the post frontal air mass is likely to support breezy northwest
winds this weekend. Saturday looks to be the windier of the two days
with gusts from 20 to 30 mph possible. Model guidance relaxes the
pressure gradient on Sunday with more modest wind gusts closer to 20
mph. Forecast currently looks quiet to start the week next Monday,
but ensembles suggest there may be more active weather beyond day 7.
Stay tuned for further details later this week.

&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

18Z Update...

This afternoon...high confidence on trends, lower on exact
details and timing.

MVFR/IFR conditions overspread the region from SE to NW today,
with much of the region IFR by late today, with areas of LIFR
possible late across Cape and Islands. Bands of light rain and
drizzle continue. NE winds remain gusty 15-25 kt, except up to
35 kt along the coast, slowly easing late in the day.

Tonight...high confidence.

IFR/LIFR in low clouds, spotty light rain, drizzle and areas of
fog. NE winds ease and become SE late.

Wednesday...moderate confidence.

Drier on Wednesday with IFR/LIFR early imporving to MVFR/VFR by
after non. Light and variable winds in the AM becoming SSE in
the afternoon.

Wednesday night...moderate confidence.

VFR to start lowering to IFR/LIFT in increasingly widespread
moderate rain showers. Light and variable winds becoming
northerly.

KBOS TAF...High confidence in trends, some uncertainty in exact
timing and details.

KBDL TAF...High confidence in trends, some uncertainty in exact
timing and details.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: MVFR/IFR conditions possible. RA likely.

Thursday: Mainly MVFR, with areas IFR possible. RA.

Thursday Night: MVFR/IFR conditions possible. Windy with gusts
up to 35 kt. RA likely.

Friday: Mainly VFR, with local IFR possible. Windy with gusts
up to 35 kt. Chance RA.

Friday Night through Saturday: VFR. Windy with gusts up to
35 kt. Slight chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

2 AM update...

* High Seas & NE Gales Tue Morning...

Tuesday...

Offshore low well south of New England will continue to generate ENE
gales across the MA/RI waters into Tue morning, then slowly
slackening Tue afternoon. Given the large easterly fetch, very
rough/dangerous seas persist, 15-20 ft seas SE of Nantucket and Cape
Cod. Vsby reduced at times in light rain, drizzle and fog.

Tuesday night...

High pressure over the Maritimes and low pressure south of New
England both weaken. This will result in winds slackening and
shifting from NE to SE. Rough seas slowly subside. Vsby limited in
areas of light rain/drizzle and fog.

Wednesday...

Weak high pressure over the waters yielding light and variable
winds. Drizzle and fog during the morning, slowly gives way to drier
weather in the afternoon along with improving vsby.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt. Local rough seas. Rain
likely.

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

Thursday Night: Low risk for gale force winds with gusts up to
35 kt. Areas of rough seas. Rain likely.

Friday: Moderate risk for gale force winds with gusts up to
35 kt. Rough seas up to 9 ft. Chance of rain.

Friday Night: Moderate risk for gale force winds with gusts up
to 35 kt. Rough seas up to 10 ft. Chance of rain.

Saturday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Slight chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230-
     236.
     Gale Warning until 2 PM EDT this afternoon for ANZ231>235-
     254>256.
     Small Craft Advisory until midnight EDT tonight for ANZ237.
     Small Craft Advisory until 8 AM EDT Wednesday for ANZ250-251.

&&

$$

SYNOPSIS...Nocera
NEAR TERM...Nocera/BW
SHORT TERM...Nocera
LONG TERM...RM
AVIATION...BW/RM
MARINE...Nocera/BW


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