Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 272334
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
734 PM EDT Wed Mar 27 2024

.SYNOPSIS...
A frontal wave will bring more widespread rain to the region from
late today through Thursday, and possibly lingering into early
Friday. This additional rainfall may lead to renewed flooding
concerns. Rain coming to an end Friday may finish as a quick
burst of low impact snow. Sunny, but windy, Friday and Saturday
with a chance for a few showers Sunday night. Mix of clouds and
sun on Sunday and Monday with near to above normal temperatures.

&&

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

Widespread shower activity has overspread much of western MA and
central CT, though is very slow to progress east of the I-95
corridor where outside of a sprinkles, rain should hold off
through ~ 10 or 11pm. Interestingly, some lightning strikes were
observed to our north near Concord NH over the last hour, but
widespread convective elements are not expected with the showers
overnight. Off and on showers can be expected for most
overnight with stratiform rain developing by daybreak.

Previous Update...

Clouds had dissipated across quite a bit of central
southern New England, but more clouds are waiting just off to
the west. Steep inversion remained in place, along with the
humidity below it. Thus, clouds should be quick to return past
sunset and temperatures drop. Widespread rainfall still expected
to overspread southern New England between 10 PM and 2 AM.
Could be a little earlier along and west of the CT River.

Thinking rainfall tonight will be on the lighter side, generally
one half inch or less.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Key Messages...

* Widespread rain likely
* Axis of heaviest rain remains uncertain

Latest guidance suite still has some issues with the axis of the
heaviest rainfall Thursday into Thursday day. Now looking like
there may be two axes of heavier rainfall. One would be over the
ocean towards the outer Cape and east of Nantucket, so not much
of a concern. The other looks to be right where we would not
want it, eastern CT, northwest RI, and portions of eastern MA.
Since this area already had several inches of rain for this past
weekend, will be issuing a Flood Watch for portions of southern
New England.

Right now, thinking that 1-2 inch rainfall amounts would be most
likely. However, ensembles do suggest a 30-50% probability for
more than 2 inches of rainfall across RI and portions of
southeast MA. Should that amount of rainfall occur, it is
possible that more significant river flooding would result.
Will need to closely monitor this potential over the next 24-36
hours.

Not much wind for this rain event. So the focus is all on the
rainfall and potential flooding.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Highlights

* Rain comes to an end Friday morning and may briefly transition
  to snow as low pressure departs into the Gulf of Maine

* Blustery conditions Friday into Saturday will lead to sunnier
  conditions to start the weekend

* Unsettled conditions mid week next week garner our next
  significant precip chance

Friday and Saturday...

Inverted trough/low pressure gradually swings to our
east/northeast Friday allowing precipitation to come to an end
by around lunchtime. It`s possible that there is a brief period
of snow wrapping around cyclonic flow as 850mb temps drop to as
cold as -6 behind the departing low. Given warm antecedent
conditions and a very saturated ground, thinking that some of
the Hi-Resolution solutions, like the HRRR and NAM12 are much to
aggressive with their 10:1 snow accumulation forecasts of
3-6"+, and even with their positive snow depth change estimates
of up to 2-3" of snow across parts of eastern MA, but would not
be shocked to see a few 10ths of an inch of snow accumulate
across the high terrain before precip ends around mid day.

Blustery conditions will develop late Friday and will maintain
overnight Saturday through mid day as pressure gradient remains
quite tight on the back side of the low. Additionally, a 925mb
jet of 40-50kt will mix to the surface, yielding gusts in the
30-35kt range, with gusts to 40kt possible across the highest
terrain of the Berkshires. Will note the NBM guidance was quite
high compared to other models, which has been the case in
estimating wind gusts as of late, so, blended in the NBM1 10th
percentile guidance to keep gusts below wind advisory criteria.
It`s not out of the question that we see the strongest axis of
the LLJ shifts a bit west would allow more widespread 40kt gust
to develop, thus, not completely ruling out the potential need
for a wind advisory for the period.

The column dries pretty rapidly thanks to brisk NW flow,
yielding sunny skies the second half of Friday through the first
half of the weekend; a welcome sight for southern New
Englanders after a mostly cloudy week. May see some spotty rain
showers overnight Saturday as a weak shortwave tracks across
northern New England.

Sunday and Monday...

Winds subside to around 20kt by Sunday as gradient slackens and
more zonal mid level flow develops. Should see a mix of clouds
and sun on Sunday and Monday as PWATs surge to near a half an
inch, with moisture concentrated between the top of the boundary
layer and 700mb. Mid level ridging building from the west lat
Sunday into Monday will bring above normal temps back to
southern New England, with temps approaching the mid 50s by
Monday afternoon!

Mid Next Week...

Unsettled weather returns mid next week as low pressure digs
from southern Ontario before emerging off the southern New
England coast sometime between late Tuesday and Thursday. At
this time, there remains significant uncertainty in the timing
of this system, but we would be remiss to not at least mention
the possibility of some mixed precipitation, especially across
the high terrain, as cold air infiltrates the region on
north/northeast flow.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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



Tonight...high confidence.

MVFR/VFR at 00z, lowering to IFR/MVFR as showers overspread the
region tonight. LIFR possible across the hilly terrain of CT and
MA. Light SSE winds.

Thursday and Thursday night...high confidence.

Widespread IFR/LIFR in rain, heavy at times possibly across
eastern CT into RI and eastern MA. Light/variable wind becoming
NNE.

KBOS TAF...High confidence in trends, some uncertainty in exact
timing of details. MVFR quickly degrading to IFR/LIFR this
evening. Rain should hold off until ~04Z tonight as stratiform
rain impacts the terminal through much of the period. Very light
winds take on a slight NNE direction tomorrow morning, with
winds generally less than 5kt much of the day.

KBDL TAF...High confidence in trends, some uncertainty in exact
timing of details. Rain will persist through at least 00Z
tomorrow, but may be scattered in nature through sunrise before
becoming more stratiform. Very light to calm winds much of the
day given how slow this cold front is moving.

Outlook /Friday through Monday/...

Friday: Mainly VFR, with local MVFR possible. Windy with gusts
up to 30 kt. Chance RA.

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

Saturday Night: VFR. Windy with local gusts up to 30 kt. Slight
chance RA.

Sunday through Sunday Night: VFR. Breezy.

Monday: VFR. Slight chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

* NNE winds finally shift to the SSE Wed afternoon
* Heavy rain possible late tonight into Thursday Night

Weak high pressure remains over the waters into tomorrow. Showers
become widespread, limiting vsby. Low pressure intensifies at it
moves offshore Thursday into Thursday night. Rain, heavy at
times, limits vsby.

Outlook /Friday through Monday/...

Friday: Strong winds with gusts up to 30 kt. Rough seas up to
10 ft. Chance of rain.

Friday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 10 ft. Slight chance of rain.

Saturday: Strong winds with gusts up to 35 kt. Areas of rough
seas.

Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain.

Sunday through Sunday Night: Winds less than 25 kt. Areas of
seas approaching 5 ft.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from 2 AM EDT Thursday through late Thursday night
     for CTZ004.
MA...Flood Watch from 2 AM EDT Thursday through late Thursday night
     for MAZ004>007-012>024-026.
RI...Flood Watch from 2 AM EDT Thursday through late Thursday night
     for RIZ001>007.
MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ250.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ251.
     Small Craft Advisory until 8 PM EDT Thursday for ANZ254>256.

&&

$$

SYNOPSIS...Belk/KS
NEAR TERM...Belk/KS
SHORT TERM...Belk
LONG TERM...RM
AVIATION...Belk/KS
MARINE...Belk/KS


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