River Flood Warning 16, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
1223 AM EST Fri Jan 12 2024

.SYNOPSIS...
Dry weather persists through tomorrow with seasonable to
slightly above normal temperatures. A number of area rivers and
streams remain swollen or out of their banks, and limited
recession in river levels is expected through the end of the
workweek. Another powerful storm system then impacts the region
tomorrow night into Saturday, bringing a renewed or worsened
risk for areal and river flooding, strong southeast winds and
coastal flooding. Turning colder and also windy Saturday night
into Sunday. Much of next week will feature cold/below normal
temperatures with perhaps a winter storm around Tuesday...but
still the possibly that this system could pass harmlessly out
to sea.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Update: 1005 PM

Overall the forecast remains in good conditions with little
changes made. Did adjust sky cover and hourly temperatures based
on the latest observations.

During this update, cancelled the flood warning for the
Blackstone River at Woonsocket and the Neponset River at Norwood
as river levels feel below minor flood stage.

Tonight and Tomorrow

Upper level shortwave energy will generate some scattered to
broken clouds this evening especially across the interior.
There may even be a few snow showers/flurries mainly in far
western MA and especially the Berks.

Otherwise...high pressure builds over the region tonight and
tomorrow. This will result in diminishing westerly winds and
clearing skies across most of the region. Some low to mid clouds
may linger over the northwestern areas through tomorrow
afternoon. Temperatures will be slightly above normal during
this period with lows overnight in the middle 20s to the lower
30s and highs tomorrow afternoon in the 40s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tomorrow Night

* Strong storm to bring more wind, rain, and flooding to
  southern New England Friday night into Saturday.

The highlight of the short-term forecast will be another inland
track low-pressure system that is forecast to bring another round of
rain, strong south/southeasterly winds, and flooding to southern New
England this weekend. A parent low will be intensifying through the
day tomorrow as it treks across The Midwest and over The Great
Lakes. This will support the development of a secondary low over The
Mid-Atlantic states that will move over The Northeast with strong
south/southeasterly winds and moderate to heavy rainfall. The storm
is forecast to peak roughly between 1AM and 7AM Saturday when 1 to 2
inches of rain will fall across the region with the highest amounts
focused across eastern CT and RI. A robust 70-80 knot jet at 925 hPa
will also be moving over the region at this time which should be
strong enough to support 45 to 60 mph wind gusts at the surface.
Similar to the event we experienced earlier this week, the strongest
winds will be focused along the coastal areas with peak winds
expected to be observed over The Cape/Islands. A high wind watch is
in effect for the entire coastline of southern New England. While
the peak winds will occur overnight Friday into Saturday morning,
gusty west winds will persist through the weekend. In addition to
the high wind watch, we have watches in effect for storm force winds
over the coastal waters, a flood watch for fresh water flooding, and
a coastal flood watch for the entire coastline including The
Islands. Please see the Hydro, Coastal Flood, and Marine sections
below for more information on these hazards.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Points:

* Rain ends by mid morning Sat, otherwise quite breezy & very mild
* Windy/Colder Sat night & Sun with a few snow showers on Sun
* Blustery and cold for the upcoming work week with below normal temps
* Winter Storm potential Tue but system could also pass out to sea

Details...

Saturday...

Powerful low pressure system sub 975 mb across the eastern Great
Lakes early Saturday will be lifting northeast into Quebec during
the day. Strong SSE low level jet will bring the potential for
strong to damaging wind gusts along the coast early Sat AM.
However...this will be quickly pushing east of the region as the
powerful low lifts into Canada. This will bring an end to the rain
and the potentially strong to damaging wind gusts along the coast
early Sat AM.

Otherwise...as the low lifts into Quebec a drier southwest flow of
air will work into this region. This should result in mainly dry
weather...although we can not rule out a brief spot shower in
association with the upper level shortwave the rest of the day. 925T
are quite mild late Sat AM still on the order of +5C to +9C. This
coupled with good mixing on southwest flow should allow for highs to
reach well into the 50s and even the low risk for briefly touching
60 across parts of the coastal plain. Good mixing developing should
yield southwest wind gusts of 25 to 40 mph.

Saturday night & Sunday...

Closed upper level low extending from the eastern Great Lakes into
eastern Canada will result in a WSW flow of air into southern New
England. This will allow progressively colder air to work into
southern New England from the west. The delivery on west to
southwest flow is not ideal for southern New England to get bitterly
cold because it modifies...but definitely more January-like. Low Sat
night will mainly be in the 20s to the lower 30s. Highs on Sun
should mainly be in the middle to upper 30s across the interior high
terrain...to near 40/lower 40s over much of the coastal plain.

The bigger story Sat night and Sun will be the persistence of windy
conditions. Bufkit soundings show ideal mixing as colder air aloft
supports rather steep lapse rates. Thinking a long duration of west
to southwest wind gusts on the order of 35 to 50 mph. Therefore...we
may need some Wind Headlines over this time frame. Mainly dry
weather should prevail...but a few snow showers are possible
Sunday with fairly strong shortwave energy aloft and steep lapse
rates. Low risk for even a heavier snow squall or two.

Monday through Thursday...

A much colder setup is on tap for our region next week. A -EPO/-NAO
pattern will force the arctic airmass that will be invading western
Canada and the central Plains to advance eastward. Now the delivery
of this airmass is from the west...which is not an ideal direction
for it to maintain its magnitude. So while we expect much colder
weather compared to what we have seen most of the winter...it will
not be to the extreme levels than other parts of the country will
see. Nonetheless...temps will average below normal with highs mainly
in the upper 20s to the middle 30s and overnight lows mainly in the
teens to the lower 20s much of next week.

The main thing will need to watch is the potential for a Winter
Storm around the Tuesday time frame. This is 5 days in the
future...so plenty of uncertainty on what might happen. Appears the
amplitude & timing of northern and southern stream energy will be
the key components. Most of the guidance has been leaning towards a
partial phase...where low pressure cuts underneath us and brings
accumulating snow with perhaps some Ptype issues for a time on the
coastal plain. While this is the most likely scenario...the 12z
ECMWF along with a few of the GEFS/EPS ensembles show the potential
for lack of phasing allowing the low passes harmlessly out to see
with just dry and cold weather. The third scenario is more of a
complete phase with a stronger system with much higher QPF...but
also the potential for a further northwest track and more Ptype
issues.

In a nutshell...we will need a few more days to sort this all out.
But appears at least a decent shot for accumulating snow for much of
the region.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

06z TAF Update

Through 12z... High confidence.

VFR. West/Southwest winds 5 to 10 knots.

Friday... High confidence.

VFR. West winds should become light SE between 18z and 00z.

Friday Night...High confidence in trends but moderate confidence
in timing.

Conditions deteriorating to IFR/LIFR between 00Z and 06Z
Saturday as heavy rainfall and strong south/southeast winds
overspread the region. 30 knot southeast wind gusts at the
interior terminals with 40 to 50 knot gusts possible near the
coast and Islands.

KBOS TAF... High confidence.

KBDL TAF... High confidence.

Outlook /Saturday Night through Tuesday/...

Saturday: MVFR/IFR conditions possible. Strong winds with gusts
up to 50 kt. RA, chance SHRA.

Saturday Night: VFR. Strong winds with gusts up to 45 kt.

Sunday: VFR. Strong winds with gusts up to 45 kt. Slight chance
SHSN.

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

Martin Luther King Jr Day: VFR. Breezy.

Monday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SN.

Tuesday: Mainly IFR, with areas MVFR possible. Breezy. Chance
SN, chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight and Tomorrow

Gusty west/southwest winds slowly diminish to more modest levels
overnight as high pressure builds south of the coastal waters. Calm
conditions should persist through early Friday afternoon before
winds begin to increase out of the east/southeast ahead of a strong
low-pressure system.

Tomorrow Night

A storm watch in in effect for the coastal waters tomorrow night
into Saturday. Storm force south/southeast winds are forecast to
develop over the coastal waters as a strong low-pressure system
moves over the northeast. 45 to 50 knot wind gusts will be possible
which will create extremely dangerous marine conditions. This will
also support seas building to 10 to 15 feet over the outer marine
zones by Saturday morning. Seas will likely continue to build into
Saturday evening.

Outlook /Saturday Night through Tuesday/...

Saturday: gale force winds with gusts up to 45 kt. Rough seas
up to 16 ft. Rain, chance of rain showers.

Saturday Night: gale force winds with gusts up to 45 kt. Rough
seas up to 16 ft.

Sunday: gale force winds with gusts up to 45 kt. Rough seas up
to 13 ft. Slight chance of rain showers.

Sunday Night: Low risk for gale force winds with gusts up to
45 kt. Rough seas up to 11 ft. Local visibility 1 to 3 nm.

Martin Luther King Jr Day: Low risk for Small Craft Advisory
winds with gusts up to 25 kt. Local rough seas.

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of snow, slight chance of rain. Visibility 1 to
3 nm.

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Chance of rain,
chance of snow. Areas of visibility 1 to 3 nm.

&&

.HYDROLOGY...
A Flood Watch remains in effect for all of southern New England
through Saturday evening. Many area rivers and streams are still
experiencing minor to moderate river flooding that was triggered
from last weeks heavy rainfall. Another 1 to 2+ inches of rainfall
is forecast to fall over southern New England Friday night through
Saturday as another strong low-pressure system moves over The
Northeast. The area of greatest concern is eastern CT and RI where
the heaviest precipitation is forecast to fall. The additional
rainfall is expected to prolong or exacerbate the ongoing fresh
water flooding across the region.

&&

.TIDES/COASTAL FLOODING...
A Coastal Flood Watch remains in effect for the entire southern New
England coastline. Another strong low-pressure system is forecast to
move over The Northeast with powerful south/southeast winds that
are likely to produce a 2 to 3 foot storm surge along the southern
New England coastline. This is likely to produce minor to moderate
flooding for several locations in southern New England. The degree
of coastal flood impacts will hinge on the timing of strongest
winds/peak surge aligning with astronomical high tides. Latest
surge guidance suggests peak-surge will occur close to the Saturday
morning high tide along the south coast where moderate flooding will
be most likely. Along the east coast however, a peak surge close to
3 feet is forecast to occur closer to low-tide. Nonetheless, surge
values are still forecast to be close to 2 feet by the early
Saturday afternoon high tide along the east-coast. This may still be
enough to produce minor to moderate coastal flood impacts at
locations such as Boston and Scituate MA. Both Marthat's Vineyard
and Nantucket will be at risk for minor to moderate coastal flooding
as well. Coastal flood watch may be upgraded to a coastal flood
warning if confidence in at least moderate coastal flood impacts
grows.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch through Saturday evening for CTZ002>004.
MA...Flood Watch through Saturday evening for MAZ002>021-026.
     High Wind Watch from late tonight through Saturday afternoon
     for MAZ007-015-016-018>024.
     Coastal Flood Watch from Saturday morning through Saturday
     afternoon for MAZ007-015-016-019-022>024.
     Coastal Flood Watch from Saturday morning through Saturday
     afternoon for MAZ020-021.
RI...Flood Watch through Saturday evening for RIZ001>007.
     High Wind Watch from late tonight through Saturday afternoon
     for RIZ004>008.
     Coastal Flood Watch from Saturday morning through Saturday
     afternoon for RIZ002-004>008.
MARINE...Storm Watch from late tonight through Saturday afternoon for
     ANZ230>237-250-251-254>256.
     Small Craft Advisory until 7 AM EST this morning for ANZ235-
     237-250-254.
     Small Craft Advisory until 1 PM EST this afternoon for ANZ255-
     256.

&&

SYNOPSIS...Frank/RM
NEAR TERM...Frank/Dooley/RM
SHORT TERM...RM
LONG TERM...Frank
AVIATION...Frank/Dooley/RM
MARINE...Frank/RM
HYDROLOGY...RM
TIDES/COASTAL FLOODING...RM