Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 281245
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
845 AM EDT Thu Mar 28 2024

.SYNOPSIS...
A frontal wave will bring more widespread rain to the region from
tonight, into Thursday, and possibly lingering into early Friday.
This additional rainfall may lead to renewed flooding concerns.
Rain, possibly mixed with snow ends Friday morning, except
possibly linger into the afternoon across eastern MA. Gradual
clearing Friday, but windy Friday and Saturday, with a chance
for a few showers Saturday night into Sunday morning. A mix of
clouds and sunshine Sunday and Monday with near to above normal
temperatures.

&&

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

850 AM Update...

Key Points Today...

* Widespread Rain with highs in the upper 40s/lower 50s
* Minor poor drainage/urban flooding for the late day commute

Widespread rain already in place will continue through the
afternoon. The heaviest rain will focus itself across the
eastern half of the region...but again rain will continue to
impact the entire region. Previous forecast handles this well
in the explanation below.

Stalled frontal boundary and associated low level convergence
draped across SNE today. Meanwhile, strong upper level jet
streak develops over the northeast into Quebec, with jet
increasing to 130-140 kt. This has enhanced the QG forcing over
SNE and will be acting on a moisture plume with PWATs of 1+
inches. This is courtesy of a full latitude trough approaching
from the west with strong southern stream jet energy rounding
the base of the trough and then rotating up the eastern
seaboard. This will induce a wave of low pressure to develop on
the frontal boundary over FL/GA early this morning, then
intensifying as the wave moves northeast off the Carolina coast
late today. All of these ingredients will continue to result in
a widespread soaking rainfall. Airmass is warm enough to support
ptype of all rain, but this system has winter type attributes,
including strong mid level Fgen over SNE, which will result in
rain moderate to heavy at times.

Not expecting excessive rainfall rates, but a steady light to
moderate rain, heavy at times. Rainfall totals through 8 pm roughly
0.50-1.00 inches regionwide, with locally up to 1.5 inches possible
from eastern CT into RI and eastern MA. Thus, any flooding today
will be limited to minor urban/street/highway flooding,
especially later in the day. Seasonable temps with highs in the
upper 40s to lower 50s. With frontal boundary draped across the
area, light NNE winds over eastern MA/RI and NNW winds in CT
and western- central MA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
245 AM update...

Key Messages Thursday night & Friday...

* Rain continues, moderate to heavy at times
* Rain may briefly mix with or change to snow before ending Friday
  morning

Thursday night...

Trough amplification with negative tilt evolving as it moves
across SNE. This combined with RRQ of upper level jet moving
across the area will enhance QG forcing for ascent, yielding
widespread rain and moderate to heavy at times across eastern CT
into RI and eastern MA. Trough amplification also results in
the offshore wave intensifying, with surface winds over SNE
backing to the NNW, cooling surface temps into the mid and upper
30s. Furthermore, this combined with height falls will yield
column cooling and may result in rain briefly mixing with or
changing to snow before ending Friday morning. The NAM offers
the most amplified solution and most snow on the backside. Can`t
completely discount this outcome, but none of the other hi res
guidance supports it. Even the NAM limits subfreezing surface
temps to the northern Worcester Hills and Berks, thus any minor
snow accumulation would be confined to this area. Otherwise,
just some wet snow possible before ending. Storm total qpf will
range from 1-2 inches, highest amounts over eastern CT into RI
and eastern MA, where there is low risk of up to 3 inches.

Winds - light NNE Thu evening shift to the NW overnight and become
gusty as offshore wave intensifies. NW winds 15-25 mph overnight,
except up to 35 mph across Cape Cod and the Islands.

Temps - in the 40s during the early evening, fall into the mid and
upper 30s overnight as rain possibly ends as a brief period of
wet snow. Any subfreezing temps will be confined to the highest
elevations of Worcester county & the Berkshires. Thus, not
expecting much if any impact. Although, we will need to watch
later model trends.

Friday...

Models have trended slower with precip departure, as open/negative
tilt mid level trough evolves into a closed low just east of
Cape Cod. Thus, rain, possibly mixed with wet snow at times may
linger across eastern MA into the afternoon. Otherwise, dry
weather overspreads the region from west to east with possible
late day clearing. Surface cyclone may become a sub 980 mb low
late Fri as it approaches Nova Scotia. This may yield NW winds
20-30 mph with gusts possibly up to 50 mph. Hence, a wind
advisory may be needed Friday. Seasonable temps Friday with
highs in the upper 40s to lower 50s, but gusty NW winds will
make it feel quite a bit cooler.

&&

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

* Windy on Saturday with sunshine and seasonable temperatures

* Dry and slightly above normal temps through Monday

* Unsettled weather returns Tuesday and Wednesday with an
  opportunity for substantial precipitation

Friday night and Saturday

Deep 850 hPa low over The Gulf of Maine deepen and stalls in
response to upstream blocking. With a ridge building gin from the
west the pressure gradient tightens and a strong low-level jet
develops over southern New England under northwest flow. This will
support a period of gusty northwest winds over the region with 30 to
40+ mph wind gusts possible Friday evening through Saturday morning.
The gradient gradually relaxes into Saturday afternoon, but a well
mixed boundary layer will continue to support 20 to 30 mph gusts for
much of the day Saturday. Drier air mass should support sunny skies
for most of the day Saturday with near normal temperatures.

Sunday and Monday

Winds diminish by Sunday as a mid-level ridge and surface high
pressure builds over southern New England. This will support dry
weather and slightly above normal temperatures through Monday. For
reference, the average high/low temperatures for Boston this time of
year is around 50 and 35 degrees respectively. High/low temps on
these days are forecast to be slightly higher than those values.

Tuesday and Wednesday

Latest suite of model guidance continues to support the development
of a low-pressure system over The Midwest early next week. As this
system moves east/northeast during the middle of next week, southern
New England is likely to see another round of substantial
precipitation. Details with respect to precip amounts and timing are
very vague at this time, so for now just expect a period of
unsettled weather for the middle of next week.

&&

.AVIATION /13Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

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

12Z update...

Today...high confidence.

IFR/LIFR conditions today in widespread rain, moderate to heavy
at times. Light and variable winds trend to NNE across RI and
eastern MA, NNW across CT and western-central MA.

Tonight...high confidence on trends, lower on exact timing and
details.

At 00z, IFR/LIFR in rain, moderate to heavy at times. Overnight,
improving trends to MVFR/VFR across CT into western MA,
improving to IFR/MVFR elsewhere. Rain may mix with or change to
wet snow at times toward 12z Fri. NNE winds in the evening
become NW overnight and increase to 15-25 kt, gusting up to 35
kt Cape Cod and Islands.

Friday...high confidence on trends, lower on exact timing and
details.

At 12z, IFR/MVFR across eastern MA and RI in rain, possibly
mixed with wet snow at times before ending during the afternoon.
Across CT into western-central MA, MVFR/VFR in the morning in
lingering light rain/snow, ends and improves to VFR in the
afternoon along with dry weather. NW winds increase to 20-30 kt
with gusts up to 40 kt.

KBOS TAF...High confidence in trends, some uncertainty in exact
timing of details. Rain may briefly mix with some wet snow
09z-15z Fri before ending.

KBDL TAF...High confidence in trends, some uncertainty in exact
timing of details. Rain may briefly mix with some wet snow
06z-12z Fri before ending.

Outlook /Friday Night through Monday/...

Friday Night: VFR. Strong winds with areas of gusts up to
40 kt.

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

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

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.

245 AM update...

* NW Gales possible Friday/Fri night

Today...high forecast confidence.

Frontal boundary draped across the MA/RI waters, with light NNE
winds developing across the eastern waters and NNW over the western
waters. Periods of rain early this morning become more widespread
later this morning into the afternoon, then moderate to heavy at
times lowering vsby.

Tonight...high forecast confidence.

Light NNW-NNE winds during the evening become NNW all areas after
midnight and rapidly increase to 20-30 kt as offshore low
intensifies into a gale center from the Carolinas to western Georges
Bank by 12z Friday. Rain, heavy at times will limit vsby.

Friday...high forecast confidence.

Gale center moves from western Georges Bank to near Nova Scotia. NW
winds 20-30 kt gusting up to 40 kt possibly at times. Any morning
rain/snow moves offshore with dry weather and improved vsby for the
afternoon.

Outlook /Friday Night through Monday/...

Friday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 9 ft.

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

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

Sunday through Sunday Night: Winds less than 25 kt. Seas
locally approaching 5 ft.

Monday: Winds less than 25 kt. Slight chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch through late tonight for CTZ004.
MA...Flood Watch through late tonight for MAZ004>007-012>024-026.
RI...Flood Watch through late tonight for RIZ001>007.
MARINE...Gale Watch from Friday morning through Saturday morning for
     ANZ231>235-237-250-251-254>256.
     Small Craft Advisory until 8 AM EDT Friday for ANZ250.
     Small Craft Advisory until 8 PM EDT this evening for
     ANZ254>256.

&&

$$

SYNOPSIS...Nocera
NEAR TERM...Frank/Nocera
SHORT TERM...Nocera
LONG TERM...RM
AVIATION...Nocera/KS
MARINE...Nocera/KS


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