Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 222010
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
410 PM EDT Fri Mar 22 2024

.SYNOPSIS...
Active period of weather arrives late tonight through Saturday
night with heavy rain, flooding, wintry weather, and marine
hazards. Drying out Sunday into early next week but rather windy
along the coast, especially Cape and Islands. Below normal
temperatures will prevail. The next chance of rain will be
Wednesday and Thursday as another frontal system approaches.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Tonight/early tomorrow

First half of the night is quiet across the region with some
increasing cloud cover and light winds ahead of a robust low-
pressure system that will move over the region tomorrow. Active
weather begins to settle over southern New England during the early
morning hours as a surface warm front associated with a deepening
low-pressure system begins to lift over the region. Temperatures on
the north side of the warm frontal boundary will be well below
freezing. As warmer air aloft overruns the cooler air in place,
we`ll begin to see precipitation develop in the form of light snow
showers across western MA and CT. As the warm nose edges further
north, a melting layer develops between about 850 and 900 hPa. With
surface temps remaining at or below freezing, this will support a
freezing rain profile for north/northwest Hartford county, western
MA, and northern Worcester county. Based on latest suite of ensemble
guidance, freezing rain may begin as early as 5am  across western
MA/CT and continue through 09 to 10 am when surface temps will begin
to rise above freezing and allow a changeover to rain. Prior to the
changeover, substantial ice accumulations from a few hundredths of
an inch to a tenth of an inch or more will be possible. For this
reason, a winter weather advisory remains in effect for the
aforementioned areas expected to experience freezing rain. Winds
increasing out of the southeast to 10 to 15 knots during this period
as well.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Tomorrow

By mid-morning tomorrow, surface temps will have increased to above
freezing across southern New England. This will result in any
remaining frozen precipitation changing over to rain. From there on
out, the rest of tomorrow is a complete wash out. A coastal low
develops and moves off the mid-Atlantic coast before tracking over
or just southeast of The Cape/Islands. An impressive region of
frontogenesis develops across southern New England by early
afternoon and will support a period of heavy rainfall that may
result in urban, small stream, or poor drainage flooding. Latest
HREF run paints a swath of 2 to 4 inches of rain across CT, RI, and
southeastern MA with the heaviest rainfall between roughly 2pm and
8pm. While confidence in a significant rainfall event is higher than
normal, even subtle changes in the storm track could result in the
axis of heaviest rainfall lifting north or south, so there still
remains a bit of uncertainty at 24 hours out. Given the relatively
wide goal post for the axis of heaviest rainfall, a flood watch is
in effect for the southern and eastern forecast areas. Only northern
Worcester county, Franklin, and Hampshire counties are excluded. In
addition to small stream flooding, some larger area rivers in
southern RI are at risk for flooding as well (see Hydro AFD
section). Temperatures range from upper 30s to low 40s across the
interior/northwest areas tomorrow, with more mild temperatures in
the upper 40s to low 50s across southeastern MA and RI.

Tomorrow Night

Surface cold front associated with the low-pressure system moving
over southern New England pushes through the region tomorrow
evening. This brings precipitation to and end for most of the region
from west to east between about 8pm and 2am. Clearing and strong
northwest winds from 15 to 25 mph will follow the cold front. Precip
lasts a bit longer over The Cape/Islands tapering off between
roughly midnight and 4 am. Temps dive into the low to mid 20s across
the interior/northwest areas and upper 20s to low 30s across
southeastern MA/RI prior to sunrise on Sunday.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Highlights:

* Mostly dry Sun into Tue, but blustery with below normal
  temperatures. Quite windy over the Cape/Islands

* Increasing risk of wet weather Wed into next Fri. Temperatures
  trending back above normal late next week.

A broad mid level trough is expected to morph into a mid level
cutoff over the North Atlantic early next week. This should trap the
surface low pressure beneath it, and keep it lingering offshore of
southern New England. Still some uncertainty in just how far
offshore this low pressure will wind up being. At present, thinking
the latest NationalBlend (NBM) deterministic solution is on the
pessimistic side of the envelope. Maintained a faster departure of
clouds and rainfall Sunday.

High pressure over eastern Canada is expected to nudge into our
region for Monday and Tuesday, leading to mainly dry and partly
cloudy conditions across most of our region. The exception to that
will be across far eastern MA, and especially the Cape and islands.
Thinking clouds may linger longer there, along with a few showers
Sunday morning. Will possibly need a Wind Advisory at some point
Sunday into Sunday night into Monday. It`s marginal still, so not
very high confidence. With all the other ongoing headlines, will
wait until confidence increases before issuing such a headline.

The weak high pressure should maintain dry weather MOnday and
Tuesday, but also bring in colder air with a persistent N to NE
wind. Eventually though, this high pressure should break down and
move farther offshore. That will open the door for a slow-moving
front to impact southern New England late next week, most likely
some time from late Wednesday into Friday. It should not be a total
washout, but looking at the prospect of a prolonged period of
unsettled weather. Will need to monitor the impact of any additional
rainfall on our creeks, streams and rivers, which should still be
recovering from the rainfall this weekend.

Temperatures should trend warmer mid week, and likely return to
above normal temperatures Thursday into Friday.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

18Z update...

Through 00Z... High Confidence

VFR. Increasing mid-high clouds from 080-120. Steady 5 to 10
know westerly winds weakening and becoming light southwest by
00Z.

Tonight...High confidence in trends. Moderate in timing.

VFR through about 06Z with light southwesterly winds becoming
more south/southeasterly. Conditions begin to deteriorate after
06Z as precip associated with a surface warm front lifting over
southern New England begins to support MVFR ceilings and light
precip. Frozen precip will be an issue at the western terminals
(BDL/BAF/ORH). A brief period of -SN followed by -FZRA will be
possible beginning as early as 08Z. Elsewhere, any precip will
be limited to -RA, but likely will be closer to or after 12Z
before precip reaches the eastern terminals.

Tomorrow...High confidence in trends. Moderate in timing.

-FZRA pay persist at BDL/BAF/ORH through as late as 14Z, but
 will changeover to rain thereafter with surface temps rising
 above freezing after sunrise. MVFR cigs/vsbys deteriorate to
 IFR by 18Z as rain overspreads the region. Rain picks up in
 intensity after 18Z and remains steady through 00Z. Southeast
 winds gradually increase throughout the day ranging from 10
 knots across the interior to 15 to 20 knots over the coastal
 plain.

Tomorrow Night... High  trends. Moderate in timing.

IFR/MVFR cigs improve to VFR returns as precip gradually ends
from west to east from 00 to 06Z. Rain lingers a bit longer over
The Cape/Island terminals likely tapering off between 06 and
09Z with VFR returning to this area between 09 and 12Z. Winds
strengthen after 00Z behind a surface cold front. 15 to 25 knot
sustained northwest winds with gusts up to 35 knots.

Outlook /Sunday through Wednesday/...

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

Sunday Night through Monday: VFR. Strong winds with gusts up to
45 kt.

Monday Night: Mainly VFR, with local MVFR possible. Strong
winds with areas of gusts up to 45 kt.

Tuesday: Mainly VFR, with areas MVFR possible. Windy with gusts
up to 35 kt.

Tuesday Night: Mainly VFR, with areas IFR possible. Windy with
local gusts up to 30 kt. Chance SHRA.

Wednesday: MVFR/IFR conditions possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight

Quiet marine conditions through about midnight tonight. Thereafter,
winds begin to increase out of the southeast ahead of robust low
pressure system with sustained winds of 20 knots and gusts up to 25
knots by sunrise.

Tomorrow

Conditions deteriorate rapidly tomorrow as a strong low-pressure
system moves over southern New England. Steady 20 knot southeast
winds persist with gusts up to 35 knots possible, especially over
the southern Marine Zones. Seas gradually increase from 4 feet early
in the day to 6 to 9 feet by tomorrow evening. Near-shore eastern
zones stay a bit lower with 4 to 6 foot seas. A gale watch is in
effect through Monday morning.

Tomorrow Night

A cold front moves over the waters tomorrow night. 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 marine zones and 6 to 10
feet for the near-shore zones.

Outlook /Sunday through Wednesday/...

Sunday: Moderate risk for gale force winds with local gusts up
to 45 kt. Rough seas up to 15 ft.

Sunday Night through Monday: gale force winds with gusts up to
45 kt. Rough seas up to 15 ft. Slight chance of rain showers.

Monday Night: Moderate risk for gale force winds with gusts up
to 45 kt. Rough seas up to 15 ft.

Tuesday: Low risk for gale force winds with gusts up to 35 kt.
Rough seas up to 13 ft.

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 10 ft. Slight chance
of rain showers.

Wednesday: Winds less than 25 kt. Areas of rough seas. Chance
of rain showers.

&&

.HYDROLOGY...

Heavy rainfall tomorrow afternoon and tomorrow evening is likely
to lead to minor and perhaps moderate river flooding in
southern Rhode Island. Greatest risk for minor flooding appears
to be along the Wood River at Hope Valley where the MMEFS
indicates a 94 percent chance of minor flood stage being reached
and a 54 percent chance of moderate flood stage being reached.

Several other rivers across southern New England including the
Shawsheen, Charles, Assabet, Pawcatuck, and Pawtuxet rivers are
at an elevated risk to reach at least minor flood stage due to
excessive rainfall.

The Pawtuxet River at Cranston is of particular concern given
latest ensemble forecast guidance paints a bullseye of 2 to 4
inches of rain over this basin in only a 3 to 6 hour time
period. MMEFS indicates a 63 percent chance of moderate flood
stage being reached and even a 24 percent chance of major flood
stage being reached. Residents and businesses near this location
will want to keep a close eye on updates for potential river
flood warnings and take action accordingly.

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 2 AM to noon EDT Saturday for
     CTZ002.
     Flood Watch from Saturday morning through Sunday morning for
     CTZ002>004.
MA...Winter Weather Advisory from 2 AM to noon EDT Saturday for
     MAZ002>004-008>011-026.
     Flood Watch from Saturday morning through Sunday morning for
     MAZ005>007-009-011>024.
RI...Flood Watch from Saturday morning through Sunday morning for
     RIZ001>008.
MARINE...Gale Watch from Saturday afternoon through Monday morning for
     ANZ230>237-250-251-254>256.

&&

$$

SYNOPSIS...Belk/RM
NEAR TERM...RM
SHORT TERM...RM
LONG TERM...Belk
AVIATION...Belk/RM
MARINE...Belk/Dooley
HYDROLOGY...RM


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