National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS61 KBOX 231945
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
345 PM EDT Tue Apr 23 2024

.SYNOPSIS...
Wednesday brings scattered showers and a thunderstorm or two
as a cold front sweeps across the region. Very chilly Thursday
morning with a Freeze Watch in effect. More seasonable
conditions develop for the weekend. Another chance for showers
comes mid to late weekend.

&&

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

Dry and tranquil conditions persist this evening into much of the
overnight hours. Low pressure well to our south will continue to
filter some high clouds across southeastern MA and the Islands as
high clouds stream in from the west ahead of an approaching cold
front.

Winds from the south overnight advecting increased moisture over
southern New England, combined with increasing cloud cover will keep
temperatures considerable warmer than the last few nights, with lows
generally ranging from the upper 30s to low 40s. Rain showers
associated with aforementioned cold front may begin to push into
western MA and CT by daybreak, but expecting dry conditions through
the night for most.

Not expecting to decouple overnight in most locations which will
preclude any radiation fog formation, but winds may slacken just
enough by daybreak for some patchy advection fog to form across the
Cape and Islands.


&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...

Cold front sweeps across southern New England during the daylight
hours of tomorrow as trailing shortwave follows suit late afternoon/
early evening. Expecting two rounds of potential precipitation
tomorrow, the first between 12-18Z with katafrontal showers tapping
into SWterly flow enhanced PWATs, between 3/4 and 1". These showers
are not expected to bring significant precipitation to the region,
perhaps a tenth of an inch in any locality.

The second round of showers comes, at least as defined by the CAMs,
as a very "stubby" line of potentially convective showers initiate
by the trailing shortwave aloft between 18-23Z. CAMs remain varied
both in the position and geographic spread of these isolated to
scattered convective showers, but all 5 of the main HREF members
derive their existence tomorrow afternoon. Any convection will
remain elevated, and sub severe. Surface CAPE will be near zero as
cold air rushes in on W/NW flow, but breaks of sunshine during the
PM hours will allow a few hundred joules of MUCape to develop above
the surface inversion. All in all, expecting a few rumbles of
thunder, but confidence is rather low in who will see a passing
thundershower. At present, our best guess is somewhere in
central/eastern MA or in southeastern MA/RI as the shortwave pivots
east. Given the potential for convective showers, a few localized
rain totals in excess of 0.25" are possible.

Conditions clear very quickly after sunset across the area as winds
shift to the north overnight. Expected a very chilly night across
southern New England, but there are two scenarios as to how we may
achieve our morning lows. First, in a situation where we are unable
to decouple and radiate, anomolously cold air aloft, for late April,
with 925mb temps as cold as -5C, will partially mix to the surface,
which will derive lows in the mid 20s to low 30s region wide. The
second scenario, and perhaps the less likely scenario, is if we are
able to completely decouple overnight, which would yield radiating
under clear skies to dewpoints, which will be dismal in the mid 10s
to 20s. In reality, we may see somewhat of a mix of these solutions,
with the best chance for a period of slack winds across the far
interior of MA. Given uncertainty in the potential for radiational
cooling, utilize rather "middle of the road" guidance, the MAV,
depicting temperatures dropping to the low 20s in far NW MA and mid
to upper 20s outside of urban centers. Given the potential for
widespread temperatures in the mid 20s, we have hoisted a Freeze
Watch for portions of Connecticut, northern RI, and interior SE MA
where the frost/freeze program is now active. With that said, the
potential for a widespread freeze is stronger across the interior,
but because the frost/freeze program does not start in these
locations until May 1st, or later, based on the climatological last
freeze, there is no Freeze Watch in effect. Winds are expected to
stay high enough along the immediate coastline to preclude a hard
freeze. Will note, given the potential for a breeze overnight, this
is a likely a "freeze or nothing" scenario, with frost unable to
form given the winds.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...

Highlights

* Isolated to scattered showers on Thu, mainly across the interior,
  with slightly below normal temperatures.

* Dry for much of Fri with temps returning to seasonable levels.

* Cold front brings scattered showers late Fri through Sat. Mild
  temperatures return.

* The temperature roller coaster continues, with a return to near
  normal temperatures and dry weather for Sun into Tue.

Southern New England will be dealing with another mid level omega
block. This time through, we should initially be located beneath the
ridge portion of this block. Currently expecting this mid level
ridging to move off to our east towards this weekend, leading to a
transition to a broad mid level trough early next week.

At the surface, high pressure should remain in control of our
weather into Friday morning. Thus, mainly dry weather expected,
although there could be a risk for scattered showers towards its
edges, which would be mainly across the western half of southern New
England both Thursday and Friday. A slow moving front Saturday
should continue the risk for showers, before high pressure arrives
late this weekend into early next week.

Stayed close to the NationalBlend solution for this portion of the
forecast. Can see a scenario where rainfall chances could be lowered
in later forecasts for Thursday and Friday.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

Through tonight... High Confidence

VFR through 09Z Wednesday with MVFR cigs possible across
western terminals through 12Z. Rain showers develop ahead of
advancing cold front during the pre dawn hours and may creep
east into BAF/BDL prior to 12Z, but terminals farther east will
remain dry through the period. ESE/SE winds this afternoon
become south after 22Z. Winds shift further to the SW by
sunrise. Winds generally 10 to as high as 15kt, though some
gusts to 20kt possible along the south coast through sunset
tonight.

Wednesday...High confidence.

Generally low end VFR to MVFR, with lower cigs in showers
between 12-20Z. Localized IFR possible. Rain will trend showery
over stratiform in first surge of cold frontal precipitation.

A secondary round of widely scattered showers will develop after
20Z and may contain isolated TSRA. Uncertainty remains too high
to include a PROB30 or prevailing TSRA group at any terminal,
but the best chance for any sort of thunderstorm remains between
20-23Z.

Southwest winds shift to the west behind the frontal passage mid
day, winds gusting to as high as 20kt.

Wednesday night... High Confidence.

Rapid clearing expected from west to east, widespread VFR with
nearly clear skies. Winds shift to the north and will range
between 5 and 10kt.

KBOS TAF...High Confidence
Cold frontal passage brings showers
to the terminal between 10-20Z Wednesday. Low risk for TSRA
between 20-23Z before rapid clearing occurs. Winds ESE this
afternoon become SW overnight and W behind the frontal passage
tomorrow afternoon. Winds eventually become N by late Wednesday
night. Uncertainty in strength of winds on Wed night, but winds
will be greatest for coastal terminals, up to 25kt.


KBDL TAF...High Confidence
Cold frontal passage brings showers to the terminal between
10-20Z Wednesday. Winds become SW overnight and W behind the
frontal passage tomorrow afternoon. Winds eventually become N by
late Wednesday night.

Outlook /Thursday through Sunday/...

Thursday through Friday Night: VFR.

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night: Mainly VFR, with local IFR possible. Breezy.
Chance SHRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight...

Tranquil conditions persist for the waters with southeasterly
winds becoming more southwest overnight. Gusts to 25kt diminish
slightly overnight but resurges to around 20kt by early AM.

Wednesday and Wednesday night...

Cold front sweeps across the waters Wednesday afternoon bringing
showers and a wind shift from the SW to the W. Low chance for a
thunderstorm across the inner waters late Wednesday
afternoon/early evening but would be localized. Winds further
shift to the north overnight Wednesday, with gusts in excess of
25kt possible across the northeastern waters.

A small craft advisory is in effect for the outer and eastern
waters from 12Z Wednesday to 12Z Thursday for seas in excess of
5 feet and gusts in excess of 25kt.

Outlook /Thursday through Sunday/...

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

Thursday Night through Saturday: Winds less than 25 kt.

Saturday Night: Winds less than 25 kt. Slight chance of rain
showers.

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 20 kt. Areas of seas approaching 5 ft. Slight chance of rain
showers.

&&

.FIRE WEATHER...
Thursday...Potential Elevated Fire Weather Concerns.

Fire weather may again be a concern on Thursday depending on how
much rain falls on Wednesday, and how quickly winds subside as
high pressure builds in by Thursday mid-day. Further shifts will
need to evaluate this risk based on observations and model
guidance.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Freeze Watch from late Wednesday night through Thursday
     morning for CTZ002>004.
MA...Freeze Watch from late Wednesday night through Thursday
     morning for MAZ017-018.
RI...Freeze Watch from late Wednesday night through Thursday
     morning for RIZ001>004.
MARINE...Small Craft Advisory from 8 AM Wednesday to 8 AM EDT Thursday
     for ANZ231-250-251-254>256.

&&

$$

SYNOPSIS...Belk/KS
NEAR TERM...KS
SHORT TERM...KS
LONG TERM...Belk
AVIATION...KS
MARINE...Belk/KS
FIRE WEATHER...KS