835
FXUS61 KBOX 302335
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
735 PM EDT Wed Apr 30 2025

.SYNOPSIS...
Cold tonight with lows in the 30s due to clear skies and calm winds.
Pleasant spring weather continues tomorrow with high pressure
overhead. Friday will feature a period of early-day scattered
showers and possible thunderstorms, with another round later
Friday afternoon. Rainy conditions then continue into Saturday,
wettest during Saturday afternoon into the evening. Our weather
pattern then turns cooler with a period of onshore flow for
Sunday into early next week, but there is larger uncertainty on
if this period will feature generally dry weather or potentially
soggy conditions.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
High pressure moves in overhead tonight, allowing winds to become
calm and skies to remain clear. This will set up the night for very
efficient radiational cooling. Low temperatures across much of the
region will drop into the mid-30s, with below-freezing temps
possible in NW MA. With  dewpoints dropping into the 20s to possibly
teens overnight, thinking there wont be much frost on the ground.
Even with some frost/freeze zones becoming active again starting at
midnight tonight, held off on any frost advisories for now.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Thursday:

High pressure remains anchored over the region, allowing for another
gorgeous spring day. With strong sun angle and dry soil conditions,
decided to bump up high temperatures using the 75th to 90th
percentile NBM. High temperatures away from the coasts should reach
the low to mid-70s, with upper 70s possible in the CT river valley.
Local sea breezes will keep coastal communities in the upper 50s to
low 60s. With very dry mid-level air, dewpoints will be quite low
tomorrow, possibly in the low to mid-20s. Winds tomorrow remain
light, eventually turning southerly late in the day. This should
help alleviate fire weather concerns with the low dewpoints
tomorrow.

Thursday Night:

A weak shortwave begins to exit the Great Lakes with a warm front
out ahead. Shower chances start increasing late overnight Thursday
into Friday, but a dry slot working in from the south may end up
limiting rain reaching the ground. With WAA and cloudy conditions
overnight, lows stay mild compared to tonight, in the upper 40s to
low 50s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Key Messages:

* Early-day scattered showers/embedded t-storms Fri, with perhaps
  another round of showers and embedded thunderstorms in western
  New England Fri aftn.

* Rainy conditions in all areas Sat, especially Sat aftn to night,
  tapering off early Sun.

* Period of cooler onshore flow likely late weekend into early next
  week, but large uncertainty on if we see extended dry weather or a
  perhaps prolonged period of soggy weather.

Details:

Friday:

Scattered showers with a few rumbles of thunder may still be ongoing
early on Fri but will be moving offshore by mid-morning. Latest
guidance continues to show potential for scattered afternoon showers
and thunderstorms in interior western New England, associated with a
stronger belt of 700-500 mb SWly flow leading to effective shear
magnitudes around 40 kt and mid-level lapse rates around 6.5 C/km,
but rather modest sfc based instability. Better instability does
reside west into central and eastern NY so somewhat better potential
for stronger storms into NY, but may have to watch for some of this
activity to perhaps move over the Berkshires late in the day. Left
open chances for thunderstorms from Worcester west through sundown,
then trended PoPs into the slight to lower Chance range as frontal
boundary stalls over or near SNE. Didn`t make too many change to NBM
temps in the 70s, but there is room to lower temps some in later
guidance if cloud cover lingers for a while.

Saturday:

Saturday still looks to be a washout as the next wave of low
pressure moves ENE along the frontal boundary. Still are some timing
differences across the models, but there is loose consensus on
periods of rain developing in all areas by the early afternoon,
while slowly lurching eastward into Sat night before then trending
offshore by early Sun AM. Total QPF amts around a half to three
quarters of an inch, with potential for locally more in spots where
slow moving downpours develop in a rather anomalously elevated PWAT
airmass. Highs lower to mid 60s coastal areas to the lower to mid
70s inland given tempered diurnal heating and expectation of
abundant cloudiness. Lows upper 40s to mid 50s.

Sunday into Early Next Week:

Global ensembles coming into agreement on an amplified 500 mb omega
block pattern evolving across CONUS, with an anomalously strong
upper ridge over the northern Plains and a closed upper low located
somewhere over the northeastern portion of the US. Its location
ranges from offshore of the Northeast states to as far west as the
Ohio Valley/northern KY area. Narrowing down the location of this
upper level feature is critical in delineating possible effects on
our weather here. Though it appears a period of prolonged onshore
flow looks to develop with cooler temps near the coasts, current
possibilities range from strong ridging to our north and generally
dry weather with an enhanced onshore flow (GFS) or a period of
prolonged soggy conditions associated with a ribbon of deeper
moisture being advected northward around the periphery of the upper
low into interior SNE and the mid-Atlantic (ECMWF/GEM). While it`s
reasonable to expect cooler temps with a period of onshore flow,
that`s otherwise quite a range of outcomes that still need to be
ironed out. Offered below normal temps following NBM guidance with
chances for rain showers, with more detail to come once models come
into better agreement on a drier or wetter pattern.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

00z update...

No changes to 00z TAFs.

Tonight: High Confidence

VFR. Light northerly winds

Thursday: High Confidence

VFR.  Light and variable winds in the morning, turning light
southerly in the afternoon.  Local sea breezes develop between 13-14z

Thursday Night: Moderate Confidence

VFR to start, becoming MVFR late overnight as WAA kicks in.
Scattered light showers are possible late overnight.


KBOS TAF...High Confidence in TAF.

KBDL TAF...High Confidence in TAF.

Outlook /Friday through Monday/...

Friday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHRA, slight chance TSRA.

Friday Night: VFR. Breezy. Chance SHRA, isolated TSRA.

Saturday through Saturday Night: Mainly VFR, with areas MVFR
possible. SHRA likely, slight chance TSRA.

Sunday: VFR. Chance SHRA.

Sunday Night: VFR. Slight chance SHRA.

Monday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight and Thursday: High Confidence

Tranquil boating conditions through tomorrow with high-pressure
overhead. Winds remain light northerly tonight, turning light
southerly tomorrow. Seas decrease to 1-3 feet.

Thursday Night:

Increasing southerly winds, staying below 25 knots. Low chance
for showers and perhaps and rumble of thunder.

Outlook /Friday through Monday/...

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Slight chance of rain showers.

Friday Night through Saturday: Winds less than 25 kt. Seas up
to 5 ft. Chance of rain showers, slight chance of
thunderstorms.

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers, isolated thunderstorms.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 AM EDT Thursday for ANZ254>256.

&&

$$

SYNOPSIS...Loconto/KP
NEAR TERM...KP
SHORT TERM...KP
LONG TERM...Loconto
AVIATION...KJC/Loconto/KP
MARINE...Loconto/KP