-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBOX 231731
AFDBOX

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

.SYNOPSIS...
Chilly this morning, then turning comfortable and mostly sunny
this afternoon. Cold front moves across southern New England on
Wednesday with showers and perhaps isolated thunderstorms. Large
high pressure will build into the region Thursday through
Saturday bringing dry weather with moderating temperatures
Friday and Saturday. The next chance of showers will be Saturday
night into Sunday as a frontal system approaches. Much warmer
temperatures are possible by Sunday/Monday but a backdoor front
may keep much of the region cooler after all.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
9AM Update...

Pesky, but impactful, area of fog that draped over the southern
I-95 corridor from Providence to Boston this morning has fully
dissipated as of this writing thanks to daytime heating. This
area of fog formed along a well defined dewpoint boundary, where
dews were as much as 10F lower just north and west of the fog
compared to right along the boundary, where dews were observed
in the mid 30s to low 40s.

For the rest of the day, expecting abundant sunshine with
temperatures warming to near and above normal.

Previous update...

Highlights:

* Clear and chilly to start. Sunny and comfortable this afternoon.

Brr, a chilly start to the day thanks to clear sky cover overnight
and calm winds. Frost Advisory remains in effect until 7am due to
morning temperatures across portions of Connecticut and southeast
Massachusetts, as well as Rhode Island. Temperatures will quickly
climb into the low and middle 60s this afternoon, while the
immediate coast remains in the upper 50s. Plenty of sunshine this
afternoon due to a broad area of high pressure stretching across
much of the eastern seaboard.

Due to the dry profile of the lower atmosphere could have issues
with our dewpoint forecast today, did opt to use the the
percentile of the NBM, but this might not be low enough -
something the day shift will need to monitor. As it stands, the
minimum value of relative humidity this afternoon is 20 to 30
percent. Winds are from the south this afternoon at 10 to 15 mph
and gusts to 25 mph.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Highlights:

* Less cold Tuesday night, showers return for Wednesday and perhaps
  an isolated thunderstorm during the afternoon.

Overnight into Wednesday morning is less cold, due to the increasing
cloud cover and steady southerly wind, temperatures only drop back
into the upper 30s and low 40s. No threat for frost, but that does
return Wednesday night - likely to result in a new frost headline.

Our next chance for rain and perhaps an isolated thunderstorm is
Wednesday with the passage of a cold front and its associated robust
mid-level shortwave/trough. There is adequate moisture, PWATs are
between 0.7 and 1.0 inches, and lift to support numerous showers
during Wednesday morning. Do think the better chance for any rumbles
of thunder would be during the afternoon do the the steep mid-level
lapse rates - in addition to a couple hundred units of surface based
CAPE. QPF is in the neighborhood of 0.10 to 0.15 inch, but isolated
areas of higher amounts are possible within these isolated
thunderstorms.

Afternoon highs will depend a bit on the amount of clearing we have
during the afternoon, but generally a seasonable temperatures in the
upper 50s to low 60s. Behind the front, the wind becomes northwest
and sets the stage for a much colder night ahead.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Points...

* Widespread showers Wed and possibly an isolated t-storm, then
  drying and cold Wed night with freezing temps.

* Dry Thu through Sat. Cool Thu then milder Fri-Sat

* Chance of showers Sat night and Sun

Details...

Dry, post frontal NW flow kicks in late Wednesday and persists into
Thursday as high pressure expands from the Great Lakes into New
England. This will lead to a colder airmass once again overspreading
the region and lows in the upper 20s/low 30s Thursday morning.
Frost/Freeze headlines will likely be needed on Thursday and
potentially Friday mornings. The surface high remains in control
through Saturday, becoming centered over New England on Friday and
sinking to our southeast by Saturday night. This pattern offers
plenty of sun and light winds each day, so while relative humidities
will be quite dry on Thursday (20-30%) fire conditions shouldn`t be
too elevated unless the high is slower to advance east (and breezy
winds were to then linger into Thursday afternoon).

Our next chance of rain comes in the second half of the weekend as
the high pressure is shunted southward by our next shortwave
rounding the ridge. However, confidence is low for this portion of
the forecast given the wide range of possible scenarios. For what
it`s worth, both the EPS and GEFS ensemble guidance have at least a
30% chance of measurable rain by Sunday afternoon, so odds of
unsettled weather will be on the rise regardless. The biggest
forecast challenge will be for high temperatures Sunday and Monday.
Guidance continues to advertise the chance for the warmest temps of
the season so far (well into the 70s). However, the possibility of a
backdoor cold front to keep much of our region colder looms large;
this would result in a large gradient from eastern MA to southwest
CT. GEFS ensemble guidance is less enthused with the widespread
warmth than the EPS at this point. Stay tuned.

&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
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 /Wednesday Night through Saturday/...

Thursday through Friday Night: VFR.

Saturday: VFR. Breezy.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Wednesday...High confidence.

Tranquil early season boating conditions due to a broad area of high
pressure across the eastern seaboard. A cold front moves across the
waters Wednesday, bringing showers and the potential for isolated
thunderstorms during the second-half of the day. This period
features seas and winds below advisory criteria, but behind the cold
front Wednesday night, gusty northwest winds may result in marginal
small craft conditions.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

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

Thursday Night through Saturday: Winds less than 25 kt.

&&

.FIRE WEATHER...
Today...Elevated Fire Weather Concerns.

Minimum values of relative humidity this afternoon are forecast
between 20 and 30 percent this afternoon along with gusts up to
20 MPH. Due to pre-greenup conditions and a dry atmosphere there
are elevated fire weather concerns this afternoon.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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