312
FXUS61 KBOX 232330
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
630 PM EST Sat Nov 23 2024

.SYNOPSIS...
Gusty NW winds tonight and Sunday with winds gradually
decreasing late Sunday afternoon. High pressure builds into the
region Monday with dry and seasonable conditions along with
diminishing winds. A frontal system passing to our northwest on
Tuesday brings another round of rain, then blustery, cooler and
dry weather returns Tuesday night and Wednesday. Monitoring
another storm system that could impact southern New England
Thanksgiving into Friday with rain and wintery precipitation.
Blustery and colder next Saturday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
630 PM update...

Last of the shower activity is moving offshore from the outer
Cape. Low pres moving into the Maritimes with strong pressure
gradient in place will result in gusty NW winds tonight. Dry
weather will prevail, but can`t rule out a spot shower over the
Berkshires as mid level shortwave approaches from the eastern
Lakes. Otherwise, sct-bkn strato-cu at times, especially over
higher terrain as low level moisture lingers. Forecast on
track.

Previous discussion...

Key Messages (Through Sun AM)

* Gusty NW winds continue tonight into Sunday, with the
  strongest gusts over the east coast/Cape and Islands.

Subsident flow will gradually dry conditions out this evening
resulting in gradual clearing of clouds from west to east. Cold
air advection will keep lapse rates steepened enough to keep the
boundary layer uncoupled this evening. Gusty NW winds persist
with a 35-45kt LLJ oriented across southern New England. 20-30
mph gusts persist across most areas. Higher gusts are more
likely along the east coast, especially the Cape/Islands with
gusts 40-45 mph possible for a period as the LLJ shifts eastward
overnight. Hi-res ensemble guidance highlights far east Cape
Cod/Nantucket and Cape Ann with higher probabilities (80%+) for
gusts > 40 mph. Immediate east coastal areas have more moderate
probabilities, but a period of higher gusts can`t be ruled out.
A Wind Advisory has been taken into consideration for the late
afternoon-evening timeframe. However, the potential for this
criteria or higher is lower probability and limited in coverage.
Decided not to go with the Advisory. It will be gusty
regardless, so make sure to tie down any loose objects.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Sunday:

Northwest flow aloft will promote dry conditions tomorrow with cool
air continuing to advect into the region. As a result, steeper lapse
rates persist allowing efficient mixing of higher magnitude winds
associated with the LLJ to the surface. In normal words, it will be
another windy day tomorrow with gusts generally 25-35 mph with a few
isolated higher gusts possible earlier in the day near the Cape.
High temperatures will range around normal in the upper 40s to
around 50.

The LLJ shifts offshore tomorrow evening resulting in gradually
decreasing winds. With lighter winds and mainly clear conditions,
tomorrow night will be more favored for better radiational cooling.
Temperatures drop into the the mid 20s to low 30s for most of the
interior. Low to mid 30s closer to the coastline and metro
areas.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Key Messages:

* Dry and seasonable Monday with diminishing wind

* A period of beneficial wetting rains late Mon night into Tue

* Cooler and blustery but dry weather Wed

* Monitoring a potential storm that may impact the region
  Thanksgiving Day into Fri. Confidence in the details is low but
  potential for wintery precip.

Monday:

High pres builds in from the west with a dry airmass which will
bring sunshine and diminishing wind. NW winds may be gusty to start
the day but slackening pressure gradient will result in diminishing
wind in the afternoon. Temps will be near seasonable or slightly
above normal with highs upper 40s and lower 50s.

Monday night and Tuesday:

Fairly robust shortwave which takes on negative tilt will rotate
through New Eng during Tue. Modest low level jet will advect 1"+
PWATs northward into SNE ahead of the frontal boundary. Strong
forcing for ascent accompanying the shortwave will act on deep
moisture plume to bring a period of widespread showers to SNE. It
appears the showers will begin in western New Eng late Mon night
before overspreading the rest of SNE during Tue. This system is a
quick mover so rain should be exiting from west to east during the
afternoon, and may even some partial clearing mid-late afternoon
developing, especially in the interior. Ensemble rainfall probs
suggest about 0.20-0.50" rainfall. Mild day as southerly flow ahead
of the front will result in temps reaching upper 50s near the south
coast, with upper 40s to lower 50s interior northern MA.

Tuesday night and Wednesday:

Shortwave exits Tue evening with cold front moving offshore. Decent
shot of cold advection will bring blustery and colder conditions Tue
night and Wed, but dry weather with clearing Tue night and mostly
sunny skies Wed. Highs will range mostly through the 40s Wed.

Thursday into Friday:

Global ensemble guidance shows a favorable pattern for storminess
with strong high latitude blocking and ridging just off the west
coast leading to deep trough developing across Gt Lakes. Complex
pattern with Pacific shortwave rounding the trough interacting with
northern stream energy dropping into the upper midwest. Still a
large degree in uncertainty as global ensembles show a very large
spread in potential storm tracks from off the coast to well inland
which will lead to very different outcomes. Still too early to focus
on any particular scenario so will continue to favor a probabilistic
approach. Potential exists for first appreciable snowfall for
portions of SNE with ECMWF, GEFS and CMC ensembles all favoring best
chance in the interior with lower probs near the coast where rain
may be more likely. This seems reasonable given location of west
coast ridge which may be further west than you`d like to see for an
I-95 snow event. But this is a day 5-6 forecast and additional
changes in the guidance is likely so multiple scenarios remain on
the table. Stay tuned.

Saturday:

The storm should have exited into the Maritimes by the weekend with
blustery and colder conditions, although mainly dry weather.

&&

.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
Forecast Confidence Levels:

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

00Z TAF Update:

Tonight: High confidence.

SCT-BKN VFR ceilings. Gusty NW winds with gusts 25-35 kt,
strongest higher elevations and east coastal MA to
Cape/Islands.

Sunday: High confidence.

VFR conditions. Gusty NW winds 25-35 kt continue into the
morning hours, although NW gusts should ease to around 20-25 kt
in the afternoon.

KBOS Terminal...Moderate confidence in TAF.

A few showers through 20z. MVFR conditions improve toward VFR
around 20z. Gusty NW winds 20-25 kts. In the 20-00z timeframe,
gusts may peak up to 35 kts at times. WNW/W winds overnight
generally with gusts 25-30 kts continuing Sunday.

KBDL Terminal...Moderate confidence in TAF.

Low end VFR to high MVFR cigs this afternoon behind the last of
rain showers. NW winds with gusts 20-25 kts, peaking around
25-35 kt, which continue into the evening. WNW/W winds Sunday
with gusts 25-30 kts.

Outlook /Monday through Thursday/...

Monday: VFR. Breezy.

Monday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.

Tuesday: MVFR/IFR conditions possible. Breezy. SHRA likely.

Tuesday Night through Wednesday Night: VFR. Breezy.

Thanksgiving Day: Chance RA, slight chance SN.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Tomorrow

* Gale Warning in Effect through Sunday morning

Area of low-pressure over The Gulf of Maine will support gale
force northwest wind gusts 25-35 kts tonight through the first
half of tomorrow. Gale force gusts should begin to wane Sunday
afternoon as low-pressure slowly exits east over The Canadian
Maritimes. Offshore flow will limit seas close to the coast to
the 4 to 5 foot range, but the outer marine zones will see
higher seas with significant wave heights in the 5 to 8 foot
range.

Outlook /Monday through Thursday/...

Monday: Winds less than 25 kt. Local rough seas.

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

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas locally approaching 5 ft. Rain showers.

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Areas of rough seas.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft.

Wednesday Night: Winds less than 25 kt. Areas of rough seas.

Thanksgiving Day: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Warning until 4 AM EST Sunday for ANZ230-236.
     Gale Warning until 1 PM EST Sunday for ANZ231>235-237-250-251-
     254>256.

&&

$$

SYNOPSIS...KJC/Mensch
NEAR TERM...KJC/Mensch
SHORT TERM...Mensch
LONG TERM...KJC
AVIATION...KJC/Mensch
MARINE...KJC/Mensch