-- Discussion containing changed information from previous version are highlighted. --
912
FXUS61 KBOX 230520
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
120 AM EDT Mon Sep 23 2024

.SYNOPSIS...

Weak high pressure will build over the region Monday and
Tuesday, but continued onshore winds should keep cloudiness over
southern New England, especially near the coast. Rain chances
increase again late Wednesday into Thursday as a frontal system
moves into the region. Warming trend with drier conditions
expected by next weekend.

&&

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

945 PM Update...

* Dry overnight with lows mainly in the upper 40s & 50s

A ridge of high pressure nosing down from the northern New
England/Canadian Maritimes will combined with the distant ocean
storm and allow for considerable cloudiness overnight.
However...enough low level dry air coming in from the northeast
to keep the weather dry overnight. Low temps will range from
the 50s on the coastal plain with some middle to upper 40s
across portions of the interior.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...

Monday...

Weak trough aloft moves east across New Eng but surface ridging and
wedge of drier air will maintain dry conditions. However, expect
more cloud cover as strato-cu will be prevalent across the region
given the extent of low level moisture in place, along with high
clouds moving from the west. Highs will in the mid-upper 60s, and
around 70 in the CT valley. Gusty NE winds will continue over
Cape/Islands from persistent pressure gradient between offshore low
pres and high pres to the north.

Monday night...

Forecast persistence as surface ridging remains in place across New
Eng with weak mid level ridging moving in from the west. Expect dry
conditions with varying amounts of cloud cover. Lows mid-upper 40s
interior and low-mid 50s near the coast.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Highlights...

* Onshore flow will yield clouds and seasonably cool conditions
  Tuesday and Wednesday.

* Frontal system sometime mid to late week brings another chance for
  rain

* Warming and drying trend develops for the weekend

Surface backdoor cold front draped across southern New England will
dominate the weather pattern through Wednesday morning with onshore
surface flow yielding cloudy and seasonably cool conditions with
patchy drizzle at times; especially along the immediate coastline.
Substantial precip is not expected with surface high pressure
centered about upstate NY/southern Ontario. This continued onshore
flow will likely lead to the High Surf Advisory being extended
through Tuesday, though the coastal flooding threat continues to
diminish now that the Full moon has passed.

A shift in the pattern of persistence is not expected until the
second half of Wednesday into Thursday as a mid level low/trough
shifts south over New England and high pressure moves to our east.
This trough will bring a period of unsettled weather in the
Wednesday night to Thursday timeframe, but as mentioned by the
previous forecaster, there remains uncertainty in how quickly
showers develop, which may lead to a primarily dry day Wednesday
with more widespread rain developing during the overnight and early
Thursday period. Shower activity may continue into the first half of
Friday, particularly across the eastern half of our CWA. In terms of
total QPF, not expecting a blockbuster event with ensemble
probabilities of 0.5" of rain in the ballpark of 30-50%; highest
north of the MA Turnpike. Chances of an inch of rain in 24 hours,
ending 06Z Friday, peak around 20%.

Mid level low drifts to our southeast by the weekend with at least
an attempt at mid level ridge development across the Ohio River
Valley expected late Saturday into Sunday. After several days of
clouds, anticipating an improvement to a mix of sun and clouds by
the weekend before strong ridging develops early next week. Also
expect temperatures to warm gradually through the end of the week
and into next weekend back towards seasonable, in the upper 60s to
mid 70s by Friday/Saturday.

&&

.AVIATION /05Z MONDAY THROUGH FRIDAY/...

-- Changed Discussion --
Forecast Confidence Levels:

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

06z TAF Update...

Today...High Confidence.

A broken deck of mainly VFR with some pockets of marginal MVFR
ceilings. The lower conditions are most likely towards the
coastal plain and during the morning hours after sunrise. ENE
winds of 5 to 15 knots with some 20+ knots across the Cape and
up to 25 knots towards Nantucket.

Tonight...High Confidence.

VFR to MVFR broken ceilings are on tap for tonight. The
scattered MVFR ceilings are most likely during the late night
and overnight hours and towards the coastal plain with the
cooling boundary layer. NE winds generally less than 10 knots.

Tuesday...High Confidence.

A broken deck of VFR to MVFR ceilings will tend more towards
VFR during the afternoon. ENE winds of 5 to 15 knots.

BOS TAF...High Confidence in TAF. Greatest risk for a period of
MVFR ceilings will be this morning through about 16z and then
again very late tonight.

BDL TAF... High Confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Mainly VFR, with areas MVFR possible.

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

Wednesday Night through Thursday: Mainly VFR, with local IFR
possible. Chance SHRA.

Thursday Night: VFR. Slight chance SHRA.

Friday: Mainly VFR, with local MVFR possible.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Forecaster Confidence Levels:

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

Overall high confidence through Monday night. SCA headlines will
continue for all waters except Boston Harbor and Narragansett Bay
for a combination of wind and seas.

Offshore low pres combined with high pres to the north will maintain
gusty NE winds with gusts to 25 kt, especially over SE waters. These
winds should begin to diminish Mon night as pressure gradient begins
to relax. Seas will be rough, 8-10 ft over the outer waters
through Monday, then slowly subsiding to 6-8 ft Mon night.

Outlook /Tuesday Night through Friday/...

Tuesday: Winds less than 25 kt. Rough seas up to 8 ft.

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

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

Thursday: Winds less than 25 kt. Local rough seas. Chance of
rain showers.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers.

Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.
-- End Changed Discussion --

&&

.TIDES/COASTAL FLOODING...
Total water level at Boston has peaked at 12.7 ft so some minor
inundation issues likely along exposed east and NE facing beaches.
Astronomical tides are about 0.5 ft less Monday afternoon so with a
similar surge we are not expecting any flooding concerns during the
Mon afternoon high tide.

High Surf Advisory extended through Monday due to high seas and
rough surf.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...High Surf Advisory until 8 PM EDT this evening for MAZ007-019-
     020-022>024.
RI...High Surf Advisory until 8 PM EDT this evening for RIZ006>008.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ231>235-237.
     Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-251-
     254>256.
-- End Changed Discussion --

&&

$$

SYNOPSIS...KJC/KS
NEAR TERM...Frank
SHORT TERM...KJC
LONG TERM...KS
AVIATION...Frank/KS
MARINE...KJC/KS
TIDES/COASTAL FLOODING...KJC