BOX issues Area Forecast Discussion (AFD) at Dec 29, 4:19 AM EST472
FXUS61 KBOX 290919
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
419 AM EST Sun Dec 29 2024
.SYNOPSIS...
Overcast with drizzle and areas of dense fog this morning, with
a period of light rain showers late this morning. Unseasonably
warm conditons and southerly breezes develop tonight, then a
cold front will bring windswept showers with brief downpours
Monday. Another low pressure system should bring rain New Years
Day. Then colder and drier weather should follow into the first
weekend of 2025.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
410 AM Update:
Key Messages:
* Foggy conditions will continue, locally dense at times.
Visibility improves by late morning to mid afternoon.
* Brief period of light rain showers mid morning to early
afternoon, then turning rather mild!
Much of Southern New England is socked in with stratus and areas
of dense fog early this morning with calm winds. There are many
sites with visbys at or less than a quarter mile, mainly away
from the southern coast, and BOS and BDL have been at or flirting
with categorical minimums. Dense Fog Advisory is in effect for
most of Southern New England through 12z Sunday; admittedly
visbys in RI and portions of southeast MA are borderline at
best, given proximity of diffuse frontal boundary lying through
Buzzards Bay and just enough of a SWly push of wind to improve
visbys. Guidance suggests visbys however may continue to drop
near the end of the current expiration of the Dense Fog
Advisory; for now, will let this Advisory stand with no changes
and then re- assess its status, which could include possible
extensions into the morning for some areas.
Improvement in visibilities may not take place until the
stalled boundary near our southern waters returns northward as a
warm front late this morning into the early afternoon, and
allows for an increase in wind speeds to around 5 mph. Passage
of this warm front will bring a period of light rain showers
(QPF amts less than a quarter inch) during the mid morning to
early afternoon hours, along with an increase in southerly winds
to around 5 mph, and a noticeable increase in dewpoints into
the mid 40s to low 50s.
Overcast/stratus is still expected after passage of the warm
front, with shallow moisture still locked in by the
strengthening thermal inversion. Could be some patchy fog around
too, but it should be far less widespread and visbys not nearly
as low as last night/overnight. So looking at an overcast warm
sector and temps rising through thermal advective processes.
Highs in the mid 40s to mid 50s today, coolest readings in the
Merrimack/CT Valleys.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
415 AM Update:
Tonight...
Continued overcast for tonight as warm advection and
strengthening southerly winds allows for steadily warming
temperatures through the night into the middle 50s! Fog is again
possible but the increasing winds will help keep visbys from
dropping, if it develops at all. That our light snowpack that
was once in place which has now been gobbled up by the rising
dewpoints is another factor that would mitigate fog development.
Monday...
Key Messages:
* Narrow band of windswept downpours moves through Southern New
England pre-dawn hrs to late-morning/noontime off the coast.
Flooding not anticipated.
* Southerly breezes to 25-35 mph, strongest Cape and Islands.
* Rapid clearing during the afternoon with peeks of sunshine
developing late-day.
The focus for more active weather comes from the approach of a
sharp cold frontal boundary/frontal occlusion toward the predawn
hrs, associated with a powerful low pressure area that is
forecast to move through the Gt Lakes late tonight and into
central Ontario on Monday. Height falls/diffluence aloft and
strong surface/low-level convergence will lead to the
development of a strongly- forced line of downpours (a "fine
line" / "squeegee line" of downpours we often see in strongly-
forced cold-season cyclones). Models and convective- permitting
ensemble output seem to be in fairly strong agreement in timing
this band moving through Southern New England during the pre-
dawn and late morning hrs (4-11 AM). Local downpours are
possible and phrased as "rain heavy at times" in the zone
forecast, with PoPs briefly into the Categorical range. Forecast
rain amounts are around one half to an inch, and though this
will all fall in a few hours' time during the Monday morning
commute, it is fairly progressive and shouldn't result in any
hydro issues.
Ahead of and just before the band of windswept downpours, strong
warm/moist advection through strengthening southerly low level
jet progged at around 60-70 kt at 925 mb. However the core of
this low-level jet is locked up in the warm-nose inversion. It
is notable that the 00z HREF ensemble minimum 10-m gust progs shows
a swath of southerly gusts of 40 mph near the southeast coast
during the mid morning hours before frontal passage. These
situations are always challenging in strong southerly low level
jets with the core of the jet locked in the inversion. The
inversion is so strong that gusts around 25-35 mph should be
more common, and there also isn't a strong isallobaric rise/fall
couplet which would tilt the scale toward a potential stronger
wind gust scenario.
Cold front moves offshore, and allows for moderately strong cool
advection. Monday will still be rather warm even post-frontal,
with highs in the mid to upper 50s, but at least the cold
advection aloft will allow for increased mixing and allow the
overcast to lift/disperse rapidly.
&&
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
410 AM update...
Key Messages
* Mild and sunny on Tuesday
* Another round of substantial rain Tuesday night through Wednesday
* Trending cooler and drier Thurdsay through next weekend
Tuesday
A mid-level ridge axis build in behind departing low pressure Monday
night into Tuesday. This will support a dry/sunny Tuesday afternoon
for most of southern New England with highs in the low to perhaps
mid 50s. The western areas may see increasing cloudiness during the
mid-afternoon hours as return flow from the south and associated
warm advection transport low-level moisture over the region. Overall
a mild/quiet day on Tuesday.
Tuesday night and Wednesday
Rain chances increase Tuesday night into Wednesday as a warm front
associated with low-pressure approaching from The Midwest lifts
through the region. This area of low pressure will move through the
region Wednesday morning into Wednesday afternoon bringing another
round of substantial rainfall to southern New England. Not expecting
any PType issues given the mild antecedent conditions, but can't
rule out a brief period of snow over the higher elevations of
western MA behind the associated cold front Wednesday evening.
Ensembles means for liquid equivalent precipitation are coming in
around 1 inch as of the latest model cycles.
Thursday through Next Weekend
High pressure and a cool/dry air mass settle in behind the departing
low-pressure system. This will bring temperatures back down closer
to normal for early January. The pattern looks to support dry
weather through at least the first half of next weekend. Stay tuned
for further details.
&&
.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z TAF Update:
Today...High confidence in flight categories, moderate
confidence in exact details
IFR/LIFR ceilings and vsbys persist today with light winds.
-SHRA develop with a lifting warm front in the afternoon. This
may support some improvements to vsbys, but ceilings likely
remain in the IFR/LIFR category.
Tonight...Moderate Confidence
Winds increase out of the south/southeast to 10 to 15 knots. IFR
ceilings persist with some improvements to MVFR over
southeastern MA and The Cape. Vsbys improve to MVFR as well.
Steady rain develops ater 06Z as an area of low pressure moves
over the region.
Tomorrow...High confidence in trends
Rain continues through mid-morning under IFR ceilings.
Improvements to VFR likely by late morning/early afternoon as
rain tapers off to the east. Modearte southerly winds from 10 to
20 knots with some gusts to 25+ knots.
KBOS TAF...Moderate confidence, especially with timing of
changes Sunday. Fairly confident visibility will stay aob 1/2SM
in fog through the morning push. No significant improvements
expected until Monday morning.
KBDL TAF...High Confidence
Outlook /Monday Night through Thursday/...
Monday Night: VFR. Breezy.
Tuesday: VFR.
Tuesday Night: MVFR/IFR conditions possible. Breezy. RA.
New Years Day: Mainly MVFR, with areas IFR possible. Breezy.
RA.
Wednesday Night: Mainly VFR, with local MVFR possible. Windy
with areas of gusts up to 30 kt. Chance RA, slight chance SN.
Thursday: VFR. Windy with gusts up to 30 kt.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High- greater than 60 percent.
415 AM update...
High confidence through tonight, then becomes moderate for
Monday.
Today...warm front slowly moves into RI/MA waters from south to
north. Winds remain light from the south. Periods of rain with
areas of dense fog reducing vsby to less than a mile at times,
especially in the morning.
Tonight...warm front lifts north into NH/ME waters, with
southerly winds increasing to 15-25 kt late. Drizzle in the
evening is replaced by heavy showers toward morning. Areas of
fog will limit vsby to 1-3 miles.
Monday...Continued the SCAs although latest guidance suggests
potential for a few gusts to 35 kt over the eastern waters
despite poor mixing. This is due to a stronger low-level
jetstreak. Later shifts will need to eval for a possible
upgrade to Gale. Windswept rains may reduce visby to 3 SM during
the late morning to early afternoon, then winds shift to SW and
decrease late.
Outlook /Monday Night through Thursday/...
Monday Night: Winds less than 25 kt. Rough seas up to 9 ft.
Tuesday: Winds less than 25 kt. Local rough seas.
Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain.
New Years Day: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 9 ft. Rain likely.
Wednesday Night: Strong winds with gusts up to 35 kt. Rough
seas up to 10 ft. Chance of rain.
Thursday: Strong winds with gusts up to 35 kt. Rough seas up to
10 ft. Slight chance of rain.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Dense Fog Advisory until 7 AM EST this morning for CTZ002>004.
MA...Dense Fog Advisory until 7 AM EST this morning for MAZ002>022-
026.
RI...Dense Fog Advisory until 7 AM EST this morning for RIZ001>007.
MARINE...Small Craft Advisory from midnight tonight to 4 PM EST Monday
for ANZ230-231-250-251-254.
Small Craft Advisory from 9 PM this evening to 1 PM EST Monday
for ANZ232>237-255-256.
&&
$$
SYNOPSIS...Loconto
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...RM
AVIATION...Loconto/RM
MARINE...Loconto/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Dec 29, 4:19 AM EST----------------
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