Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 130642
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
242 AM EDT Wed Mar 13 2024

.SYNOPSIS...

Dry weather persists today and Thursday with unseasonably mild
temperatures...but sea breezes on the immediate coast will keep
it much cooler in those locations. A more unsettled weather
pattern develops Friday into the weekend, with rainy conditions
for Fri and again on Sunday. Temperatures trend above normal
through this weekend, with a cooling trend toward more
seasonable temperatures by early next week.

&&

.NEAR TERM /THROUGH TODAY/...

240 AM Update...

* Plenty of sunshine today with some clouds arriving in the afternoon
* Highs mainly upper 50s/lower 60s but cooler immediate coast

The closed upper level low east of the Canadian Maritimes will
continue to move further east and away from the region today. This
will result in rising height fields as a mid level warm front
approaches. We still expect plenty of sunshine today...but do expect
an increase in mid/high level cloudiness by late in the day. Low
risk for a few brief sprinkles by late afternoon/early evening...but
it is so dry in the low levels not worth including in the forecast.

850T warming to between +4C and +6C coupled with a relatively dry
airmass in pre-greenup should allow temps to overachieve a bit.
Thinking highs inland from the coast will be mainly in the upper 50s
to the lower 60s with perhaps even a few middle 60s in the lower CT
River Valley. Winds will be rather light too...so quite a
comfortable afternoon for mid March standards. Meanwhile...weak
pressure gradient will allow for sea breeze development along the
immediate coast. This should keep afternoon temps in the upper 40s
to the lower 50s in this region.


&&

.SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/...

Key Points...

* Light/Calm Winds tonight with lows mainly in the 30s
* Plenty of sun Thu with highs 60s to near 70...cooler coast

Details...

Tonight...

Some mid/high level cloudiness this evening in association with the
mid level warm front. Otherwise...expect at least partial clearing
overnight with a ridge of high pressure taking control. Light to
calm winds will allow for overnight low temps mainly in the
30s...but a few upper 20s are possible in the normally coldest
outlying locations.

Thursday...

Upper level ridge axis approaches from the west. This will set the
stage for a beautiful Thursday across most of the region. Plenty of
sunshine expected with 925T climbing to between +9C and +12C inland
from the coast. Thinking temps likely overachieve a bit in pre-
greenup with highs mainly in the 60s inland from the coast. In
fact...a few locations in the Lower CT River Valley may hit 70. Weak
gradient though will allow for sea breezes along much of the
immediate coast...which will hold highs in the 50s in most of those
locales.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Highlights:

* Dry weather on Thurs, although increased cloud cover late in
  the day. Above normal temps.

* Soggy, dreary Fri with rain, perhaps with embedded downpours
  at times, however not expecting rains to rise to level where
  flooding is expected. Cooler, though still above normal temps
  for Fri.

* Mix of clouds and sun but dry Sat.

* Another frontal system around Sun bringing rains to Southern
  New England to usher in cooler more seasonable temps by early
  next week.

Details:

The 500 mb pattern across CONUS turns into a split flow regime
as we move into the latter part of the week into the weekend,
with a pretty active northern stream and a closed low over the
western Four Corners region. Ahead of this split flow pattern is
a building ridge over the southeast US, which will help steer
initial low pressure over the central Plains into the OH Valley
and Northeast by later Thurs night into Fri. Thereafter northern
stream troughing then reasserts itself across most of the
northern tier of states, with unsettled weather then re-
developing around Sunday. Overall, it is an unsettled weather
pattern although no one specific storm looks to be particularly
impactful. Temps start above normal on Thursday, and while they
continue to run generally above normal, a gradual cooldown is
expected each day before trending closer to seasonable by late
weekend into early next week.

Thursday through Friday:

First part of Thurs looks dry, albeit with increasing cloud
cover through the day. In addition, areas near the coast to see
light onshore flow and comparatively cooler temps compared to
well inland. Above normal temps however with highs lower-mid 50s
for the eastern coastlines, with highs well into the 50s to
lower 60s.

However our weather pattern then turns more unsettled as we
move into Thurs night through Fri. A shortwave disturbance aloft
moving around the periphery of (and ultimately topping) the 500
mb ridge over the southeast CONUS will result in low pressure
moving in from the Gt Lakes region. This will spread increased
cloud cover along with an increase in rain chances late Thurs
night but primarily into Fri. With today`s ensembles showing the
southeast US midlevel ridge amplifying a bit more than earlier
solutions, the track of sfc low pressure and initial warm
frontal precip shield shifted northward into northern MA, VT and
NH; however flattening ridging should spread widespread rains
into Fri. There is a little bit of elevated instability that
could be realized with potential for embedded downpours,
although did note GEFS/EPS QPF probs reflect a moderate- high
chance for 24 hr rain over 0.5" and very low to low probs (5-
15%) of 24 hr rain over an inch. Rain looks to shift offshore
Fri evening before trending drier toward early Sat AM, although
with lingering/intermittent showers near the coasts.

Saturday:

Weak shortwave ridging aloft develops over the Northeast as the
Friday storm system moves offshore; this occurs well ahead of
deepening troughing taking shape over the Northern Plains/Upper
Midwest. Expecting more of a mix of sun and clouds on Sat,
albeit with cooler though still above normal temps in the mid
40s to the lower 50s. Clouds again redevelop later Sat evening
ahead of the next system developing for Sunday. Lows above
freezing in the middle to upper 30s.

Sunday into Monday:

GFS/ECMWF and its ensemble means show split flow becoming
increasingly dominated by stronger northern stream troughing,
with building midlevel heights over the West Coast. Low pressure
then looks to move in from the Gt Lakes region Sunday into
Sunday night, with increasing clouds and increasing chances for
rains. Still a bit of uncertainty on the timing and strength,
and those details will need to be better refined before delving
into specifics but this will likely be our next best chance for
rain after Fri. After this system exits on Monday, expect
temperatures trending cooler and closer to seasonable levels as
deep troughing aloft builds into the Northeast states.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...

Forecast Confidence Levels:

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

06z TAF Update...

Today...High Confidence.

VFR. Light NNW winds shifting to the SE by afternoon with a sea
breeze component developing along portions of the immediate
coast.

Tonight...High Confidence.

VFR. Calm/light winds.

Thursday...High Confidence.

Light NW winds across the interior with sea breezes developing
along the coast.

KBOS TAF...High confidence in TAF. ESE sea breeze develops by
15z/16z.

KBDL TAF...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR. Chance RA.

Friday: Mainly VFR, with areas MVFR possible. Breezy. RA
likely.

Friday Night: MVFR/IFR conditions possible. RA likely.

Saturday: Mainly VFR, with local IFR possible. Chance RA.

Saturday Night: Mainly VFR, with local MVFR possible.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Thursday...High Confidence.

Any lingering marginal 5 foot small craft seas across our eastern
waters will subside by daybreak. Otherwise...a weak pressure
gradient will keep winds/seas below small craft advisory thresholds
today through Thursday with good vsbys.

Outlook /Thursday Night through Sunday/...

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Chance of rain.

Friday: Winds less than 25 kt. Rain likely.

Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Rain likely.

Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain.

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

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Chance of rain.

&&

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

&&

$$

SYNOPSIS...Frank/Loconto
NEAR TERM...Frank
SHORT TERM...Frank
LONG TERM...Loconto
AVIATION...Frank/Loconto
MARINE...Frank/Loconto


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