251
FXUS61 KBOX 270518
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
118 AM EDT Fri Sep 27 2024

.SYNOPSIS...
Cold front brings rain this afternoon into tonight with a low
chance of thunder. Drying out on Friday as high pressure builds
in from the north and remains through Monday. The next chance of
rain showers comes toward the middle of next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
10 PM Update:

Stronger line of heavy showers have formed across the south
coast in response to roughly 100-250 J/kg of MUCAPE. Not
expecting any thunder with this line as reflectivity values
above -10C are well below 35dbz.


8 PM Update:

Current surface observations show a cold front dropping
southward across southern New England switching the winds north
behind it. Along with it, a couple batches of showers push
south and east across the region. This is a bit quicker than
originally anticipated, so made some minor adjustments to the
forecast to reflect this. Things will improve quicker as a
result. Still can`t rule out lingering showers across the south
coast and Cape early Friday morning.


Highlights:

* Cold front brings rain this afternoon into the first-half of the
  overnight.

* Low risk of an isolated thunderstorm.

Abundance of clouds and areas of rain continue this afternoon across
the region due to a cold front and a robust mid-level northern stem
shortwave. Keep the umbrella on standby if heading out this evening
as showers are expected to become more numerous and cannot rule
out a rumble or two of thunder. And honestly, the area with the
better chance of hearing any thunder are those near the
southern coast of RI and south coast of MA. There is VERY
limited instability, nearly zero units of SB CAPE, but 100-200
units of MUCAPE. This area also coincides where a weak fine
line could develop. Winds aloft are fairly robust, in this fine
line, could see stronger wind gusts of 30 to perhaps 40 mph,
sub-severe, but still notable. Otherwise, warm cloud layer is
around 12,000 feet, meaning the storms are good rain makers, a
few heavier downpours are possible this evening and given storm
motion around 20 to 25 knots, storms are expected to be moving
quickly and limits the flood threat.

Lows tonight are generally in the middle 50s, could hold on to 60
degrees in urban areas like Boston, Providence, and Hartford.

Given higher dewpoints overnight, patchy ground fog is possible, but
not likely to become dense.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Highlights:

* Cold front stalls south of southern New England. Generally a dry
  day with more in the way of sunshine north and clouds south.

* Near seasonable temperatures.

Today`s cold front stalls to the south of southern New England and
depending how far south it reaches will dictate how much sunshine
places like Hartford, Providence, and Taunton have. Current thoughts
are the front is stalled south of the islands. This should keep our
area fairly dry, but have left a mention of "Iso. Rain" in the grids
for areas south of the Mass Pike through 18z. North of the Mass Pike
have more in the way of sunshine with higher pressure building down
from the north. Somewhere, a tight gradient of clouds/no clouds will
develop, a shift 30-50 miles could lead to more sun all or more in
the way of clouds. Feel this will be the same story heading into the
overnight hours as well.

Did lean on a blend for tomorrow`s temperatures, afternoon highs in
the low to middle 70s. Warmest spots are in northern Massachusetts
due to higher likelihood of sunshine. Nighttime lows in the
50s, with the coolest spots north, less cloud cover, and warmest
south near 60F due to the higher cloud cover.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Points:

* Dry conditions prevail through early next week

* Next chance for rain arrives by mid-week

Details:

For the weekend, the previous upper level trough will be exited well
to the east with weak ridging building in across the northeast. This
will put southern New England under subsident NW flow aloft. This
will support dry conditions while remnant of Helene stays to the SW.
Surface high pressure positions to the northeast, bringing in
onshore flow. Moisture will range around normal and with cloudy
skies and breaks of sun. Temperatures range in the mid to upper 60s,
with low 70s further inland in the CT River Valley.

Weak upper level ridging prevails into early next week with an upper
level low slowly tracking toward the northeast. Monday will likely
remain dry with highs in the 60s to low 70s. Ensemble guidance is
highlighting differences in the timing of this system with some
members having it arriving by Tuesday and others by Wednesday. Based
on ensemble means, will more likely see showers/rain chances
increasing Tuesday afternoon into Wednesday. There`s a low chance
for an earlier onset of showers Monday night/early Tuesday. High
temperatures range in the mid 60s to near 70 in spots.

Ensemble guidance shows a transition to more zonal flow aloft toward
the end of the work-week next week with mainly dry conditions
favored.

&&

.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

Rest of tonight...Moderate Confidence

Rain continues to dissipate inland while a heavier band remains
over the Cape and Islands. That band should move off shore
before sunrise. Guidance is mixed on how quickly CIGS lift to
VFR with some guidance hinting at radiation fog developing with
all the residual moisture around from yesterdays rains.

Today...High confidence.

VFR with light northerly winds. Localized sea breezes develop near
the coasts.

Tonight...High Confidence.

VFR with light and variable winds. Patchy radiation fog
possible esspically in the northern CT river valley.

Saturday...High Confidence

VFR with east winds at 5-10 knots.

BOS TAF...Moderate Confidence in TAF.

VFR today with light NNW winds. Sea breeze should develop late
this morning to early this afternoon.

BDL TAF...Moderate Confidence in TAF.

VFR today with light northerly winds

Outlook /Saturday Night through Tuesday/...

Saturday through Monday Night: VFR.

Tuesday: VFR. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Friday Night...High confidence.

Showers and perhaps a rumble of thunder as a cold front moves across
the waters this afternoon through the overnight hours. Rough seas
and periods of stronger gusts, extended the Small Craft Advisory for
the outer ocean waters through tonight, seas ease heading into
Friday with improved conditions by Friday afternoon.

Outlook /Saturday Night through Tuesday/...

Saturday: Winds less than 25 kt.

Saturday Night through Sunday Night: Winds less than 25 kt.
Seas locally approaching 5 ft.

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

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ250-
     254.
     Small Craft Advisory until 2 AM EDT early this morning for
     ANZ251.
     Small Craft Advisory until 11 AM EDT this morning for ANZ255.
     Small Craft Advisory until 8 AM EDT this morning for ANZ256.

&&

$$

SYNOPSIS...Mensch
NEAR TERM...Dooley/Mensch/KP
SHORT TERM...Dooley
LONG TERM...Mensch
AVIATION...KP
MARINE...Dooley/Mensch