BOX issues Area Forecast Discussion (AFD) at Oct 8, 7:40 PM EDT115
FXUS61 KBOX 082340
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
740 PM EDT Tue Oct 8 2024
.SYNOPSIS...
Dry and seasonable weather conditions are expected tonight into
Wednesday. A dry cold front moves through Southern New England
Wednesday night, which will bring increasing northwest breezes
and cooler than normal temperatures for Thursday. Temperatures
moderate Friday, and especially Saturday, when highs may reach
into the 70s, before cooling off again Sunday and Monday. Mainly
dry weather lasts through Saturday, though rain chances
increase to close out this holiday weekend.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
Rather quiet weather continues this evening. Areas of mid and
high level clouds were skirting the south coast of New England,
with mainly clear skies elsewhere across southern New England
with the loss of daytime heating. Monitoring another band of
mid level across NY state that should arrive later tonight,
then be offshore by morning. Not expecting much frost tonight
because of these clouds. Airmass is rather dry, so not expecting
showers to develop until the weak lift is able to tap into the
ocean for additional moisture.
Brought temperatures back in line with observed trends and tried
to account fro the clouds alter tonight.
145 PM Update:
Really nice Fall day underway across Southern New England with
abundant sun from the Berkshires to the coastal beaches. This is
being supplied by a large surface ridge of high pressure over
the Gt Lakes into the central Appalachians and the mid-Atlantic
states. Aloft, much of the Northeast is governed by a rather
pronounced longwave trough. There are two shortwave
disturbances embedded in that longwave trough, one of which is
working its way through northeast MI at this hour and will move
through Southern New England later tonight. Ahead of this
initial weak shortwave trough is an enhancement to lower to mid-
level cloud cover seen in satellite imagery working its way
through central PA.
So for late this afternoon into tonight, mostly clear skies
will initially be in place with winds easing and shifting to
W/WSW. With that will be an increase in what should be mid to
high cloud cover per BUFKIT RH profiles. While some models
generate some light QPF with passage of approaching shearing-out
shortwave, subcloud layer looks dry enough that much of it will
evaporate before reaching the ground or produce a few sprinkles
at absolute worst, and a better if still a lower chance is over
southeast coastal New England. In other words, not impactful,
and the vast majority of Southern New England is dry. Passage
of this wave will bring decreased cloudiness and a windshift
from WSW to W/WNW by daybreak.
The forecast challenge for tonight is on temperatures. Should
see good radiational cooling for at least the first part of the
night; the issue is if the increasing mid to high cloud cover
will be enough to stall the cooling rate and/or cause early-
overnight low temps with a slow rise into the early Wed AM
period. I leaned closer to continuity on the cooler end of
guidance, but it could need some upward adjustments if cloud
cover trends toward a mid level overcast. Lows mainly in the
40s, with upper 40s/near 50 for the eastern coast and the urban
areas.
&&
.SHORT TERM /WEDNESDAY NIGHT/...
145 PM Update:
Wednesday:
Decreasing cloudiness early Wed gives way to full sun, albeit
with a broader cyclonic flow aloft and a cold pool aloft.
Looking at another day of mostly sunny conditions, although
diurnal cumulus should increase in coverage especially later in
the day. A second and stronger shortwave trough now rotating
around Hudson Bay is progged to move into northern New England
late in the day; so cloud cover should increase by later in the
day. Seasonable high temps with readings in the low to mid 60s,
thus another really nice day on tap for Wed.
Wednesday Night:
Winds shift to SW again Wed night, as a stronger shortwave
trough works its way through Southern New England. Despite the
strength of the trough, limited moisture should again keep much of
the area dry. Though there is a better chance Wed night sees
overcast conditions, the passage of the trough will usher in a
shot of stronger cold advection (e.g. 925 mb temps drop to
+2C, and 1000-500 mb thicknesses drop below 540 dm). It will
also bring increased NW breezes upon its passage. The clouds and
the increased winds will keep temps in the upper 30s to low-mid
40s. If temps were to drop into the mid 30s/around the level
at which frost would develop, the winds would be too strong to
mitigate its development.
&&
.LONG TERM /THURSDAY THROUGH TUESDAY/...
Key Points:
* Temperatures around normal this week, except for possibly
Saturday
* Dry weather pattern likely prevails into this weekend. Next
chance for precipitation potentially arriving by late Sunday
into Monday.
Details:
Relatively good overall synoptic agreement for this portion of
the forecast period. There are some timing differences, which
is not all that unusual. In the broad view, mid level cutoff
over SE Canada should be pushed out over the Maritimes towards
Friday. This leaves behind a rather flat flow across the
northern tier of the USA. This is where some of the timing
difference of shortwaves start to creep into the forecast. Much
will depend on the influence of a deep mid level low near the
Aleutians, and how that amplifies the downstream longwave
pattern this weekend into early next week. Our region is
expected to remain on the cooler side of this flow.
At the surface, high pressure should move from over the Great
Lakes Thursday to the central Appalachians for Friday. This
will keep whatever is left of Milton well to our south, and well
offshore of the southern New England coastal waters. A
moisture-starved cold front should arrive late Saturday as this
high pressure moves farther south.
This leads to our next chance for showers as a low pressure
arrives in the Great Lakes, then moves into the Saint Lawrence
River valley some time late this weekend into early next week.
This timing is subject to change with later forecasts.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Through Wednesday Night: High confidence.
VFR through this forecast period all terminals. Will have a
period of enhanced mid level cloud cover tonight with passage
of one shortwave disturbance, and again for late Wed and Wed
night with a stronger shortwave trough, but no rain is expected.
Winds become SW under 10 kt tonight. Winds then trend WNW by
daybreak around 10 kt. For Wednesday, westerly winds around
10 kt most of the day, though will become NW and increase to
around 10-15 kt with gusts around 18-20 kt late Wed night/early
Thurs AM.
KBOS TAF...High confidence in TAF. VFR. W under 10 kt. Winds
then turn to NW toward pre-dawn hrs Wed with passage of a dry
shortwave trough.
KBDL TAF...High confidence in TAF. VFR. Calm winds becoming light
W/NW late tonight.
Outlook /Thursday through Sunday/...
Thursday through Saturday: VFR. Breezy.
Saturday Night: VFR.
Sunday: VFR. Slight chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Wednesday Night: High confidence.
SCA will continue over the eastern outer water into early Wed
morning due to continued 4-6 ft seas, although the trends are
down.
W/NW winds around 10-15 kt through Wednesday. NW wind gusts
increase Wed evening/early Thurs AM to around 20 kt and could
approach SCA level but probably falls just short of criterion.
Seas will decrease on the outer waters to 4ft or less by early
Wed, but remain at that level through Wed night.
Outlook /Thursday through Sunday/...
Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.
Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.
Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 20 kt. Seas up to 5 ft.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.
Sunday: Winds less than 25 kt. Slight chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Wednesday for ANZ250.
Small Craft Advisory until 1 PM EDT Wednesday for ANZ254-255.
&&
$$
SYNOPSIS...Belk/Loconto
NEAR TERM...Belk/Loconto
SHORT TERM...Loconto
LONG TERM...Belk
AVIATION...Belk/Loconto
MARINE...Belk/Loconto
Source:
BOX issues Area Forecast Discussion (AFD) at Oct 8, 7:40 PM EDT----------------
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