BOX issues Area Forecast Discussion (AFD) at Sep 6, 11:00 AM EDT
627
FXUS61 KBOX 061500
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
1100 AM EDT Fri Sep 6 2024
.SYNOPSIS...
A ridge of high pressure across New England will result in dry
and seasonably warm conditions today into Saturday, but an
approaching cold front will bring a period of showers late
Saturday into Saturday night. Meanwhile, low pressure moving
northward over the Atlantic will bring increasing surf and rip
currents on east-facing ocean beaches of eastern MA later today
and especially Saturday. Cooler and drier weather follows
Sunday, then high pressure will bring dry weather for much of
next week with a warming trend. Temperatures will be near to
slightly warmer than seasonable through the week, but with a
few cool nights.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
11 AM Update...
Forecast is on track for the most part and no major updates were
needed to the previous forecast. Day Cloud Phase satellite
imagery shows the stratus deck gradually scattering out with a
good portion of improvement from SE to NW. Overall, this is a
a little slower than previously anticipated. Nothing crazy
impact-wise except for slightly cooler temperatures than
forecast for most spots. Highs will still range in the 70s
today.
720 AM Update...
Forecast generally on track, but did make some adjustments to
increase sky cover due to stratus coverage per latest obs. In
addition, added a bit more fog due to current obs. The
fog/stratus should gradually lift/scatter this AM. Though may be
a bit slower across eastern areas due to prolonged E to NE flow.
Rest of forecast looked okay at this point, but if clouds linger
a bit longer than anticipated then temps may need to be lowered
in future updates.
Previous discussion...
Ocean storm lifts north over the Atlantic and passes well east of
the Benchmark this afternoon. Subsidence and ridging across New Eng
between this offshore system and upper trough moving into the Gt
Lakes will result in dry conditions today. Developing stratus and
patchy fog will impact the morning and there is a low risk for some
patchy drizzle. However, increasing mixing with low level moisture
becoming more shallow will result in lifting cloud bases and
sunshine developing in the afternoon. Seasonably warm temps with
highs upper 70s to near 80, but cooler along the eastern MA coast
with E-NE flow. Humidity will be increasing as dewpoints climb into
the 60s. It will become a bit breezy over Cape and Islands with
gusts 20-25 mph this afternoon/evening as the low pres passes to the
east.
It is worth noting, NHC does give this subtropical low a 30% chance
of development over the next 48 hours. But not expecting any impacts
other than increasing surf and dangerous rip currents developing,
especially over Nantucket, Block Island and outer Cape then
expanding to rest of exposed eastern MA coastline tonight and
Saturday.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tonight...
SNE will remain in between offshore low pres and approaching upper
trough from the Gt Lakes. Surface ridging and subsidence will lead
to dry conditions, but stratus expected to redevelop during the
night from east to west. Showers assocd with offshore low pres
passing well to the east will remain east of New Eng tonight. Lows
will range from mid 50s to near 60. Gusty NE-N winds in the evening
across Cape/Islands.
Saturday...
The offshore low pres will move into the Maritimes by late in the
day as robust upper trough moves east from the Gt Lakes. Hi-res and
global guidance has come into better agreement on timing of the cold
front moving into western New Eng late in the day. Consensus of the
guidance has trended faster with deepening moisture plume and
showers moving into western MA/CT during mid-late afternoon, but
much of eastern New Eng should remain dry. Overall, expecting partly
sunny skies after any stratus burns off with clouds increasing in
the west during the afternoon. Highs should reach mid-upper 70s,
warmest in eastern MA.
High surf conditions and risk for dangerous rip currents will peak on
Saturday along the exposed eastern MA coastline as easterly swell
builds to 6-8 ft just offshore. We expanded the High Surf Advisory
to eastern MA coast.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights
* Cold front quickly bringing showers through Saturday Night.
* Dry with near to slightly warmer than normal temperatures Sunday
through essentially the whole week. Strong radiational cooling
will lead to some cool nights.
Saturday Night...
A deep cutoff/trough will be located over the eastern Great
Lakes/Ontario and Quebec Fri evening. A shortwave rotating around
the cutoff lifts into New England during the evening and through
northern New England by early Sun as the cutoff lifts into Quebec. A
cold front quickly moves through during this timeframe. High
pressure begins to nudge in by early Sun.
Only opportunity for showers for the foreseeable future in the
extended. Guidance has come in better agreement with the fronts
progression through the area, so have adjusted PoPs to fall more in
line with this as the NBM was too broad/slow. Best chance for
showers comes during the evening and showers quickly exiting after
midnight. Only concern here is all guidance showing that we dry slot
per 700 hPa RH. This tends to erode precip quicker than forecast
from past experience.
Given the progressive nature of the front not anticipating heavy
rainfall with totals Sat Night generally around 0.10 inches or less.
There some instability with MUCAPES of a few hundred J/kg across
portions of the south coast. For now have kept thunder out of the
forecast given moisture quickly eroding with that dry slot pushing
in, but cannot completely rule out a few rumbles of thunder. Low
temps in the 50s across RI/eastern MA and in the 40s to low 50s
elsewhere.
Sunday through Thursday...
Cyclonic flow in place Sun through much of Mon as the deep cutoff
continues to lift northward across Quebec, Newfoundland and
Labrador. A ridge over the Northern Plains will build into the Upper
Mississippi River Valley by late Mon. The ridge builds into the
Great Lakes region for the rest of the week. High pressure nudges in
from the Mid Mississippi/Ohio River Valley on Sun/Mon and more
overhead or nearby for the rest of the week.
Dry and quiet weather anticipated with high pressure dominating.
Only change made was to lower overnight lows toward the 25th
percentile of guidance as am anticipating strong radiational
cooling. This should lead to a few cool nights with the coolest
readings Sun Night into early Mon with readings in the 40s for much
of the region. For the rest of the week lows generally falling into
the 50s as west/west-southwest flow aloft brings in some milder air.
Should rebound nicely during the day with temps gradually moderating
to slightly warmer than normal values as the week progresses.
&&
.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Today...High confidence in trends, moderate in timing.
Starting off with MVFR to LIFR conditions due to stratus. Should
gradually lift to VFR by late this AM/early afternoon, but could
linger across eastern areas due to prolonged onshore flow
(though may be right around MVFR levels and SCT out). Only
exception is across the Cape/ACK where VFR conditions prevail
through the day. Winds out of the E to NE at 5-10 kts.
Tonight...Moderate confidence.
MVFR to LIFR stratus redeveloping from E to W. Light N wind
interior, NE wind becoming N 10-15 kt Cape/Islands.
Saturday...Moderate confidence.
MVFR-IFR improving to VFR by midday, but showers and lower cigs
moving into western MA/CT late in the day. N wind becoming S
8-15 kt in the afternoon.
KBOS TAF...High confidence in trends. Lower confidence in exact
timing.
IFR/MVFR to start, but will gradually lift/scatter out to VFR by
16-18Z. Though wonder if ceilings still lingering around
borderline MVFR limits this afternoon with the prolonged onshore
winds. Will have a return of MVFR/IFR stratus tonight 03-06Z.
KBDL TAF...Moderate confidence.
IFR to start due to stratus, but will gradually improve to
MVFR/VFR later this morning and scatter out. The MVFR/IFR
stratus returns again late tonight, roughly 03-06Z.
Outlook /Saturday Night through Tuesday/...
Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA.
Sunday: VFR. Breezy.
Sunday Night: VFR.
Monday: VFR. Breezy.
Monday Night through Tuesday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Saturday...High confidence.
As offshore low pres passes east of the waters, NE winds will
increase to 20-25 kt over waters south and east of Cape Cod this
afternoon into this evening while winds gradually back to a more
north direction tonight. N winds 10-20 kt over eastern MA waters
tonight diminishing Saturday and eventually shifting to S-SW during
the afternoon. Seas building to 5-6 ft over outer southern waters
today, and 6-8 ft over eastern MA waters tonight and Saturday as
easterly swell increases from departing offshore storm. SCA remains
in effect for outer waters, and expanded it to the RI coastal waters
for seas this afternoon and evening, and for Nantucket Sound for a
period of 25 kt gusts.
Outlook /Saturday Night through Tuesday/...
Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Sunday Night through Monday: Winds less than 25 kt. Seas
locally approaching 5 ft.
Monday Night through Tuesday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents through Saturday morning for MAZ007-019.
High Surf Advisory from 8 AM to 8 PM EDT Saturday for MAZ007-
019.
High Risk for Rip Currents through Saturday evening for MAZ015-016-
020-021-023.
High Surf Advisory until 8 PM EDT Saturday for MAZ022-024.
RI...High Risk for Rip Currents through Saturday evening for RIZ006>008.
MARINE...Small Craft Advisory from 2 PM this afternoon to 10 PM EDT
this evening for ANZ232.
Small Craft Advisory from 2 PM this afternoon to 2 AM EDT
Saturday for ANZ235-237.
Small Craft Advisory from 4 PM this afternoon to 8 PM EDT
Saturday for ANZ250.
Small Craft Advisory from 2 AM to 8 PM EDT Saturday for ANZ251.
Small Craft Advisory until 8 PM EDT Saturday for ANZ254>256.
&&
$$
SYNOPSIS...KJC/BL
NEAR TERM...KJC/BL/Mensch
SHORT TERM...KJC
LONG TERM...BL
AVIATION...KJC/BL
MARINE...KJC/BL
Source: BOX issues Area Forecast Discussion (AFD) at Sep 6, 11:00 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202409061500-KBOX-FXUS61-AFDBOX)
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