BOX issues Area Forecast Discussion (AFD) at Oct 13, 8:38 PM EDT
166
FXUS61 KBOX 140038
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
838 PM EDT Tue Oct 13 2026
.WHAT HAS CHANGED...
Updated for the aviation section.
&&
.KEY MESSAGES...
- Showers through the evening, perhaps a rumble of
thunder.
- Mild and breezy day Wednesday. Low chance for an isolated shower
or sprinkle in the afternoon. Dry conditions Thursday with
seasonably cool temperatures.
- Low pressure system expected to bring rain Friday into early Saturday.
Gusty northwest winds and below normal temperatures expected
Saturday behind the system.
&&
.DISCUSSION...
KEY MESSAGE 1...Showers through the evening, perhaps a rumble of
thunder.
A fairly dynamic system, the bulk of which is passing by well to our
north, will be the forcing mechanism to bring the chance of showers,
and perhaps a brief rumble of thunder, to portions of the area late
this afternoon through late evening. Hi-res CAMs are not capturing
very well the cluster of stronger convection across parts of Ontario
into central New York, so confidence in the evolution and timing of
any showers that make it into southern New England is on the lower
side. The convection appears to be primarily elevated, and mid-
level lapse rates across our area are progged to be marginal to
maintain some of the activity. With no specific model doing well
with the current activity, I stuck with the blended guidance
approach, showing 30-40% PoPs in a general WNW to ESE orientation
from western MA down to SE MA and the Cape and points north of that.
Rainfall amounts should be generally 1/4" or less, though up to 1/2"
is possible, especially across far northern areas closer to the
VT/NH borders. Otherwise lots of low clouds, and some fog along the
coast courtesy of a moist low level southeast flow. As the evening
and overnight goes on, the winds will transition to southwest and
start to bring some drying to the low levels. So after any showers
move through, we should start to see partial clearing prior to
sunrise. On the flip side, those clouds will keep low temperatures
from dropping too much. In fact, some areas might see a slow rise in
temperatures.
KEY MESSAGE 2...Mild and breezy day Wednesday. Low chance for an
isolated shower or sprinkle in the afternoon. Dry conditions
Thursday with seasonably cool temperatures.
A trailing cold front shifts across the region Wednesday with
surface high pressure slowly building in from the west through the
day. This will gradually clear out the lower clouds through the
morning. Model soundings show sufficiently mixed supporting drier
conditions and breezy westerly winds. Gusts likely range between 20-
30 mph with a locally higher gust in the higher terrain of the
Berkshires. Westerly, downslope flow combined with 925mb
temperatures +16-18C will support a warm fall day with highs in the
70s in many areas. Isolate shower are possible as a weak wave moves
through in the afternoon, but this will be fairly limited in
coverage and more likely limited to a sprinkle due to the drier
lower levels.
As high pressure settles in further into Thursday, the airmass dries
out even more. Thursday will likely be dry, although cooler than
Wednesday. A cooler airmass will have moved in with 925mb
temperatures around 10C cooler than Wednesday. This will yield
seasonably cool temperatures mainly in the low 60s and lighter
northerly winds.
KEY MESSAGE 3...Low pressure system expected to bring rain
Friday into early Saturday. Gusty northwest winds and below
normal temperatures expected Saturday behind the system.
Deterministic and ensemble guidance show a deep northern stream
shortwave trough push across the Great Lakes and the northeast
Friday into Saturday. An upper level jet setting up near southern
New England will provide support for broad synoptic ascent and
advect a plume of anomalous moisture into the region. This will set
the stage for a widespread rain. Ensemble guidance ranges amounts
generally from 0.30 to 0.80". The ECMWF and Canadian still lean
wetter than the GFS despite its subtle upward trend in amounts. The
wetter solutions show potential for banded or localized amounts of
1.0-1.4", likely a result of the additional frontogenetical forcing
combined with marginal instability. Location of where the bands of
heavier amounts set up is still uncertain. Rain most likely arrives
in the Friday morning timeframe, continuing through the evening.
Most guidance shows this system to be fairly progressive meaning it
shifts out fairly quickly. The bulk of the rain likely exits late
Friday night with the pre-frontal trough. There is also an axis of
instability associated with this trough which may provide enough
forcing/support for a line of convective showers and perhaps even a
thunderstorm in the mix.
In addition, the initial southerly LLJ with this system nudges in
Friday which if mixed sufficiently, will bring breezy to gusty SW
winds. Gusts 20-35 mph are possible with potential for gusts up to
40 for the Cape and Islands and also Block Island.
A strong cold front pushes across the region by early Saturday
morning putting the northeast within a classic cold air advection
pattern with gusty NW winds, cooler temperatures, and isolated
showers. A NW 30-40 kt 850mb jet pushes into the region Saturday.
CAA will provide the steeper lapse rates to support deeper mixing
and thus gusty NW winds. The degree or mixing and strength of the
LLJ are still less certain this far out, but ensembles show a signal
for gusts 35-45 mph possible, potentially higher across the coastal
waters. 925mb temperatures range between -2C to +2C Saturday
yielding likely the coolest temperatures of the season so far. Highs
will likely struggle to get out of the 40s in most places. Some of
the higher elevation points across the Berkshires may struggle to
hit the 40 degree mark! RH fields show residual moisture within the
cyclonic flow pattern. This may be enough to support some isolated
showers. It's a bit too early to say the "S word" just yet(snow)
with confidence. However, if the timing aligns, a morning flurry
can't be ruled out in those highest terrain in the northern
Berkshires. No accumulation expected. Expect a cold night Saturday
night with high probabilities for non-coastal areas to be at or
below the freezing mark. Higher elevation locations may drop into
the mid-upper 20s.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00Z Update
Tonight...Moderate confidence (timing of ceiling improvements).
IFR to low end MVFR ceilings early tonight. Patchy LIFR in spots
like ORH. Ceilings are likely to gradually lift and break up as
low level winds start to transition more steadily to the SW
(after 06Z). Exact timing of improvements to VFR are lower
confidence with models showing improvement to VFR anywhere from
06Z to 15Z Wed morning. Showers through 03Z for more northeast
terminals (BED/BOS). Expect the best chances for showers to be
across MA, northern RI and across the Cape and points northward.
Probabilities for thunder are low (< 15%).
Wednesday...Moderate confidence (timing of ceiling improvements)
Lower confidence on exact timing of the improvements to VFR as
ceilings lift and scatter out early Wed morning. Most terminals
should be VFR by 15Z. W winds with gusts developing after 15Z
with gusts 20-25 kts. Can't rule out a g30kt for ORH. SCT decks
between 025-040 ft are possible through the day. It can't be
ruled out as a worst case that decks are high enough in coverage
to become a BKN MVFR deck in some areas across southern New
England. Gusts decrease after 21Z with winds shifting to the
WNW/NW.
Wednesday Night...High confidence.
VFR. NW winds 6-12 kts.
KBOS Terminal...Moderate confidence.
Showers through 03Z. Ceilings likely to hover between IFR and
low-end VFR tonight. The trend is for ceilings to gradually
improve/scatter out tonight into early Wed AM. The exact timing
is lower confidence. The most likely window is 09-13Z.
KBDL Terminal...Moderate confidence. Expect showers to remain
north of the airport this evening so did not include in the TAF,
however there is a 10-20% chance for -SHRA between 21-01z.
Outlook /Wednesday Night through Sunday/...
Thursday: VFR. Breezy.
Thursday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA.
Friday: MVFR/IFR conditions possible. Windy with gusts up to
35 kt. SHRA, slight chance TSRA.
Friday Night: Mainly VFR, with local IFR possible. Windy with
gusts up to 35 kt. Chance SHRA.
Saturday: VFR. Strong winds with local gusts up to 40 kt.
Saturday Night: VFR. Windy with local gusts up to 35 kt.
Sunday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Through Thursday...High confidence.
Winds turn SW early this evening as low pressure passes by to the
north. Expect to see winds increasing to 20-25kt away from the
coasts. Winds will turn more west/northwest for Wednesday, but still
continue in the 20-25kt range through mid-day. Winds start to
diminish later in the afternoon into evening. This will help to push
waves up to around 5-6ft, especially further offshore. Thus Small
Craft Advisories have been continued. Looking toward Thursday, winds
and seas will diminish as a ridge of high pressure moves across the
region.
Outlook /Wednesday Night through Sunday/...
Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft.
Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers.
Friday: Strong winds with gusts up to 35 kt. Areas of rough
seas. Rain showers, slight chance of thunderstorms.
Friday Night: gale force winds with gusts up to 40 kt. Rough
seas up to 13 ft. Rain showers likely.
Saturday: gale force winds with gusts up to 40 kt. Rough seas
up to 13 ft. Chance of rain showers.
Saturday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 12 ft.
Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from midnight tonight to noon EDT
Wednesday for ANZ231>235-237.
Small Craft Advisory until 2 AM EDT Wednesday for ANZ250.
Small Craft Advisory until 8 PM EDT Wednesday for ANZ254.
Small Craft Advisory from midnight tonight to 8 PM EDT
Wednesday for ANZ255-256.
&&
$$
DISCUSSION...Mensch/Nash
AVIATION...Mensch/Nash
MARINE...Mensch/Nash
Source: BOX issues Area Forecast Discussion (AFD) at Oct 13, 8:38 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202610140038-KBOX-FXUS61-AFDBOX)
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