BOX issues Area Forecast Discussion (AFD) at Nov 18, 6:54 PM EST971
FXUS61 KBOX 182354
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
654 PM EST Mon Nov 18 2024
.SYNOPSIS...
Dry and tranquil weather will continue through Wednesday
afternoon with cool nights and pleasant days. A developing low
pressure system will likely deliver much needed, widespread
meaningful rainfall Wednesday night and Thursday. Showers will
linger Thursday night and Friday with potential for some
accumulating snow over the highest elevations. Gradually drying
out next weekend and blustery.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
645 PM Update:
In terms of headlines for Tuesday...we've opted for a Red Flag
Warning for MA after partner feedback indicated active brushfire
activity today; while opting for a special weather statement for
CT and RI based on fire weather partner feedback in those
states.
Switching gears to current conditions...NW winds have begin to
lighten some across Southern New England, with current temps
still in the 50s for most, although some mid 40s are popping up
where winds are lightest. Most forecast models show at least
some NWly wind around for most of the night, and current look on
satellite imagery to our north indicating striations in the
stratocumulus cloud cover suggesting presence of a low-level
jet and CAA also lends credence to at least some NWly wind
tonight. Kept lows pretty close to unchanged, with only changes
with this update being to incorporate observed data and meshing
that into the forecast.
Previous discussion:
* Mostly clear with lows in the middle 30s-lower 40s tonight
The shortwave/cold front that crossed the region this morning will
continue to result in dry northwest flow aloft and at the surface
tonight. Cross sections indicate NW winds at 25 to 35 knots in the
925 mb layer. This should be enough to keep the boundary layer from
decoupling and temps from bottoming out in the typical low-lying
spots. Nonetheless...enough cool advection present to result in
overnight low temps bottoming out in the middle 30s to the lower
40s. Some 15 to 25 mph winds gusts will persist tonight
particularly across the typical non-decoupling spots.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Key Points...
* Mostly sunny Tue with highs 55-60
* Mostly clear/Diminishing Wind Tue night...Lows upper 20s/30s
Details...
Tuesday...
A ridge of high pressure will gradually nudge in from the west on
Tue. This should allow the pressure gradient to slowly weaken. We do
expect enough of a gradient for some 20-25 mph wind gusts especially
towards the I-95 corridor through mid afternoon...but these should
be on the downward trend by late afternoon. Good mixing and the very
dry airmass/ground should still allow Tue night temps to reach
between 55 and 60.
Tuesday night...
The ridge of high pressure continues to build further east into
our region. This will result in winds becoming calm/light with
mostly clear skies. So unlike tonight...we should see good
radiational cooling conditions. Overnight lows should bottom out
in the upper 20s/near 30 in the normally coldest outlying
locations...to the 30s in the urban centers.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Key Points...
* Dry with slightly above normal temps Wed
* Much needed widespread, meaningful rain late Wed night into Thu.
Showers lingering Thu night into Fri with potential for some
accumulating snow over the highest elevations in northern MA
* Still the risk of showers Sat, but gradually drying out through
the weekend with gusty winds
Details...
The main focus of the forecast comes on Wednesday night into
Thursday with the arrival of our first big precip maker in many
weeks. Before that, though, we'll have one more day of benign
weather under the influence of high pressure and mid level ridging.
Expect a good deal of sun with seasonable or slightly warmer than
seasonable high temperatures in the mid to upper 50s.
The pattern finally switches in the latter half of the week as a
sprawling upper low pressure center closes off over the Great Lakes
inducing cyclogenesis over the northeast U.S. including southern New
England. We'll see strong dynamics both at the low and mid level
with a 35-45 kt LLJ and 500 mb vorticity maxima swinging through New
England Wednesday night into Thursday. At the surface a secondary
low pressure forms over the Mid-Atlantic then strengthens directly
overhead providing convergence and low level orographic lift into
the slopes of the Berkshires. All this will work with a deep but
transient plume of moisture (PWATs approaching 1") between Wednesday
late evening to Thursday evening to produce widespread significant
rainfall on the order of 0.5 to 1.5 inches. The wettest locations
will likely be in places that are orographically favored with
upslope easterly flow like the Berkshires and Worcester Hills.
Secondarily there will be enough cold air aloft to support some snow
at the highest elevations of interior MA, mainly above 1,500 ft but
details on any potential accumulations won't come into focus for a
while. The best chance of snow comes on the back end Thursday night
into Friday as winds shift and colder air moves in. As this happens
the rain showers for the lower elevations become more scattered and
showery with the upper low sitting overhead into Saturday. Overall,
a windy and wet Thursday become less windy and less wet on Friday
then clearing out even moreso Saturday into the weekend as the low
finally lifts toward Nova Scotia. Temperatures for the weekend will
drop back to near average, with highs in the upper 40s/low 50s.
&&
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update:
Tonight: High confidence.
VFR. NW winds around 5-10 kt, although could see occasional
gusts to 20 kt this evening especially in eastern MA/RI.
Tuesday...High Confidence.
VFR. NW winds of 5 to 15 knots with some 20 to 25 knot wind
gusts at times into mid afternoon before diminishing.
Tuesday night...High Confidence.
VFR. Winds becoming Calm/Light with a continued NW direction.
KBOS Terminal...High Confidence in TAF.
KBDL Terminal...High Confidence in TAF.
Outlook /Wednesday through Saturday/...
Wednesday: VFR.
Wednesday Night: Mainly VFR, with local IFR possible. Breezy.
Chance RA.
Thursday: Mainly MVFR, with areas IFR possible. Breezy. RA.
Thursday Night: MVFR/IFR conditions possible. Breezy. RA
likely.
Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance
RA.
Friday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance RA.
Saturday: Mainly VFR, with areas MVFR possible. Breezy. Slight
chance RA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Tuesday night...High Confidence.
Modest northwest LLJ coupled will generate NW 25 knot wind gusts at
times tonight into mid afternoon Tue. Small craft headlines are
posted for most of the waters over this time...with the
strongest winds over the waters tonight and nearshore during the
daylight hours Tue. A ridge of high pressure building in from
the west should allow winds/seas to diminish below small craft
thresholds across most waters by late Tue afternoon. Winds
continue to diminish Tue night and no marine headlines will be
needed.
Outlook /Wednesday through Saturday/...
Wednesday: Winds less than 25 kt.
Wednesday Night: Winds less than 25 kt. Chance of rain.
Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Rain.
Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft. Rain likely.
Friday through Friday Night: Winds less than 25 kt. Areas of
rough seas. Rain likely.
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of rain.
&&
.FIRE WEATHER...
645 PM Update:
Tuesday...
In terms of headlines for Tuesday...we've opted for a Red Flag
Warning for MA after partner feedback indicated active brushfire
activity today; while opting for a special weather statement for
CT and RI based on fire weather partner feedback in those
states.
Northwest wind gusts of 15 to 25 mph are expected Tue with the
strongest of those gusts across eastern MA. Minimum afternoon RH
values are expected to drop to between 30 and 40 percent on Tue.
Wednesday...
High pressure building in from the west will result in much lighter
winds Wed...generally less than 10 mph. Minimum afternoon RH values
are expected to drop between 45 and 55 percent.
Thursday...
A much needed widespread 0.50 to 1"+ of rain is on tap for Thu. This
should result in significant easing of the current Fire Weather
concerns.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Red Flag Warning from 7 AM to 6 PM EST Tuesday for MAZ002>024-
026.
RI...None.
MARINE...Small Craft Advisory until 1 PM EST Tuesday for ANZ231>234-250-
251-254-255.
Small Craft Advisory until 1 PM EST Tuesday for ANZ235-237-256.
&&
$$
SYNOPSIS...Frank/BW
NEAR TERM...Frank/BW/Loconto
SHORT TERM...Frank
LONG TERM...BW
AVIATION...Frank/Loconto/BW
MARINE...Frank/Loconto/BW
FIRE WEATHER...Frank
Source:
BOX issues Area Forecast Discussion (AFD) at Nov 18, 6:54 PM EST----------------
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