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000
FXUS61 KBOX 222036
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
436 PM EDT Mon Oct 22 2018

.SYNOPSIS...
High pressure will bring dry and unseasonably chilly weather
tonight. Low pressure will bring a few showers to the region on
Tuesday, particularly across northern Massachusetts where a
period of steadier showers are possible. Some showers linger
into Wednesday as low pressure pushes across the Canadian
Maritimes. High pressure moves across through late this week,
bringing the coldest air of the season late this week lingering
into early next weekend. Strong low pressure may work up the
eastern seaboard, with rain possible this weekend and a mix of
snow possible at the onset inland.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Southwest winds have brought in more clouds this afternoon with
some mid level moisture into SNE, but plenty of sun to be had
for most under partly sunny skies. Temperatures have climbed
into the upper 40s in the interior; more like low 50s along the
coast with generally light winds. This comes courtesy of the
area of high pressure currently centered to our south and the
mid level ridge centered over New England. This all moves off to
the east overnight ahead of a low pressure system and shortwave
trough dropping down from the Great Lakes region on Tuesday.
Ahead of that system tonight winds will be light with partly
cloudy skies, allowing good cooling into the mid 30s (quite a
bit warmer than we saw last night given the WAA). Early Tuesday
morning we`ll see our first shower chances over the Cape and
islands ahead of the incoming shortwave, but the majority of
the region won`t see rain until after sunrise.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Low pressure and the mid level shortwave approach from the
northwest bringing increased moisture, instability, and a
tightening pressure gradient. Precipitable waters will be on
the increase, as will cloud cover early Tuesday morning and
throughout the day; PWATs increasing to 0.5 to 0.75". A weak
warm front moves north during the day, though some hi-res
guidance has it stalling out along the MA/CT border, so that
will be something to watch with the temperature forecast. For
now going with temps warmer than today, in the upper 40s/low 50s
to the north and the upper 50s to near 60 along the south
coast. Given the front, moisture, and mid level instability from
our 500 mb cold pool aloft showers are expected to expand
through the morning after the initial round for the southeast
coast. No huge rain totals expected, generally a few tenths of
an inch. Pressure gradients will tighten as the low passes over
the region, and a 850 mb LLJ of ~35 kts passes just to our
south. Given potential for mixing we could see gusts of 30-35
mph over our south and east waters with 20-30 mph gusts over the
Cape and islands.

Tuesday night the low moves off the coast and we`ll be under
northwest winds with decreases rain chances. Winds will calm a
bit as well the jet moves off shore. Temperatures will be
several degrees warmer than the previous night, in the 40s
(upper 30s for higher elevations).

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

Overview...
Noting a highly amplified mid level steering pattern across
North America and beyond through most of the week into next
weekend. Large high pressure builds E across the northeast U.S.
late this week. This will bring a rather cold airmass across,
with H925 temps dropping to -3C to -6C by early Friday morning,
running up to around 3 SD (10-15 degrees) below seasonal
normals, though not quite to record levels for late October.

12Z medium range model suite continues to signal the potential
for a strong nor`easter remains in the forecast for the upcoming
weekend. However, this is still high uncertainty of how this
system will evolve, its ultimate track, and its impacts on the
region.

Details...

Wednesday...
Cutoff H5 low across northern New England moves slowly E,
taking its associated surface low with it. NW wind flow in
place, which will start to bring colder air across the region.
May see leftover isolated showers linger across central and
eastern areas, with the best chance across Cape Cod and the
islands through early afternoon.

Thursday through Friday...
Dry conditions as large high pressure crosses the region. Very
cold airmass builds SE out of the Arctic Circle across Hudson
Bay into the region on the backside of exiting cutoff H5 low
pressure. Expect highs both Thu and Fri in the 40s, with some
readings possibly holding in the upper 30s across the E slopes
of the Berkshires on Thu. Will also see NW winds on Thu, which
will produce wind chill values in the upper 20s to upper 30s.

Friday night through Sunday...
Strong low develops across the southern stream and, with
another digging H5 long wave trough across the Ohio Valley into
the interior SE U.S., models continue to push a strong surface
low off the SC/GA coast late Friday. Still a high amount of
uncertainty in how this low will track up the eastern seaboard,
how fast it will push up the coast, and how strong this low will
be. Models have quite a spread amongst their solutions at this
time, will continue to monitor closely.

Could see the precip onset in the form of snow across the
interior late Fri night or Sat morning, which could cause
problems especially with leaves on the trees. Another concern
may be with how strong the onshore winds may be, which may
bring a storm surge with it. Boston`s high tides will be around
11 feet this weekend, which could bring some storm surge if the
easterly winds are strong enough. Will monitor this potential
closely.

Monday...
Again, quite high uncertainty with the exit of this low, and
whether another surface system tries to wrap around digging
cutoff H5 low and trough out of the western Great Lakes. Have
kept low chance POPs for now, though temps will moderate some
so, at this point, less chance for mixed precip/snow. Still
quite a bit of time to watch this system.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

Through this afternoon...High confidence. VFR conditions
continue with W-SW winds 5 to 10 kts, some locations gusting to
20 mph.

Tonight...High confidence.
Generally remaining VFR, with potential for MVFR cigs under SHRA
over KHYA, KFMH, and KACK after 05Z. Spotty SHRA possible over
the rest of the region toward 12Z.

Tuesday...Low to moderate confidence.
Uncertainty remains with regards to northward extend of a warm
front. Best chance for MVFR/IFR under scattered showers
continues to be over northern MA. Shower chances decrease after
around 21Z.

KBOS Terminal...High confidence in TAF through tonight.

KBDL Terminal...High confidence in TAF through tonight.

Outlook /Wednesday through Saturday/...

Wednesday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.

Wednesday Night: VFR. Windy with local gusts to 30 kt.

Thursday through Friday: VFR. Breezy.

Friday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance SN.

Saturday: Mainly MVFR, with local IFR possible. Windy with
gusts to 35 kt. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

Tonight...High confidence.
A weak pressure gradient will keep winds/seas below small craft
advisory thresholds.

Tuesday...Moderate to high confidence.
Expecting a period of southwest wind gusts of 25 knots and 3 to
6 foot seas developing across our southern and eastern waters
during the afternoon. Small Craft Advisories have been issued.

Wednesday: Gusty winds up to 30 kt. Areas of seas approaching 5
ft. Slight chance of rain showers.

Outlook /Wednesday through Saturday/...

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of seas approaching 5 ft. Slight
chance of rain showers.

Wednesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas.

Thursday: Moderate risk for Small Craft Advisory winds with
areas of gusts up to 30 kt. Local rough seas.

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Local rough seas.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

Friday Night: Winds less than 25 kt. Slight chance of rain.

Saturday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Chance of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 5 PM Tuesday to 5 AM EDT Wednesday
     for ANZ232-235-237.
     Small Craft Advisory from 11 PM Tuesday to 2 AM EDT Wednesday
     for ANZ233.
     Small Craft Advisory from 2 AM to 8 AM EDT Wednesday for
     ANZ250.
     Small Craft Advisory from 2 PM Tuesday to 8 AM EDT Wednesday
     for ANZ254>256.

&&

$$
SYNOPSIS...EVT/BW
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...EVT
AVIATION...EVT/BW
MARINE...EVT/BW