Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 231427

Area Forecast Discussion
National Weather Service Boston/Norton MA
1027 AM EDT Fri Mar 23 2018

A series of upper level disturbances impact the region into
Sunday with occasional rain and snow showers, but these will be
hit and miss. Conditions improve with high pressure on Monday,
then a warming trend is expected through the middle of the week.


Upper trough continues to hang over NY and Ontario with a light
southwest upper flow over Southern New England. Mid and high
clouds remain over Southern New England but thin enough for some
sun in spots. Temperatures at 10 am were in the upper 30s and
low 40s.

This shortwave will move east into New England late this
afternoon and cross during the night. Model moisture fields show
increasing/thickening moist layer through the afternoon, so we
expect clouds will thicken/lower during this period.

The 12Z ALY sounding showed a low level inversion, but then
lapse rates near dry adiabatic from 900 mb to about 750 mb. This
may allow some spot rain/snow shower development this afternoon
especially in Western Mass.

Based on 10 AM temps, we nudged temps up a couple of degrees,
with a regional range of 39 to 49.


Typical diurnal ending for temps this evening will be assisted
by implied AVA with the passage of the shortwave/vort max. This
should also lead to some breaks in the lower-mid lvl cloud
cover. However, noting that upper lvl moisture increases, so
even as low-mid clouds disperse somewhat CI is likely to fill in
the gaps. This should limit cooling, especially given sfc pres
gradient remains strong enough to maintain a slight N-NW wind
overnight. Mins similar to this morning, mid 20s in coldest
spots to the low 30s elsewhere.

Given very little change in the downstream pattern (mean trof
to the E but with enough in place across New England to maintain
impact), expect another round similar to Fri as a second
shortwave shifts out of the Boreal regions of Quebec. This more
arctic influenced wave may in fact cutoff as it makes its
approach late Sat, yielding a sfc response even stronger
(better f-gen and convergence than Fri`s passage). It also
carries with it generally higher moisture through the column,
especially as winds shift toward and E component. Although
lower lvl lapse rates may not be as steep with a colder airmass
in place, the other dynamics look to make up the difference in
this case. Therefore, expecting more widespread snow/rain
showers than Fri, and have POPs at SCT category as a result.
Lower lvl temps/particularly wet-bulbs are near freezing, so
some of these could see light-mod snowfall. Sfc temps are mild,
so any accums should be limited even on grassy surfaces.

High temps a bit cooler thanks to reinforcing shot of cold air.
Mainly low to upper 30s rather than widespread 40s expected



00Z model suite continues to signal an overall amplified mid
level steering pattern across North America and beyond through
the majority of the long term period. H5 long wave troughing and
disturbances in the N-NE flow at the surface and aloft will
keep an unsettled pattern across the region through at least
this weekend.

As an H5 long wave trough slowly moves into the western states
early next week, the east coast trough will slowly shift
offshore, with ridging building from Hudson Bay to the lower
Mississippi valley. This will be slow to shift east through the
remainder of next week as cutoff mid level low pressure and
surface system lingers across the western Atlantic. Will likely
keep a cool onshore flow continue into early next week, then
should start to see temperatures slowly moderate as the ridge
builds to the west, bringing winds around to S-SW by around mid
to late next week.


Saturday night and Sunday...
H5 cutoff low pres moves across the region out of eastern
Quebec and the Maritimes, bringing scattered rain and/or snow
showers. Have carried CHC POPs across most areas, except only
slight CHC POPs across the mid and lower CT valley into W RI Sat
night into early Sun. As the low rotates S off the coast by
Sunday morning, will see the chance for precip dwindle from W-E,
with the best chance for precip across E coastal areas.

Will also see NE winds increase, with gusts up to 25-35 mph
along E coastal areas as well as on the islands. With the stiff
onshore wind, temps will run well below seasonal normals.
Expect highs on Sunday from the mid to upper 30s across most
areas, except around 40 across the CT valley.

Sunday night through Monday night...
As high pressure slowly shifts E during this timeframe, will
see dry conditions but continued cool temperatures as NE winds
will persist as the high center remains over Quebec. Highs
Monday will be a bit milder, but will still remain in the mid-
upper 30s along E coastal areas.

Tuesday through Thursday...
Some model solution spread noted during this timeframe. A
leading warm front pushes NE, which may bring a few rain and/or
snow showers reach as far E as central MA/NE CT. Expect to see
temps slowly moderate, reaching close to seasonal levels by
Thu, while the cold front hangs up around the eastern Great


Forecaster Confidence Levels...

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

Short Term /through Saturday/...

Through Tonight...High confidence.
Mainly VFR. SCT CIGS become BKN-OVC between 040-060
from mid to late afternoon into the evening, along with
isolated SHSN/SHRA with little to no accumulation. Showers
dissipate overnight with CIGS lifting closer to 10kft. W-NW
winds, mainly around or less than 10kt.

Saturday...High confidence.
Mainly VFR again, but occasional MVFR CIGS/VSBYS in more
widespread SHRA/SHSN than Fri. Winds shift from NNW to NE
through the day.

KBOS Terminal.  High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...Moderate Confidence.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHSN.

Sunday: Mainly VFR, with local MVFR possible. Windy with gusts
to 30 kt. Slight chance SHSN.

Sunday Night: VFR. Windy with areas gusts to 30 kt.

Monday: VFR. Windy with local gusts to 30 kt.

Monday Night through Tuesday: VFR. Breezy.


Short Term /through Saturday/...High confidence.

This afternoon... Winds continue to diminish, and should remain
below small craft thresholds out of the NW from now on.
However, a lingering swell tied to offshore low pres will keep
mainly E waters above 5 ft through the afternoon. Small Craft
Advisories will remain up until these diminish, about mid

Main change with this forecast is to extend Small Crafts for
Mass/Ipswich Bays and Cape Cod Bay through 18Z. Buoy 013 still
reports 5 feet as of 920 am.

Overnight into Sat...
Overall quiet boating weather is expected through this period.
Winds will gradually shift toward the N then NE by late Sat.
Gusts to 20 kt at peak, and while this may lead to a few wind
waves near 5 ft, these should be very limited. No headlines

Outlook /Saturday Night through Tuesday/...Moderate Confidence.

Saturday Night: Low risk for Small Craft Advisory winds with
local gusts up to 30 kt. Seas locally approaching 5 ft. Chance
of snow showers, chance of rain showers.

Sunday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Slight chance of snow showers.

Sunday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 12 ft.

Monday: Moderate risk for Small Craft Advisory winds with local
gusts up to 30 kt. Rough seas up to 11 ft.

Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft.

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 15 ft.


MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ231-
     Gale Watch from Sunday morning through Sunday evening for


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