Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 250531
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1231 AM EST Sat Nov 25 2017

.SYNOPSIS...
After a cold night, milder air returns Saturday ahead of a cold
front. The cold front moves through southern New England
Saturday night accompanied by scattered showers. Blustery and
colder weather follows Sunday. Milder temperatures may return
Tuesday and Wednesday before cooler weather returns later in the
week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1230 AM Update...

Clear skies at the moment, but high-res models still insistent
that low clouds will develop before daybreak across southern RI
and southeast MA, especially on Cape Cod and Islands as moisture
becomes trapped beneath inversion. Temperatures have bottomed
out in 30s, with some upper 20s as of midnight, but readings
should begin to recover overnight as light SW winds develop.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
Saturday...

Low clouds in southeastern MA and southern RI should
break apart by mid morning. Otherwise, sunshine will give way
to increasing cloudiness as a cold front advances toward
southern New England. High temperatures will be well above
normal as southwest winds continue ahead of a cold front. Winds
could gust to 20+ mph along the immediate coast and in the
Worcester hills. The day should be dry, except there is a slight
chance that showers could reach northwestern MA toward sundown.

Saturday night...

Cold front moves across the region from west to east, bringing
scattered showers with it. The best chances...40 to 45
percent...will be in eastern MA, where the moisture content of
the air is higher. Only a few hundredths of an inch of rainfall
is expected at any given location. South to southwest winds will
shift to the west-northwest late. Lows will drop to the 30s
again behind the front, except 40 to 45 Cape Cod and the
islands.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Big Picture...

Longwave trough lingers over the Eastern USA much of the period, but
with a flattening trend. Shortwave pattern shows a shortwave moving
through a zonal flow. One shortwave moves through New England
Sunday, with lingering troffiness over the area on Monday. A ridge
builds for Tuesday, then a more shallow shortwave races across on
Wednesday. Another shortwave, this one a little deeper, reaches New
England toward the end of next week.

Model mass fields are in general agreement east of the Rockies
through Wednesday. Mass and thermal fields with a shortwave moving
in off the Pacific Ocean show less agreement with that feature
during most of the forecast period up through the time it reaches us
the end of next week. Confidence in the forecast is strong through
midweek, but low-moderate on next Friday.

Contour heights are lower/colder than normal Sunday and Monday, then
trend above normal midweek, then trend lower/colder again by Friday.

Details...

Sunday-Monday...

Upper trough digs over New England Sunday. Cold pool will be in
place with 500-mb temps at -30C, which will destabilize the airmass.
Moisture lingers below 800 mb during this time. Expect quite a few
clouds to pop during the day, possibly a few flurries in the north.
Mixed layer temps will support max sfc temps in the upper 30s and
40s. Winds in the mixed layer reach 20-25 knots in the ECMWF and 30-
35 knots in the GFS. Either way, expect gusty northwest winds.
We took a blend of the two.

The trough and cold pool move off on Monday and high pressure builds
surface and aloft. Could be some lingering clouds Monday but should
trend to less sky cover during the day. Expect a fair day with max
sfc temps in the 40s.

Tuesday through Thursday...

Developing southwest flow brings milder air to the region Tuesday.
Another cold front crosses New England Wednesday, but with most of
the curvature and the core of the upper jet over VT/NH/ME. Expect a
cold frontal passage during the day, with a few clouds and a wind
shift, but otherwise dry.  High pressure builds with dry weather
Thursday. Temperatures cool a little from Wednesday.

Friday...

Cold front moves through during the day, but differences among the
models upstream lead to uncertainty in the timing as well as the
stability of this solution. GFS and ECMWF currently show the
showers starting early Friday morning and end them toward
evening.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

High confidence through Sunday.

MVFR ceilings around 015 may develop across southern RI and
southeast MA 09Z-15Z, especially on Cape Cod and Islands. Otherwise
VFR today with S-SW winds gusting to 20-25kt this afternoon,
especially near coast. VFR ceilings 040-060 develop from W to E
this evening with isolated -SHRA, which end overnight as winds
shift to W. VFR with increasing W/NW winds Sunday. Could see
brief period of snow flurries during morning.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

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

Sunday Night through Wednesday: VFR. Breezy Monday.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...

Tonight and Saturday...Moderate confidence.

Small Craft Advisories are in effect for the waters off of the
east coast of MA for southwest winds gusting to 25 kt late
tonight into Saturday. This is based on some downward mixing of
a low-level jet of 35-40 kt late tonight into Saturday. Winds
are expected to remain below 25 kt over the southern waters Sat.
Seas will mainly be in the 3-4 ft range across all outer
waters.

Saturday night...Moderate confidence.

A cold front exits the coastal waters late at night. The
Advisory situation is a little tricky. We have allowed the SCA
for the eastern waters to expire at 00Z Sunday as previously
forecast because winds are expected to diminish for much of
Saturday night (but will pick up to SCA levels again on Sunday).
A Small Craft Advisory has been issued for the southern outer
waters after 06Z Sunday because northwest winds behind the
front will mix to 25 kt and seas may increase to 5 ft after
about 1 AM Sunday. We continued the SCA for those areas through
Sunday afternoon. For the bays and sounds close to the south
coast, seas should remain below 5 ft and winds are not expected
to increase to SCA thresholds until Sunday, so future shifts
will likely need to hoist the SCA for these waters and for
eastern waters, as time gets closer to the event.

Outlook /Sunday Night through Wednesday/...

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

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas.

Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Areas of seas approaching 5 ft.

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

Tuesday: Winds less than 25 kt.

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of seas approaching 5 ft.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ250-
     254.
     Small Craft Advisory until 2 PM EST this afternoon for ANZ251.
     Small Craft Advisory from 1 AM to 6 PM EST Sunday for ANZ255-
     256.

&&

$$
SYNOPSIS...WTB/GAF
NEAR TERM...JWD
SHORT TERM...GAF
LONG TERM...WTB/GAF
AVIATION...JWD
MARINE...WTB/GAF


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