Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 242239
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
639 PM EDT Sat Sep 24 2016

.SYNOPSIS...
Cool and dry weather this weekend will continue into early next
week. Low pressure may bring showers to southern New England some time
late Monday night into Wednesday morning.  Otherwise, seasonable and
mostly dry weather is expected much of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
640 PM Update...Not much to update this evening with the forecast
generally on track.

Tonight...High pressure building into the region from the north
and west. Radiational cooling setup as the boundary layer
decouples allowing for winds to become light beneath clear
conditions. Though still a decent pressure gradient along the E/SE
coast yielding some coastal and offshore NW winds thereby making
it milder. Forecasting lows around the upper 30s with coldest
conditions over N/W MA with the likelihood of some frost, warmest
over the E/SE shore. Focus upon areas which are prone to radiate.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Sunday...Unseasonably cool and mostly sunny. Highs topping out
around the mid to upper 60s as the coldest of airmass at H85
sweeps through the region, but still stepped up a degree or two
given the sun angle and dry conditions across the region. Quite
the autumn feel. Worth nothing, such an H85 airmass, around +2C,
close to the record lowest observed of just slightly below
freezing per Chatham MA sounding climatology. Overall light winds
but still a bit breezy along the E/SE coast. Went with deep-layer
mixing of the boundary layer, so expect a mix down of drier air
with dewpoints possibly into the 20s and breezy N winds along the
E/SE coast with gusts up to 20 mph possible.

Sunday Night...Given a chilly day and high pressure settling in
over central New England overnight, am going to lean very low and
close to record low temperatures given the synoptic setup. This
gives a forecast low temperature range around the low to mid 30s
for much of Southern New England. See the climate section below
for September 25th and 26th record low temperatures. Clear
conditions, light winds overall.

Am concerned. Thinking an anomalous situation given dry conditions
across the region coupled with the radiational cooling setup. Wonder
whether guidance is capturing this rather well. A hunch that perhaps
there`s an opportunity here to undercut guidance by a couple of
degrees. Feel Sunday morning lows, if lower than initially thought,
will weigh on confidence and forecast thinking going into Monday
morning.

Rather than going with double-headlines, have kept with the frost
advisories for tonight going into Sunday morning, while highlighting
the Monday morning impacts in the hazardous weather outlook. Could
be looking at headlines over much of southern New England as
frost conditions are possible in the E/SE interior of
Massachusetts.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
HIGHLIGHTS...
* Seasonable temperatures expected much of the long term
* Low pressure may bring a chance of showers Mon. night to Wed.
* Quite a bit of uncertainty in the pattern for late next week

Operational models show quite a degree of spread in the synoptic
pattern for next week.  In addition, both the GEFS and the EPS
members are spread over a couple of solutions.  Much of this lays in
how progressive the pattern will be, particularly across the NE. The
slower solutions, including the ECMWF, keep the NE out of the
westerly flow, allowing for the upper trough in the Great Lakes
Monday morning to stall over the eastern US for much of the week.
The more progressive models, including the Canadian, keep things
moving, allowing the trough to move through southern New England and
offshore.  The GFS finds itself in the middle of the ensemble means,
being a fairly good compromise on the speed.  However, all of this
spread leads to quite a bit of uncertainty especially Wednesday and
beyond.

Monday...High confidence.  High pressure over southern New England
will be the main influence for the weather.  After a chilly morning,
temperatures will rebound to near normal for late September.  Still
a shock after all the warm weather we`ve been having.  Pleasant,
dry, with full sun, it should be a nice day as the high slowly moves
off to the south and east.

Monday night through Wednesday morning...Moderate confidence.  As
the high moves offshore Monday night and a broad upper level trough
moves into the Great Lakes, low pressure and a cold front will have
some effect on southern New England.  There is already some spread
in the models for this time frame with the GFS again a bit more
progressive than the ECMWF.  The primary low pressure will be over
the Great Lakes but both models indicate a secondary low developing
somewhere around southern New England.  The exact timing and
placement of this development will have some effect on the timing
and location of showers.  However, there is expected to be some
showery weather sometime during this time frame.  The GFS is a
little speedier, moving it out Tuesday night, while the ECMWF keeps
a chance of showers continuing into Wednesday, particularly on the
south coast.  Will stick with high end chance to low end likely PoPs
for much of this time frame.  Otherwise, temperatures will continue
to be seasonable with highs in the upper 60s to around 70 and lows
in the upper 40s to mid 50s for most.

Wednesday afternoon through Saturday...Low confidence.  As mentioned
above, much of this time frame will depend on how quickly the upper
level trough is allowed to exit the east coast.  The ECMWF is one of
the slowest solutions, keeping the upper trough over the eastern
half of the CONUS through Saturday.  The GFS is one of the faster
operational solutions, but in the midst of the ensemble members, and
moves the upper trough out by Friday morning, allowing for some
upper level ridging to begin.  The main difference in sensible
weather will be either a prolonged period of northeasterly winds and
clouds and periods of showers, per the ECMWF.  Or it will be drier
with high pressure building into the region.  Temperatures will
remain seasonable either way.  Will stick with a model blend for
this time period, with a bit more weight given to the GFS given its
place in the midst of the ensemble members.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels.

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

Short Term /through Sunday Night/...High confidence.

VFR. N/NW winds 20 to 25 kts especially during the daytime
periods lingering into evening. Still breezy along the E/SE coasts
overnight around 10 kts while light winds elsewhere. SKC.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday night through Wednesday morning...Moderate confidence. Mainly
VFR with periods of MVFR in scattered showers.

Wednesday afternoon through Thursday...Low confidence.  Most likely
VFR for much of this time, but model uncertainty could mean periods
of MVFR in lower clouds and scattered showers.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Sunday Night/...High confidence.

This afternoon...

Small craft boaters should be aware of the persistence of N winds
upwards of 20 kts through much of the afternoon, settling towards
evening under the influence of high pressure. Seas holding around
5 feet thus will continue the small craft advisories where the
threat of 5 foot seas and gusts up to 25 kts is more likely.

Tonight into Sunday...

Resurgence of NW winds to near 25 kt will likely require near
shore waters to once again have a small craft advisory, and
continue the ocean waters. Seas will be the issue tomorrow,
dropping from about 6-7 ft through the day.

Outlook /Monday through Thursday/...

Monday...High confidence.  Quiet boating weather expected with winds
and seas remaining below small craft criteria.

Monday night and Tuesday...Moderate confidence.  Winds and seas
increase as low pressure approaches southern New England from the
west.  Small craft conditions likely.  There is a low probability of
southerly gale force gusts being reached on Tuesday.  In addition,
visibilities may be reduced at times in showers and fog.

Wednesday and Thursday...Low confidence.  Small craft conditions may
continue, particularly on the outer waters for a time.  It will
depend on which model solution verifies.  See long term section for
more meteorological explanation.

&&

.CLIMATE...
Record low temperatures...

September 25th / 26th (last set in...)

Boston ....... 38 (1950) / 34 (1879)
Hartford ..... 30 (1963) / 33 (1978)
Providence ... 36 (1963) / 37 (1967)
Worcester .... 31 (1944) / 28 (1925)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Frost Advisory from 2 AM to 8 AM EDT Sunday for MAZ002>004-008.
RI...None.
MARINE...Small Craft Advisory from 4 AM to 11 AM EDT Sunday for
     ANZ231>235-237-251.
     Small Craft Advisory until 3 AM EDT Monday for ANZ250-254-255.
     Small Craft Advisory until 4 PM EDT Sunday for ANZ256.

&&

$$
SYNOPSIS...RLG/Sipprell
NEAR TERM...RLG/Sipprell
SHORT TERM...Sipprell
LONG TERM...RLG
AVIATION...RLG/Sipprell
MARINE...RLG/Sipprell
CLIMATE...Sipprell



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