Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 181726

Area Forecast Discussion
National Weather Service Taunton MA
126 PM EDT Sun Mar 18 2018

Dry but unseasonably cold weather will continue through Monday.
High pressure brings dry weather Tuesday. A coastal storm moves
up from the Mid Atlantic coast Wednesday and then moves off to
the east Thursday. High pressure brings drier weather Friday and
early Saturday.



130 PM Update...

Trends in the forecast remain on track for this afternoon.
Persistent northwest flow will continue across the region
resulting in some weak CAA. Soundings continue to show mixing up
to 925-850 mb which will result in winds gusts to near 20-25
kts through the afternoon. Otherwise, forecast temps appear to
be on track with highs in the low to mid 30s.


Yet another H5 shortwave rotates out of Quebec during the
evening hours, however bufkit shows the column remains dry. This
suggests mainly SKC conditions continuing. However, the close
passage of this wave, combined with a ridging nose from the NW
will keep winds elevated a bit again overnight, limiting the
radiational cooling. Min temps similar to this morning, mainly
the upper single digits and low teens for the NW. Upper mid
teens to low 20s closer to the coastlines.

Although the longwave trof settled near Newfoundland and
Labrador remains in place, sfc inverted ridging, tide to a 1020+
high pres in Quebec and Ontario will keep conditions quiet
through Mon. Given the draw is from CP regions, mainly dry,
mostly sunny conditions are expected through the day on Mon,
with only a low risk for late increasing CI ahead of coastal low
development well to the S late.

Modest warm advection in the low-mid lvls. H85 temps average
around -8C by late Mon. This should allow highs to be a bit
warmer than Sun, ranging from the low 30s in the coldest spots,
to the low 40s close to the E/SE coastlines.


Big Picture...

Southern stream dominates the larger scale flow with several
shortwaves embedded in the flow. One shortwave passes south of New
England Tuesday. Earlier model packages indicated this as turning up
the coast toward us, but now it remains weak and moves out to sea. A
second shortwave moves to the East Coast Wednesday.

Model solutions have converged on the Tuesday shortwave, but
continue to have problems with the Wednesday-Thursday system. The
ECMWF and GFS show similar surface patterns, with a center track 120
miles outside the benchmark, while the GGEM is much closer to shore.
Ensemble solutions continue to offer varying solutions close and far
off. We opted for a blend of the GFS ensemble and the ECMWF.
Confidence is low-moderate.


Monday night-Tuesday...

High pressure over Eastern Canada remains in control this period,
with mainly clear skies and light winds Monday night, then
increasing clouds Tuesday. It is possible that the Islands will see
some light snow Tuesday, but most precipitation should remain
offshore. Radiational cooling is favored Monday night, so we went a
couple of degrees under guidance. Temps in the mixed layer Tuesday
support max sfc temps in the 30s.

Tuesday night through Thursday...

As noted, models have given up on developing a coastal storm from
the first shortwave, but agree on generating a coastal off North
Carolina from a second shortwave Tuesday night/Wednesday. All models
send this northeast, with the GFS and ECMWF tracking it outside the
benchmark while the GGEM comes just inside. Past model uncertainty
holds us back on increasing pops much, but we will indicate chance
pops across RI and much of Eastern MA. The areal coverage is based
on the 0.1 inch QPF on the GEFS ensembles. The storm passes the
benchmark and moves off to the east Thursday morning, with any
precipitation expected to diminish at that time.


Shortwave ridge builds over the region Friday, reflecting similar
building by the sfc ridge over Northern Ontario. This ridge remains
in place through Saturday morning.

An ill-defined shortwave races east across the country, approaching
New England on Saturday. Models show different timing, with the GFS
fastest, GGEM slowest. They suggest timing for either late Saturday
or Saturday night, with temperature profiles supporting snow. We
will show a chance of snow Saturday night but with low confidence.


Forecaster Confidence Levels...

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

Short Term /through Monday/...High confidence.

Before 00z...VFR with gusts between 20-25 kts this afternoon.

After 00z...VFR. NW winds will continue with 4-6kft deck moving
through the region.

Monday into Monday night...VFR. NW winds generally lighter, but
could still see gusts near 20 kts.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Thursday/...

Tuesday: VFR. Breezy.

Tuesday Night: VFR, with MVFR developing after midnight. Windy with
gusts to 35 kt.

Wednesday: MVFR. Windy with gusts to 35 kt. Chance RA/SN.

Wednesday Night: MVFR. Windy with gusts to 35 kt. Chance SN.

Thursday: MVFR. Windy with gusts to 35 kt. Chance of SN eastern MA


Short Term /through Monday/...High confidence.

1PM Update...Went ahead an added Boston Harbor and Narragansett
Bay into the SCA. Winds are mixing just a bit stronger than prev
forecasted with NW gusts at or around 25kts. Winds will slacken
by this evening thus will let the SCA expire then.

Today and tonight...
Early day conditions are quiet across the waters. However, by
late afternoon and into the overnight winds will once again
increase out of the NW reaching around 25 kt and allowing wind
waves to reach 5 ft on the ocean waters. A new round of Small
Craft Advisories will be issued.

Winds/seas should diminish early, allowing small craft
conditions to subside through the day.

Outlook /Monday Night through Thursday/...

Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Slight chance of snow. Areas of
visibility 1 to 3 nm.

Tuesday Night: Low risk for gale force winds with gusts up to 35 kt.
Local rough seas. Slight chance of rain, slight chance of snow.
Areas of visibility 1 to 3 nm.

Wednesday: Moderate risk for gale force winds with gusts up to 40
kt. Rough seas up to 13 ft. Chance of rain, slight chance of snow.
Areas of visibility 1 to 3 nm.

Wednesday Night: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 18 ft. Chance of snow, chance of rain.
Visibility 1 to 3 nm.

Thursday: Low risk for gale force winds with gusts up to 35 kt.
Rough seas up to 18 ft. Chance of snow, slight chance of rain.
Local visibility 1 to 3 nm.


MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ232>235-237-
     Small Craft Advisory until 7 PM EDT this evening for ANZ230-
     Small Craft Advisory until 8 AM EDT Monday for ANZ231-251.
     Small Craft Advisory until 11 AM EDT Monday for ANZ250-254.


NEAR TERM...Dunten
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