Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 180822

Area Forecast Discussion
National Weather Service Taunton MA
422 AM 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.


With the mid-late afternoon frontal passage from yesterday,
drier air continues to filter in from the N-NW. Dewpoints early
this AM are in the single digits below 0F across much of the
region, and near 0F elsewhere. Even though SKC conditions have
persisted all night, decoupling has not been as widespread as
initially forecast thanks to slightly rising heights,
maintaining a slight N-NW breeze early this morning. Still
ambient temps are in the teens and low 20s, while wind chill
values are mostly in the single digits, certainly one of the
colder mornings we have had so far.

WV imagery shows two very small and progressive waves which
should pivot out of the N through the day today. However, the
column remains mostly dry, suggesting these waves pass with
little fanfare, in fact except for a few-sct clouds across the
SW portions of the forecast area, conditions should remain SKC
through the day.

Initially, the combination of a cold start and slight cold
advection leading to H85 temps dropping to near -15C by 18Z,
should limit highs today in the upper 20s to low 30s across NW
MA, and 30-40 across the E and CT valley where a slight
downsloping motion should be realized.


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.

Through this evening...
VFR. FEW-SCT CU mainly 040-060 across SW MA/CT this evening.
Winds mainly N-NW gusts to around 20 kt occasionally this

Tonight into Mon...
VFR. NW winds generally lighter than previous days, mainly
around 10 kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: VFR.

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.

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 from 5 PM this afternoon to 2 AM EDT
     Monday for ANZ232>235-237-255-256.
     Small Craft Advisory from 5 PM this afternoon to 8 AM EDT
     Monday for ANZ231-251.
     Small Craft Advisory from 5 PM this afternoon to 11 AM EDT
     Monday for ANZ250-254.


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