Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 191056

Area Forecast Discussion
National Weather Service Taunton MA
656 AM EDT Mon Mar 19 2018

Dry but unseasonably cold weather will continue through
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.



7 AM Update...

Patch of clouds is shifting offshore to the southeast. This is
likely associated with the shortwave moving across Southern New
England. With all of this moving offshore, expect mainly clear
skies through the day. Temperatures at 7 AM were 15-25, which is
a little less cold than the hourly temperature forecast for that
hour. But temperatures aloft still support the expected max sfc

So no changes planned to the forecast.

Previous Discussion...

WV imagery shows the kicker shortwave currently moving across
Maine this morning. While this is mostly without fanfare, there
is a layer of moisture, narrow in perspective which is yielding
a band of BKN-OVC SC shifting ESE through the S tier of the
region this morning. Given very weak echos within this band,
cannot rule out a few flurries. However, these are unlikely to
measure, as even in these areas dwpt depressions are on the
order of 5-10F with ceiling heights in the 5-8kft range. The
band of SC will continue to shift offshore, such that most of
the region currently under BKN/OVC conditions will be trending
toward SKC shortly after sunrise.

Otherwise, behind this wave, and ahead of converging N and S
stream waves, H2 to H5 flow becomes confluent allowing the sfc
high pres to ridge into New England from the NW. Sounding
response yields dry/subsidence. Mostly sunny conditions are
expected through the day. If anything H85 temps may increase
slightly through the day, along with H92 temps which may be what
mixing is limited too thanks to the strong subsidence
inversion. Temps at this lvl avg around -6C. This will lead to
highs in the low-mid 30s across NW MA, while coastal areas in
the mid 30s to around 40 are expected.


Inverted ridging remains in control overnight. Increasing clouds
expected, mainly in the form of advancing CI shield ahead of the
first coastal storm development S of the Delmarva. Although
winds should be weak, the increasing moisture aloft may limit
the ability for radiational cooling a bit. Will allow mins to
fall into the teens, but less so into the single digits as they
had under clear skies previous nights.

Although the first, dominant S stream wave continues to feature
gradually deepening low pres well to the S, confluence aloft is
dominant across New England and the bufkit continues to show
strong subsidence as a result. Therefore, with all deterministic
and ensemble guidance supporting the QPF shield remaining
offshore, will follow suit, keeping Tue dry.

Filtered sunshine (through increasing CI) should still allow BL
to mix well especially as the subsidence inversion diminishes
somewhat. Low lvl temps near the top of the mixed layer becomes
nearly isothermal, about -4C to -6C. So a few more spots should
reach the low 40s, while the remainder of the region holds in
the 30s.


Big Picture...

Southern stream crosses the southern USA. One shortwave digs in over
the southeast USA Tuesday night, turning the upper flow up the coast
over New England. Closed low within this trough moves up the coast,
crossing New England Wednesday night and the Maritimes Thursday.
Northern stream trough drops down from Canada over the weekend.

Model solutions are similar through Saturday morning with
differences in detail after that. However, run-to-run differences
continue and so forecast confidence is low-moderate.


Tuesday night through Thursday...

Upper flow turns from the south Tuesday night, supporting a scenario
for increasing moisture flow toward Southern New England.
Precipitable water values climb to between 0.5 and 0.75 inches,
which is above average for the equinox but not excessively so.

All models develop coastal low off North Carolina Tuesday afternoon
and then move it northeast, passing near the benchmark either
Wednesday or Wednesday night. The GFS and GGEM are similar in timing
this passage late afternoon/evening, while the ECMWF is slower with
passage Wednesday night. This track is about 70 miles farther north
than previous model runs, which would push precip farther north with
a better chance to affect Southern New England Wednesday.
Temperatures Wednesday will be borderline for accumulation, even
after accounting for wet bulb processes. Even so, the scenario as
presented shows potential for some snow accumulation, with a 4-5
inch bullseye in Southeast Mass with amounts diminishing toward the

Strong low level jet on the north side of this storm, with winds 50-
60 knots aloft. This should support northeast wind gusts 35-40 knots
at the surface. A wind advisory may be needed for parts of Eastern
Mass, especially the Cape and Islands.

The forecast brings likely pops into Southern RI and Southeast Mass
Wednesday with chance pops southeast of Fitchburg to Springfield MA.

The low moves off to the northeast Thursday, and northwest winds
bring drier air into our area that should aid in partial clearing.


Upper cyclonic flow lingers over New England Friday. Otherwise dry
weather with seasonably cool temperatures.


Northern stream trough dives south from Canada Saturday night and
sweeps over New England Sunday. This by itself may be enough for
some flurries or light snow showers. Another shortwave moving
through the southern stream passes south of us Sunday. Either source
would be good for chance pops for rain or snow. Forecast confidence
is low.


Forecaster Confidence Levels...

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

Short Term /through Tuesday/...High confidence.

Today... VFR. NW winds with a few gusts 15-20 kt.

Tonight... VFR. Weaker NW winds.

VFR through the day with increasing high and mid clouds. Winds

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

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

Tuesday Night: Mainly VFR, with local IFR possible. Windy with gusts
to 35 kt. Slight chance SN.

Wednesday: MVFR/IFR conditions possible. Strong winds with gusts to
45 kt, mostly in Eastern Mass. Chance SN.

Wednesday Night: MVFR/IFR conditions possible. Strong winds with
gusts to 50 kt, mostly in Eastern Mass. Chance SN.

Thursday: Mainly VFR, with local MVFR possible. Strong winds with
local gusts to 40 kt

Thursday Night: VFR. Breezy.


Short Term /through Tuesday/...High confidence.

Today into Tuesday...
NW winds diminish today below the 25 kt threshold by about mid
day. This will also allow the 5-6 ft wind driven waves to
diminish. The small craft advisory on the E waters should be
allowed to dissipate, along with the risk for further freezing
spray. After these conditions subside, quiet boating weather
continues into Monday.

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

Tuesday Night: Low risk for gale force winds with gusts up to 40 kt.
Local rough seas. Chance of rain, slight chance of snow.
Areas of visibility 1 to 3 nm.

Wednesday: Moderate risk for gale force winds, and low risk for
storm force winds. Gusts up to 50 kt. Rough seas up to 16 ft. Snow
likely, rain likely. Visibility 1 to 3 nm.

Wednesday Night: Low risk for storm force winds with gusts up to 50
kt. Rough seas up to 17 ft. Chance of snow, rain likely.
Visibility 1 to 3 nm.

Thursday: Moderate risk for gale force winds early with gusts up to
40 kt. Winds diminishing by afternoon. Rough seas up to 16 ft. Local
visibility 1 to 3 nm.

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

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


MARINE...Gale Watch from late Tuesday night through Wednesday evening
     for ANZ231>235-237-250-251-254>256.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ231-
     Freezing Spray Advisory until 2 PM EDT this afternoon for
     Small Craft Advisory until 2 AM EDT Tuesday for ANZ250-254.


MARINE...WTB/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.