Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 201943

Area Forecast Discussion
National Weather Service Taunton MA
343 PM EDT Fri Oct 20 2017

High pressure will move from the Appalachians today to a
position east of New England on Sunday. The high will bring
warm dry weather for Sunday and Monday. A cold front brings
showers Tuesday and Wednesday. Cooler drier weather returns
late in the week.



4 PM update...

Dry and pleasant weather continues into tonight as deep layer
ridge and associated subsidence over the eastern Great Lakes
advects toward New England. Surface high over western PA moves
slowly eastward and relaxes the pressure gradient across our
area. This will result in wind diminishing with sunset along
with clear skies and a very dry atmosphere. Thus temps will fall
quickly with sunset given dew pts are in the 30s. Therefore
have sided with the coolest guidance for overnight lows with
mins in the 40s and even a few upper 30s in the CT river valley
of western MA. Nevertheless these temps are still a few degs
above normal for late Oct




Subtropical ridge currently over the southeast states builds
northward up the eastern seaboard Saturday. Surface high moves
from eastern PA early Sat to south of New England during the
afternoon, yielding light SW winds across the area. Surface
pressures higher tomorrow (1024 mb) than today (1017 mb) across
New England. This will result in less blyr mixing but entire
column continues to warm with 925 mb temps warming from +11C
today to +16C tomorrow. This will yield highs in the mid to
upper 70s, likely falling shy of the records but still very
pleasant with dew pts in the 40s, light winds and lots of

Record highs are 80 at Worcester, 81 at Providence, and 82 at
Hartford and Boston...all set back in 1920.

Saturday night...

High pressure lingers over the area so expect dry weather along
with temps falling quickly with sunset given light winds, dry
atmosphere and clear skies. Although not as cool as tonight as
southwest winds Sat bring dew pts up into the 40s.



Big Picture...

Ridge over the Eastern USA early in the week with above normal 500-
mb heights foretells a mild dry start to the week. High amplitude
trough digs over the Central USA during this time with a closed low
forming over the Great Lakes by Tuesday. The low then sweeps east
across New England Thursday-Friday. As the upper low approaches and
then moves overhead, 500-mb heights over us will lower
substantially, from the 580s to the 550s, which suggests much
cooler temperatures later in the week.

Mass fields begin to diverge Tuesday as the upper low formation
takes off to our west-southwest. Thermal fields are similar through
Wednesday then diverge. High confidence in forecast Sunday and
Monday...confidence then diminishes through moderate the rest of the



High pressure to our east with a light southerly flow across
Southern New England. The period will be subsident with warm
tempertures aloft. Main question will be the depth of the mixed
layer with shallow mixing promoting cooler temps. Mixing to 900 mb
would tap a 10C equivalent, while 925 mb would tap an 8-9C
equivalent. Expect max temps in the 70s, possibly 80 if the mixing
goes deeper. Dew points in the 50s suggests min temps mainly in the


The digging upper trough, associated surface cold front, increased
southerly flow ahead of the front, and increased moisture in that
flow all point to a chance of showers Tuesday and Tuesday night with
lingering showers Wednesday. Precipitable water values climb to 1.5
inches Tuesday and may reach 2.0 inches just ahead of the cold front
Tuesday night. Totals are forecast to reach upper 40s and LI values
marginally sub-zero, so thunder is not out of the question,
especially just ahead of the front.


Upper trough moves across on Thursday. High pressure builds on
Friday. Could be some leftover showers Thursday especially in
Eastern Mass. Dry weather Friday.


Forecaster Confidence Levels...

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

Short Term /through Saturday Night/...Generally high confidence.

2 PM update...

High pressure provides VFR, dry weather and light winds tonight,
Sat and Sat night.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday Night: VFR with local IFR in fog.
Monday: VFR.
Monday Night: VFR, with local IFR possible in fog. Chance SHRA
Tuesday: MVFR, with local IFR possible. Breezy. Likely SHRA.
Tuesday Night: MVFR, with local IFR possible. Breezy. Likely
Wednesday: Breezy. Chance SHRA.


Forecaster Confidence Levels...

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

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

4 PM update...

Very tranquil boating weather for late Oct with high pressure
building across the area through Sat night. Expecting light
winds, dry weather and good vsby thru this period.

Outlook /Sunday through Wednesday/...High confidence.

Sunday through Sunday Night:  Winds less than 25 kt.
Monday:  Winds less than 25 kt. Seas locally approaching 5 ft.
Monday Night:  Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.
Tuesday:  Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas. Chance of rain showers.
Tuesday Night:  Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 11 ft. rain showers
Wednesday:  Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Rough seas up to 12 ft. rain showers Likely.


Dry weather continues through at least Sunday with minimum RH
values Saturday down to 25 to 35 percent. However with high
pressure nearby winds will be very light. Thus fire weather
parameters remaining below headline criteria.


Record high temperatures for Saturday, October 21:
BOS 82 in 1920
BDL 82 in 1920
PVD 81 in 1920
ORH 80 in 1920




NEAR TERM...Nocera
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