Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 190039 

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
739 PM EST Mon Nov 18 2019

the coastal storm will continue to bring spotty light rain and
strong winds along the coast early tonight. The rain may become
a wintry mix across the interior high terrain late tonight into
Tuesday morning. Mainly dry and seasonably chilly weather
follows Tuesday afternoon into early Wednesday. Low pressure
passing south of the region may push some rain and snow showers
across central and eastern areas from midday Wednesday into
Wednesday night. Dry conditions and seasonable temperatures for
Thursday. An approaching front will bring a chance for showers
on Friday, then dry but colder conditions Friday night into
Saturday. Another system may approach Saturday night into
Sunday, but the details remain uncertain.


Near term /until 6 am Tuesday morning/...

7 PM update...

Temperatures topped off in the upper 30s and 40s across the
region today, with a few spots touching 50 across the Outer Cape
and islands. Readings remain above freezing across the region,
though have slowly fallen over the last few hours. Noting temps
in the mid 30s across the east slopes of the Berkshires and
Worcester Hills, so will start to see the rain start to mix with
sleet and/or freezing rain this evening as temperatures continue
to slowly fall.

Have continued to mention precip across the region, though early
tonight will see dry conditions mainly west of the Worcester Hills.
However, will probably see more moisture wrap S across the CT
valley and east slopes of the Berkshires. Latest NE regional 88d
radar loop showing a band of precip working swrd out of central
and NE mass, as well as another band of precip working eastward
out of the Hudson Valley. Also, another short wave works up the
coast overnight, which will bring another round of moisture

Have continue to mention mixed precip after midnight as the
colder air drains in on the northerly winds that will become
light overnight. With the better shot for mixed precip,
especially the threat of freezing rain or drizzle across northwest
mass overnight, have held on to the Winter Weather Advisory for
western Franklin and Hampshire counties.

Previous discussion...

Through the overnight hours, the next round of precipitation
approaches. This is associated with a potent mid level trough
lifting north out of the Delmarva, ushering out today's coastal
low, while bringing another slug of moisture with it. Pwats
>0.75" together with potent mid-level energy and favorable jet
dynamics aloft will bring fairly widespread rain showers to all
of southern New England generally after midnight into Tuesday
morning, with the greatest quantitative precipitation forecast amounts in western MA/CT.

Surface temperatures have been adjusted slightly warmer in line
with the latest hi-resolution guidance which has lessened the
magnitude of caa, decreasing the risk of appreciable snow/icing
overnight. However, in the highest elevations of the Berkshire
slopes, temperatures will hover at or near freezing, so can't
rule out a coating of snow or light glaze of ice early Tuesday
morning. For the possibility of some light freezing rain, a
Winter Weather Advisory continues through Tuesday morning for
western Hampshire and Franklin counties.


Short term /6 am Tuesday morning through Tuesday night/...

Tuesday starts wet before drying out by late morning/afternoon.
By 15z (10am) the core of the upper low is over Maine, along
with the bulk of the moisture. Looking through the column we see
some drier air working in in the mid and upper levels which
should allow for peeks of sun Tuesday afternoon. This will help
warm temperatures a bit too, even in the cold air advection pattern. High temps
should reach into the 40s for most, which, with light winds and
the emerging sun will be a nice change from today's wet, raw
weather. Tuesday night into Wednesday morning things stay dry
but we'll see increasing clouds. This as a deep mid level trough
digs to our south, eventually wrapping around enough moisture
to bring some rain and snow showers on Wednesday. Cold air advection pattern
will be evident overnight (850mb temps down to -2 to -3c), with
surface lows about 5 degrees colder than the night previous, in
the upper 20s and low 30s.


Long term /Wednesday through Monday/...


* light rain and/or snow showers push across central and
eastern areas Wed into Wed night as an offshore low passes.
Gusty northerly winds develop across the coastal waters.

* High pressure brings dry, seasonable weather on Thursday

* mild temperatures make a brief return ahead of an approaching
front, bringing showers Thu night and Fri, then dry but
colder weather late Fri night into Sat

* model solution spread lending to low confidence forecast for
potential approaching system sometime next weekend


An amplified but progressive mid level steering pattern
continues across the lower 48. 500 mb trough may bring some
unsettled conditions around mid week, but should push steadily
offshore. Will see a brief dry and seasonal day as progressive
500 mb ridge pushes across the eastern Seaboard. Cutoff 500 mb low
crosses eastern Ontario/Quebec, with a trailing surface front
swinging across Fri night into Sat.

Solutions amongst the 12z model suite signaling increasing
spread next weekend. This lends to rather low confidence as
another system may approach during this timeframe.


Wednesday and Wednesday night...

An amplified long wave trough, with a cutoff 500 mb low passing
close to or S of the region, will lift east-NE Wed afternoon into
Wed night. Looks like moisture will shift back across central
and eastern areas during the midday and afternoon hours before
moving offshore. May see some light snow showers across north
central areas, with mainly rain showers across eastern mass.
Mainly northerly winds in place, but temps will top off in the
upper 30s to lower 40s as most of the colder air holds back
until the trough shifts east.

Leftover showers linger across the mid and Outer Cape Wed
evening, then will exit rather quickly as drier air moves in on
northwest winds. Temps will bottom out in the mid-upper 20s well inland
to the mid- upper 30s along the immediate coast, which are
close to seasonal normals. Will see winds gusts up to 20-25 kt
across the Outer Cape and Nantucket, as well as across the
coastal waters.

Thursday and Thursday night...

500 mb ridge will steadily shift E, along with large surface high
pressure that will cross the eastern Seaboard. Northwest winds will
start off gusty especially along the coast, but will diminish as
the ridge builds east. Highs will range through the 40s.

As the ridge shifts offshore Thu night, will see light/variable
winds to start then becoming S-SW. This will allow temps to
bottom out Thu evening, then will slowly rise through the
remainder of the night. Clouds will also increase during the
night as the next system approaches. May see scattered showers
develop and move across mainly around or after midnight, with
the best chances across central and western mass, possibly into
north central CT.

Friday through Sunday...

Looks like showers will be scattered across the region through
Friday as the front pushes across, though there is some question
on the timing of this feature with increasing model solution
spread. Ahead of the front, temps will be mild. Expect readings
topping off from the mid-upper 40s across the higher inland
terrain to the lower- mid 50s across the coastal plain.

A lot of question remain in place for the upcoming weekend
weatherwise. Model solutions are spread out, mainly with how
each member is handling a potential southern stream system that
may try to lift NE. This is likely due to wide spread in the
handling of the mid level features, namely how fast the next
northern stream system moves along as well as a possible
southern stream short wave that may merge with the northern
stream system. For now, have started off dry, then could see
unsettled conditions. However, quite a bit of uncertainty so low
confidence forecast.


Aviation /00z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through Tuesday night/...moderate confidence.

23z taf update...

expect MVFR-IFR conditions. Another round of precip will move
in after midnight. Ptype mostly rain but changing to a wintry
mix with some freezing rain/snow possible over the higher elevations.
Lowest visibilities likely north and west of orh. Diminishing

MVFR-IFR conditions with patchy -ra across central/east terminals
and mixed precip mainly across the higher inland terrain early.
Conditions should improve to VFR from S-north from mid morning
through the afternoon as the precip lifts into northern New
England. Light west-northwest winds, up to 10 kt along east coastal

Tuesday night...
VFR conditions. Low chance of developing -ra across east coastal
terminals after 06z with local MVFR visibilities. Light west-northwest winds.

Kbos taf...high confidence in taf.

Kbdl taf...high confidence in taf.

Outlook /Wednesday through Saturday/...

Wednesday: MVFR/IFR conditions possible. Breezy. Slight chance
rain showers.

Wednesday night: mainly VFR, with local MVFR possible. Breezy.

Thursday: VFR. Breezy.

Thursday night: mainly VFR, with areas MVFR possible. Breezy.
Slight chance rain showers.

Friday: mainly MVFR, with areas VFR possible. Breezy. Slight
chance rain showers.

Friday night through saturday: mainly VFR, with local MVFR
possible. Windy with local gusts up to 30 kt. Slight chance
rain showers.


short term /through Tuesday night/...moderate confidence.

Gale warnings remain in effect for all waters except for small
craft advisories on Boston Harbor and Narragansett Bay. NE
gusts up to around 35 kt this evening, with strongest gusts
continuing across the waters south and east of Cape Cod. Seas
up to around 15 ft on the eastern outer waters.

The winds and seas will diminish tonight, with winds lowering
below small craft levels by late tonight. Vsbys reduced in rain
and fog, especially over eastern waters. Seas subside to 6-10
ft by Tuesday morning.

Expect west winds at 5-10 kts on Tuesday. Seas up to 5 to 9 ft,
highest on the eastern outer waters early, then slowly
subsiding but remaining at or above 5 ft through the day.

West-northwest winds at around 10 kt early Tuesday night will shift to north
after midnight, with gusts up to around 15 kt. Seas will linger
at 5 to 6 ft across the outer waters through most if not the
entire night.

Outlook /Wednesday through Saturday/...

Wednesday: low risk for Small Craft Advisory winds with gusts
up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Wednesday night: moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain

Thursday: low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft.

Thursday night: winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers.

Friday: low risk for Small Craft Advisory winds with gusts up
to 30 kt. Local rough seas. Chance of rain showers.

Friday night: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of
rain showers.

Saturday: low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of rough seas. Slight chance of rain showers.


Tides/coastal flooding...
astronomical high tide at Boston is 10.3 ft MLLW, and 3.7 ft
MLLW at Nantucket Harbor. A storm surge of 1.5 to 2 ft is
expected during the high tide this afternoon, and current
observations show that that is right on track. The combination
of the surge and seas up to 15 ft offshore are resulting in
pockets of splashover or minor coastal flooding for much of the
eastern Massachusetts coast during the high tide with the greatest risk at
Nantucket. Somewhat lesser risk along the North Shore which will
be furthest removed from the low level jet.

A coastal flood advisory remains in effect for the eastern mass
coast including Nantucket. However, the winds and storm surge
will not be high enough to cause a significant coastal flood


Box watches/warnings/advisories...
Massachusetts...Winter Weather Advisory until 6 am EST Tuesday for maz002-008.
Rhode Island...none.
Marine...Gale Warning until 9 PM EST this evening for anz231-232-251-
Gale Warning until 7 PM EST this evening for anz233>235-237.
Small Craft Advisory until 9 PM EST this evening for anz230-
Gale Warning until 10 PM EST this evening for anz250-254.


near term...evt/bw

National Weather Service Glossary of Abbreviations