Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 151531 
afdbox

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
1031 am EST sun Dec 15 2019

Synopsis...
mainly dry but windy weather is on tap for the region today.
Low pressure moves out of the mid Mississippi and Ohio River
valleys Monday. This low will push south of the region Monday
night and Tuesday, bringing light snow, ice and rain. An Arctic
front moves across Wednesday with patchy light snow across
western areas as well as Cape Cod and the islands. Dry
conditions move in for late this week, with very cold
temperatures on Thursday, then readings may moderate a little
on Friday.

&&

Near term /until 6 PM this evening/...
1000 am update:

Pretty blustery day already out there today in the wake of a
powerful cyclone now making its way thru Quebec. West/northwest gusts
expected to increase a bit with more cloud breaks late in the
day. Until then, looking at more clouds than sun as Great Lakes-
enhanced shallow moisture on west-northwest 925-700 mb winds continues to
Foster periods of cold air stratocu. Winds have been gusting
pretty solidly in the 30 to 40 mph range, though into the
advisory range at Worcester. With cold advection and only peeks
of sun, look for temperatures to hover or only slowly rise a
couple degrees from current readings today, but the winds will
make it feel colder.

Prior discussion from earlier this morning:

* westerly wind gusts of 40 to 50 mph today.

Powerful low pressure dropping below 970 mb will continue to
lift northward through eastern Canada today. The resultant
pressure gradient along with steepening lapse rates with the
cold pool aloft will result in windy conditions today. BUFKIT
soundings continue to support 40 to 50 mph wind gusts across
much of the region. Therefore, wind advisories will continue for
most areas north of the CT/Rhode Island and Massachusetts border. We will come close
to meeting criteria across CT/Rhode Island too, but not confident enough
to extend southward at this time. Regardless, 40 to 50 mph wind
gusts expected today with the strongest across the high terrain
as well as as portions of the cape/islands.

Impressive cold pool aloft will result in a scattered to broken
deck of cloudiness, but still expect peeks of sunshine.
Westerly flow coupled with steep lapse rates and lake moisture
will result in scattered snow showers in the Berks. Across the
rest of our region, dry weather will dominate but a few passing
sprinkles/flurries can not be ruled out given the steep lapse
rates.

High temps will range from the upper 30s in the high terrain,
to the lower to middle 40s elsewhere. Although it will feel
colder given the windy conditions.

&&

Short term /6 PM this evening through 6 PM Monday/...
tonight...

The powerful low pressure system will lift further into
northern Canada and the pressure gradient begins to relax.
Westerly wind gusts of 35 to 45 mph are still possible into the
first half of the evening, but should see a downward trend
especially after midnight as a ridge of high pressure gradually
builds in from the west. Low temps are expected to drop into
the upper teens to middle 20s in most locations by daybreak
Monday in the cold air advection pattern.

Monday...

A ridge of high pressure over our region will keep US dry
during the day on Monday. We will see some mid level cloudiness
overspread the region in advance of low pressure lifting
northeast across the mid Atlantic. High temps will be colder
than today, remaining in the 30s but with much less wind than
today.

&&

Long term /Monday night through Saturday/...
highlights...

* confidence moderate to high for a plowable snow as well as icy
roads, Monday night through Tuesday, with the best chance across
interior Massachusetts/CT into northern Rhode Island. Impact to the Tuesday am commute
from snow, sleet and/or freezing rain. Details remain uncertain on
snow and ice accumulations which will depend upon the thermal
structure and precipitation type changes.

* Scattered snow showers from midday Wednesday into early evening
ahead of Arctic cold front, with some snow squalls possible.

* Temperatures fall to between 10 and 20 degrees below normal late
Wednesday night and Thursday with wind chill values from zero to
around -10 possible.

* Some gradual temperature moderation on Friday, but readings
remain below normal.

Details...

Monday night through Tuesday night:

** confidence continues to increase for winter weather
conditions Monday night through Tuesday **

Light west winds will linger across the region Monday night as
low pressure moves slowly east out of the Ohio and central
Appalachians. With a generally flat mid level flow, which will
start to tilt SW as a long wave trough digs across the central
and Western Plains, will see leading edge of light snow will
push S-north across CT/Rhode Island Monday evening.

Noting a classic cold dome of air lingering across the region
Mon night, while milder air will ride above it. This will allow
for mixed precip to start to work in late Monday night as the
precip lifts N-NE. Temps will start off in the mid 20s to mid
30s, coldest across the interior and higher terrain, then
transitions into a non-diurnal temp trend as readings slowly
rise overnight into Tuesday morning.

Still some uncertainty on the snow accumulations and especially
how much icing will be realized leadings into the Tuesday
morning commute. Looks like the best chances for freezing rain
and/or sleet will occur away from the immediate coast to start
the commute, then should change to rain by around mid to late
morning from around the Boston-Providence corridor southward to
the S coast. A wintry mix should continue through the afternoon
well inland, which could be the biggest impact especially across
untreated roadways and other outdoor surfaces.

As the low pushes S and east of Cape Cod and the islands late in
the day, should see a change back over to snow toward Tuesday
evening except across the S coast, Cape Cod and the islands.
Should see the precip taper off Tuesday evening, though snow
showers may linger across the east slopes of the Berkshires from
time to time overnight.

Current forecast suggests snow amounts on the order of less than
an inch along the S coast to around 2-4 inches from around the
Mass Pike northward, but still quite a bit of uncertainty on the
timing of the mixing and/or changeover to rain and how far that
will lift northward. Another issue will be the icing and its
impacts. Could see about 0.1 to 0.2 inches of ice across
portions of north CT, north Rhode Island into most areas of Massachusetts.

Headlines for at least advisory level conditions across the
interior remain possible (at least), but still questions on
placement of the ptypes and how long they will last overnight
into Tuesday.

Pretty confident for impacts across most roadways for the
Tuesday morning commute, especially areas near/north of Route 6
in CT and Rhode Island and near/northwest of I-95, and especially across from
Hartford to northwest of Providence to Boston and the interior southeast mass
areas. Coastal Massachusetts/Rhode Island into part of southeast Massachusetts should see a shorter
period of winter weather before changing to a cold rain.

Wednesday...

Will see mainly dry conditions except for some spotty snow
showers across the higher terrain and possibly across Cape Cod
and the islands. Another weak trough moves across which may
enhance some light snow showers elsewhere, but will be tough
with lack of moisture away from the higher terrain and near the
coastline. Something to keep an eye on, though.

Wednesday night into Thursday night...

Arctic airmass dives southeast across the region after the front passes
during early Wed night. Models continue to signal 850 mb temps
diving to -14c to -18c through the night. Light snow lingers
across Outer Cape cod and the island through around midnight
then should push offshore.

The coldest air of the season arrives Wed night and Thu. Lows
Wed night will bottom out in the single digits and teens, except
around 20s across Outer Cape cod and the islands. However, with
west-northwest winds at 10-20 mph, maybe a bit higher along the immediate
coast, could see wind chill values bottom out from -5 to -10
well inland and especially across the higher terrain to zero to
5 above along the coast by daybreak Thursday. May see some
dangerous wind chills especially for the children waiting for
buses out of doors. Bundle up!

As high pressure approaches Thursday, winds will diminish but
the cold air will remain in place. While temperatures moderate
some, it will remain cold though the wind chills will not be
quite as cold. Highs will be in the mid teens to around 20
inland and in the 20s across the coastal plain.

Friday and Saturday...

Large high pressure will dominate across the mid Atlc and
northeast both Friday and Saturday. It will remain cold on
Friday with highs in the 20s to around 30, though northwest winds
will be in the 5-10 mph range. Winds shift to north-NE but remain
light on Saturday with temps in the mid 20s and 30s with winds
veering to NE.

&&

Aviation /16z Sunday through Thursday/...
forecaster confidence levels...

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

Short term /through Monday/...

15z taf update:

Today...high confidence.

VFR with scattered-overcast stratocu (greater coverage west). Possibility
for a flurry from the stratocu layer but not expected to reduce
visbys. Strong west/west-northwest winds with 15-25 kt sustained winds, gusts
30 to 40 kts (tending highest on gusts toward the East Coast of Massachusetts
into the cape and islands).

Tonight...high confidence.

VFR conditions. West winds gusts diminish a bit, but still expect
many locations to gust between 25 and 35 knots through around
03z-05z.

Monday...high confidence.
VFR conditions despite some mid level cloudiness, especially
south of the mass Turnpike. West winds of 5 to 15 knots.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Monday night through Thursday/...

Monday night: MVFR/IFR conditions possible. Fzra, chance sn,
chance pl.

Tuesday: mainly IFR, with areas MVFR possible. Breezy. Ra, sn,
pl, freezing rain.

Tuesday night: mainly VFR, with local IFR possible. Breezy.
Slight chance snow.

Wednesday: VFR. Breezy.

Wednesday night through thursday: VFR. Windy with gusts up to
35 kt.

&&

Marine...
short term /through Monday/...

Today and tonight...high confidence.
Powerful storm across eastern Canada will continue to lift
north with the pressure dropping below 970 mb. The result will
be strong westerly gales. Gusts of 40 to 45 knots today and a
good portion of tonight. High pressure will begin to build in
from the southwest after midnight, which should allow winds to
gradually trend downward after that time. Seas 8 to 15 feet
across the outer waters today, gradually subsiding tonight.

Monday...high confidence. Lingering Small Craft Advisory wind gusts across the
eastern waters in the morning will diminish by afternoon as high
pressure builds over the waters. Seas will also subside, but
some 5 foot seas may linger across the eastern outer waters into
Mon afternoon.

Outlook /Monday night through Thursday/...

Monday night: winds less than 25 kt. Rain likely, freezing rain
likely, chance of snow. Local visibility 1 to 3 nm.

Tuesday: winds less than 25 kt. Local rough seas. Rain.

Tuesday night: low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft. Chance of rain. Local
visibility 1 to 3 nm.

Wednesday: low risk for Small Craft Advisory winds with gusts
up to 25 kt. Rough seas up to 9 ft. Slight chance of snow.
Areas of visibility 1 to 3 nm.

Wednesday night: strong winds with gusts up to 35 kt. Rough
seas up to 11 ft. Slight chance of snow. Visibility 1 to 3 nm.

Thursday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...Wind Advisory until 9 PM EST this evening for maz023-024.
Wind Advisory until 7 PM EST this evening for maz002>016-018-
019-021-022-026.
Rhode Island...Wind Advisory until 9 PM EST this evening for riz008.
Marine...Gale Warning until 1 am EST Monday for anz231>234-251-255-256.
Gale Warning until 10 PM EST this evening for anz230.
Gale Warning until 7 PM EST this evening for anz236.
Gale Warning until 11 PM EST this evening for anz235-237.
Gale Warning until 4 am EST Monday for anz250-254.

&&

$$
Synopsis...Frank/evt
near term...Frank/loconto/evt

National Weather Service Glossary of Abbreviations