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000
FXUS61 KBOX 212352
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
652 PM EST Mon Jan 21 2019

.SYNOPSIS...
Arctic airmass and dangerously cold wind chills continue into
tonight with moderating temperatures Tuesday. Much milder air
moves in Wednesday into Thursday. An approaching frontal system
will bring occasional rain Wednesday afternoon into Wednesday
night with a period of heavy rain possible on Thursday. Mainly
dry and more seasonable temperatures Friday then turning much
colder Saturday. Snow showers are possible Sunday as another
front approaches.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
650 PM update...

Scattered flurries/snow showers associated with deeper moisture
plume and mid level warm advection rotating across eastern MA.
This moisture will move offshore by midnight with clearing skies
developing. Exception will be over the outer Cape where
occasional ocean effect snow showers will persist. Temps will be
steady or even rise a few degrees tonight as wind continues and
CAA stops as core of coldest air aloft exits. However,
dangerously cold wind chills continue. Current forecast on
track.

Previous discussion...

*** Wind Chill Headlines Continue ***
*** Lows 5 above to 5 below zero ***

Mid level vortex that delivered the arctic airmass to the region
is now located over eastern New England. Warmer air aloft
(TROWAL) is beginning to wrap around the system cyclonically
into southern New England. This is resulting in lots of clouds
and some flurries/light snow from time to time across the area.
Not expecting any accumulation other than a possible dusting or
coating.

Any accumulating snow tonight will be confined to the outer Cape
from Provincetown to Chatham as WNW winds veer to the NNW,
providing a longer fetch. This will result more persistent ocean
effect snow showers across the outer Cape. Hi res guidance
offering up to 0.15 qpf thru tonight. Snow ratios not ideal as
it`s too cold with temps below -20C. Thus not looking at
dendrites but more snow grains and/or needles. Nevertheless
expecting a coating to 2 inches for most locations between
Provincetown to Chatham. Low risk of up to 3" in a few
locations. Hyannis westward very little if any snow accums given
NNW trajectory.

Another frigid night ahead along with a very cold start here as
sunset approaches. Not as much of a temp drop tonight given core
of cold air at 850 mb and 925 mb is centered over the region at
the moment. Thus CAA eases tonight and not expecting radiational
cooling as gusty NW winds persist. Nonetheless forecasting lows
from 5 above to 5 below for the most part along with wind chills
from -15 to -25 for much of the area. Therefore wind chill
advisories.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
4 PM update...

Tuesday...

Frigid again tomorrow morning along with bitterly cold wind
chills. However not nearly as cold as today especially during
the afternoon as airmass modifies and winds slacken in response
to high pressure building in from the west. Highs actually
manage to get into the low and mid 20s along with sunshine.

Tuesday night...

With high pressure overhead and a very dry airmass in place
temps will freefall during the evening. Therefore followed the
colder MOS temps. Expect temps to level off second half of the
night as SSW pgrad increases along with mid/high clouds
approaching from the west.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Highlights...

* Rain Wed aftn/night possible starting as snow/mixed precip interior
* A period of heavy rain Thu, especially SE New Eng
* Mainly dry and turning colder Fri into Sat
* Snow showers possible next Sunday

Wednesday...

Increasing warm advection in SW flow combined with deepening
moisture plume moving into SNE will bring rain to SNE, mainly
during Wed afternoon. The column is marginally cold enough for some
snow/sleet at the onset across the interior, but this should be
short lived as increasing SW flow rapidly warms the boundary layer.
Temps moderate into the upper 30s to mid 40s during the afternoon.
Modest low level jet develops across the coastal plain and soundings
show enough BL mixing to support gusts to 35 mph SE New Eng.

Wednesday night into Thursday...

Good heavy rain signal late Wed night/Thu as low level jet advects
anomalous PWATs into SNE. PWAT and low level wind anomalies are 3SD
above normal. Widespread rain expected Wed night with heaviest rain
likely during Thu as axis of low level jet and frontal wave enhances
convergence along the boundary. Some elevated instability so
also can`t rule out some convection across SE New Eng. Expect
widespread rainfall 1 to 2 inches, with risk of localized 3 inch
amounts across RI and SE MA which will result in areas of urban
and poor drainage flooding. 70-80 kt low level jet develops across
SE New Eng on Thu. Soundings show a good low level inversion which
will limit these gusts from reaching the surface but still potential
for gusts reaching advisory criteria across SE New Eng.

Friday into Sunday...

Deep trough sets up across eastern Canada as piece of polar vortex
rotates south from Hudson Bay with dominant northern stream across
New Eng. Blustery and seasonably cold Fri, then secondary front
delivers modified arctic air for Fri night/Sat with below normal
temps. Mainly dry Fri/Sat although some higher elevation flurries
possible at times as series of shortwaves rotate through. Higher
risk of snow showers Sunday associated with a stronger shortwave
and more moisture as onshore flow develops.

Monday...

Low confidence given lots of spread in upper air pattern. Followed
WPC guidance with continued chance of snow/rain showers.

&&

.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/...High confidence

7 PM update...

Tonight...

Scattered snow showers and localized MVFR across eastern MA will
end after 02z with partial clearing and VFR. Otherwise, MVFR
should be confined to the outer Cape in snow showers with snow
accumulations ranging from a coating to 2 inches. Elsewhere VFR
with gusty WNW winds becoming more NNW with gusts up to 30 kt,
highest over the Cape and Islands.

Tuesday....

MVFR cigs continue across the outer Cape. Otherwise VFR prevails
along with NNW winds 20-30 kt.

Tuesday night...

Winds finally diminish. VFR with low risk of MVFR and precip
exiting eastern NY into western New England. Brief period of a
wintry mix possible but likely holding off until Wednesday.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF

Outlook /Wednesday through Saturday/...

Wednesday: MVFR/IFR conditions possible. Windy with gusts to
30 kt. Chance RA, FZRA.

Wednesday Night: Mainly MVFR, with areas IFR possible. Windy
with gusts to 35 kt. RA.

Thursday: Mainly MVFR, with areas IFR possible. Strong winds
with areas gusts to 45 kt. RA, chance FZRA.

Thursday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance SHRA, slight chance SHSN.

Friday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHSN.

Friday Night: VFR. Breezy.

Saturday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

4 PM update...

*** Heavy Freezing Spray Warning ***
*** Gale Warnings Continue ***

Tonight...

Frigid airmass continues to overspread the waters via WNW gales
that become NNW overnight. Heavy freezing spray warning eastern
MA waters, freezing spray advisory elsewhere. Snow showers limit
vsby to about 1 mile at times.

Tuesday...

NNW gales likely in the morning along with moderate to heavy
freezing spray. But improving during the afternoon as temps not
as cold and wind eases as well.

Tuesday night...

Light winds as high pres builds over the waters. No headlines
expected.

Outlook /Wednesday through Saturday/...

Wednesday: Low risk for gale force winds with gusts up to
35 kt. Areas of rough seas. Chance of rain.

Wednesday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 11 ft. Rain likely.

Thursday: Moderate risk for gale force winds with gusts up to
45 kt. Rough seas up to 15 ft. Rain.

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Rough seas up to 14 ft. Chance of rain
showers.

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 11 ft.

Friday Night: Winds less than 25 kt. Rough seas up to 9 ft.

Saturday: Winds less than 25 kt. Areas of rough seas.

&&

.CLIMATE...
RECORD LOW MAX TEMPERATURES TODAY/MONDAY....

Boston ...        12 ... 1985
Providence ...     7 ... 1985
Hartford (BDL) ... 8 ... 1985
Worcester      ... 8 ... 1985

As of 4 pm here are the observed high temps today...

Boston...7
Providence...5
BDL...4
Worcester...-2

These numbers will be updated between 430-5pm when our climate
summaries are issued.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Chill Advisory until 8 AM EST Tuesday for CTZ002>004.
MA...Wind Chill Advisory until 8 AM EST Tuesday for MAZ003>007-
     010>021-026.
     Wind Chill Warning until 5 AM EST Tuesday for MAZ002-008-009.
RI...Wind Chill Advisory until 8 AM EST Tuesday for RIZ001>007.
MARINE...Heavy Freezing Spray Warning until 6 AM EST Tuesday for ANZ231-
     232-250-251-254.
     Gale Warning until 7 AM EST Tuesday for ANZ230>237-251.
     Freezing Spray Advisory until 11 AM EST Tuesday for ANZ233>235-
     237-255-256.
     Gale Warning until 2 PM EST Tuesday for ANZ250-254>256.

&&

$$
SYNOPSIS...KJC/Nocera
NEAR TERM...KJC/Nocera
SHORT TERM...Nocera
LONG TERM...KJC
AVIATION...KJC/Nocera
MARINE...KJC/Nocera
CLIMATE...