Gale Watch 4, NWS Boston/Norton, MA

Area Forecast Discussion
National Weather Service Boston/Norton MA
356 AM EST Fri Jan 10 2020

.SYNOPSIS...
High pressure off the east coast will draw milder air north into
Southern New England. Mild and breezy weather continues into
Saturday. A cold front brings showers and possible thunderstorms
Saturday night into Sunday, followed by cooler and drier weather
early next week, although temperatures should still average
above normal. Rain or snow showers may return for mid week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
South to southwest winds will bring milder air to the region,
bringing higher max temperatures than yesterday. The warm
advection will limit the depth of any mixing. Temperatures at
950 mb support highs in the 40s, and at 925 mb they support
upper 40s and lower 50s. This suggests max temperatures today in
the 40s and around 50.

Winds in the lower levels will also be increasing today, with 40
kt forecast at 950 mb and 50 kt at 925 mb. In a WAA pattern, 925
mb be be a bit high for mixing, but mixing should be sufficient
to bring 30-35 kt gusts during the afternoon.

A weak front will move into Northern New England this afternoon.
Showers along the front could reach far northern or western MA,
but the more favorable are will be to the north and west of MA,
closer to the front.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tonight...

Leftover showers will again be mostly favored to our north but
could reach some adjoining areas of Massachusetts. Will allow
for low-end chance pops in Western and Central MA and Northern
CT. Most areas will be dry.

Low level winds aloft will maintain 40-50 kt, with potential for
southwest wind gusts 30-35 kt at the surface. Mixing of this
wind to the surface will be more difficult, which is why the
expected wind gusts will be lower than the winds aloft.

Warm advection will continue through the night, so temperatures
will be at their lowest early in the night, with steady or
slowly rising values through the night.

Saturday...

A cold front moves from Canada into Northern New England, then
stalls well to our north. Southern New England will be on the
warm side of this system, but also far enough away to limit the
affect of showers. Most of the showers will be in NY and
Northern New England. Will continue to advertise low-end pops
for showers, mainly in Western and Central MA and Northern CT.

The warm advection means another mild day. Temps at 950 mb
support max temps in the lower 60s. This would be at or near
record levels...see the Climate section later in this
discussion.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights...

* Record warmth possible Sat night/Sun with showers/few storms
* Potential for minor flooding on mainstem CT River early next week

Subtropical ridge continues to be dominant feature across eastern
third of country into early next week keeping upper heights well
above normal for the middle of January. Eventually the ridge becomes
suppressed to Gulf Coast which allows southern stream energy to
rotate through New England, but heights remain above normal through
end of work week.

Main concern for impactful weather is with cold front Saturday night
into Sunday. An anomalously warm airmass remains in place ahead of
front with potential for record warm low temps Saturday night and
record highs early Sunday. Models show strong low level moisture
convergence on nose of 70+kt low level jet developing ahead of front
along with larger scale lift from upper trough rotating through
eastern Great Lakes.

Expect to see band of showers with embedded thunder cross SNE later
Saturday night into early Sunday morning as there is sufficient
MUCAPE (up to 100 J/kg) forecast for most of region. Due to very
strong winds aloft, especially near South Coast, will need to keep
an eye on any convective elements for possible localized damaging
wind gusts (low chance right now). Otherwise, forecast soundings in
pre-frontal airmass are strongly inverted which will limit mixing
potential, but gusts should still reach 45 mph along coast
(especially around Cape Cod and Islands). Doesn't look like classic
setup for high winds (>58 mph) with SW flow but we will probably
need Wind Advisories for these areas. Gale Watches are being issued
for south coastal waters.

Regarding rainfall, despite anomalous PWATS near 1.50" and deeply
saturated layer above freezing which supports warm rain processes,
speed of system should limit totals from becoming excessive.
Ensembles and 00z deterministic models are in good agreement with
anywhere from 0.25 to 0.75", most of which falls with the frontal
band of showers/embedded storms. While locally higher totals are
certainly possible, basin averages should be low enough to preclude
a significant threat of flooding. That said, there is a greater
potential for minor river flooding along mainstem Connecticut River
early next week (Mon-Tue) as seen in MMEFS due to snowmelt and
heavier rainfall in the headwaters across northern New England.

Drier and somewhat cooler weather follows Monday and Tuesday,
although temperatures should still remain above average. Weak system
may bring few rain or snow showers Tuesday night into early
Wednesday, then we are seeing better agreement that next southern
stream system will track into eastern Great Lakes. Pattern still
looks more wet than white, but if we see secondary low development
near triple point over SNE, that would result in somewhat colder
(rain/interior mix or snow) scenario.

&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Moderate to high confidence.

Today...

VFR cloud bases for much of the day. Eventual MVFR ceilings
develop toward evening. Increasing south to southwest winds with
gusts to 30 kt. Southwest winds above the surface will reach
40-50 kt, which may generate low-level wind shear late in the
day.

Tonight...

MVFR cigs, with widely scattered MVFR vsbys in showers in
Western and Central MA. Spotty IFR in the higher elevations
such as the Berkshire East Slopes and the Central Hills.

Saturday...

MVFR ceilings, with VFR developing in the coastal plain in the
afternoon. Windy with southwest gusts 30 to 35 kt. Areas of low
level wind shear with southwest winds at 2000 feet AGL 40-50 kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Mainly VFR, with areas MVFR possible. Windy
with gusts up to 35 kt. SHRA likely, chance TSRA.

Sunday: Mainly VFR, with local MVFR possible. Strong winds with
local gusts up to 40 kt. Chance SHRA.

Sunday Night: VFR. Breezy.

Monday through Monday Night: VFR.

Tuesday: VFR. Slight chance SHRA, slight chance SHSN.

&&

.MARINE...
Confidence is moderate to high.

Gale Watch on the eastern outer waters will be converted to a
Gale Warning for today and early tonight.

Today...

Increasing south to southwest winds today. Strong winds about
2000-3000 ft above the surface with speeds of 40 to 50 kt. This
will bring gusts to 30 kt most waters and 35 kt on the eastern
outer waters. Seas build to 5-8 feet, highest on the eastern
waters. Gale Warning on the eastern outer waters, with Small
Crafts on all other waters.

Tonight...

Winds diminish a little tonight, but expect winds at 25 kt and
seas 5-8 feet on all exposed waters. Small Craft Advisory on all
waters. Gales in the east subside to SCA.

Saturday...

Winds aloft remain at 45-55 knots, showing potential for at
least 30 kt gusts in the southwest flow. This will continue to
support seas of 5-9 feet.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 13 ft. Rain showers likely, chance of
thunderstorms.

Sunday: Low risk for gale force winds with gusts up to 40 kt.
Rough seas up to 15 ft. Rain showers likely, chance of
thunderstorms.

Sunday Night: Winds less than 25 kt. Rough seas up to 11 ft.

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

Monday Night: Winds less than 25 kt. Seas up to 5 ft.

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.

&&

.CLIMATE...
Record warmest lows for Saturday Jan 11th...

BOS 45/1983
ORH 37/1972, 1983 and 2017
BDL 41/1924
PVD 43/1924

Record highs for Saturday Jan 11th ...

BOS 62/1975
ORH 58/1924
BDL 60/1983
PVD 61/1975

Record highs for Sunday Jan 12th...

BOS 61/1913, 1975 and 2017
ORH 59/2018
BDL 60/2018
PVD 62/2018

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from late Saturday night through Sunday afternoon
     for ANZ231>235-237-255-256.
     Small Craft Advisory until 4 AM EST Saturday for ANZ231>234-
     251.
     Small Craft Advisory until 11 PM EST this evening for ANZ230-
     236.
     Small Craft Advisory until 8 AM EST Saturday for ANZ235-237-
     255-256.
     Gale Warning until 9 PM EST this evening for ANZ250-254.

&&

SYNOPSIS...WTB/JWD
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...JWD
AVIATION...WTB/JWD
MARINE...WTB/JWD
CLIMATE...Staff

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