FXUS61 KBOX 180019

Area Forecast Discussion
National Weather Service Boston/Norton MA
719 PM EST Sat Nov 17 2018

Diminishing W winds as high pressure shifts across the region
into Sunday. Expect unsettled conditions Sunday night through
Monday as weak low pressure moves across, bringing periods of
light rain and/or snow. More cold air will move in by mid week
into Thanksgiving, though it should remain dry. Cold air could
be near or record breaking for late November.


No major changes to the ongoing forecast overnight. Latest
satellite data showed an abundance of clouds across southern New
England, with a few breaks, mainly across eastern CT, RI and
portions of eastern MA. Expecting more clearing across the
eastern half of southern New England towards midnight. More
clouds should arrive from the west late tonight. Adjusted
forecast over the next several hours to reflect observed trends.


A cold, dry night. Not considerably cold, believe a few factors will
limit boundary layer decoupling and radiational cooling. For one, W
winds still breezy around 5-10 mph. Two, scattered to broken cloud
decks beneath prevailing broad cyclonic flow. And lastly, snowmelt
and high dewpoint air round the upper 20s to low 30s at max heating
of the day. Not a clear-cut case of radiating down into the teens,
rather forecasting widespread mid-upper 20s with coastline and lower
CT River Valley around 30. Can't rule an isolated locale decoupling,
especially if with deep snowpack, seeing lows closer to 20 degrees.
Again, chilly, dry, with any wind, making it feel 5 degrees cooler.


A dry start much of Sunday, but a weak weather disturbance sweeping
through Sunday night into Monday. Light outcomes with the potential
for a sub-advisory, trace up to 2 inches of snow, especially over
N/W portions of MA and CT, highest amounts across the high terrain.
Otherwise light rain. Potential Monday AM commute impacts.

Weak, stretched mid-level shortwave impulse through broader cyclonic
flow. Streaming moist-continental H6-9 airmass undergoing isentropic
ascent along 285-295K surfaces, aided via orographic lift along high
terrain. Outcomes along a fairly diffuse low center with ill-defined
boundaries, tandem subtle increasing thicknesses, however remaining
cold enough for snow over N/W MA and CT. Support via a neighboring
jet-streak downstream, some RRQ influences, a thermal wind response
that extends down to H925-85 yielding a convergent nose of the low-
level jet out ahead of the diffuse low center.

Notable model spread. In general, global forecast guidance broader
with outcomes, stronger lift and ascent parameters, whereas high-res
forecast guidance is weaker, blotchy, more focused over high terrain
where lift is best. Consensus speaking, H8-9 frontogenesis noted
with convergent low-level jet nose, as is the moist-continental H6-9
airmass, ice within the column, and conditionally unstable profiles
through the snow-growth region upon which to act upon. Anti-cyclonic
ascent likely but the depth and magnitude of which remain uncertain.
Overall, a weak event forecast models are likely having difficulty
defining, but rain / snow outcomes appear likely.

Model forecast snow probabilities focused over N/W MA and CT. Though
spread exists within model forecast plume diagrams with respect to
liquid-equivalent precipitation. Favoring a consensus blend approach
with available guidance, especially WPC / NERFC forecasts, working
with other forecast offices. Sub-advisory event with a trace to
2 inches over N/W areas of MA and CT, especially the high terrain.
Kicking off as early as late afternoon Sunday, however the bulk
of the outcomes centered around midnight into early Monday morning.

Some potential Monday AM commute outcomes especially along the Route-2
corridor and western portions of I-90 with roads becoming snow covered
making for slick, hazardous travel as snow accumulation is expected
on all surfaces. Also expected reductions in visibility.



* High pressure brings dry and cold conditions for Wed through
Thanksgiving Day
* Signs a potential warm up late next week into next weekend


Generally looking at a broad mid level trough lingering over the
Northeast through at least Thanksgiving day. Modest ridging is then
expected late next week into next weekend. General agreement with
this overall pattern among the 17/12Z guidance. Some detail
differences with the timing through the upcoming week, which is not
uncommon. Will favor a consensus approach to smooth over the less
predictable details.


The majority of this period will most likely feature below normal
temperatures. Thanksgiving looks to be the coldest period, with a
strong signal of 2-3 standard deviations below normal. High
temperatures expected to struggle to reach freezing. Modest warmup
late next week, but not a guarantee.


Looking like a busy first half of next week. Complicated pattern as
a low pressure moves into the Great Lakes Monday night, then
possible transfers some energy into a coastal low pressure off the
Mid Atlantic coast Tuesday. Between these two, there is a risk for
some rain and/or snow. It will all hinge on the timing details, the
more this event occurs at night, the more probable accumulating snow
will be in the forecast.

Mainly dry weather expected Wednesday through Saturday. Based on
current temperature forecast, there is the possibility for some
ocean effect snow across the outer Cape and Nantucket Wednesday
night into Thursday.


Forecaster Confidence Levels...

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

Short Term /through Monday/...High Confidence.

VFR continues. Breezy W/NW winds 10 to 20 kts, lower across the
interior. Continued CIGs 3-4 kft becoming more SCT, especially

Remaining VFR however CIGs thickening and lowering towards evening.
Potential MVFR across the high terrain by 0z with possible -RA/-SN
beginning. Winds shifting S/SW through the day.

Sunday night through Monday...
MVFR-IFR mix with widespread -RA/-SN. Wintry outcomes more NW versus
wet weather outcomes SE. Lower VSBYs with -SN. S/SW flow becoming
W/NW towards Monday evening.

KBOS Terminal...
No impacts through 0z Monday. VFR. After 0z Monday, lowering MVFR
to IFR, -RA moving into the terminal overnight and continuing
through the Monday AM push.

KBDL Terminal...
No impacts through 0z Monday. VFR. After 0z Monday, lowering MVFR
IFR, -SN forecast overnight into Monday morning mixing with -RA,
impacts to the Morning AM push.

Outlook /Monday Night through Thursday/...

Monday Night: VFR. Chance SHSN and SHRA. Patchy BR.

Tuesday: Mainly VFR, with local MVFR possible. Slight chance

Tuesday Night through Wednesday Night: VFR. Breezy.

Thanksgiving Day: VFR. Windy with local gusts to 30 kt.


Forecaster Confidence Levels...

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

Short Term /through Monday/...High confidence.

Small Craft Advisories concluding as W winds continue to
diminish. Waves dampening.

Good boating weather as both winds and seas will be light. Will
see W winds turn S/SW through the day. Increasing clouds out of
the SW, lowering and thickening ahead of the next weather system
with the threat of some rain Sunday night into Monday.

Sunday night into Monday...
Rain overspreading the waters as S/SW flow continues. Gusts up
to 20 kts. No hazards forecast for boaters but there could be
some reductions in visibility due to the rain which is expected
to be light. Winds shifting W/NW by Monday evening.

Outlook /Monday Night through Thursday/...

Monday Night: Winds less than 25 kt. Chance of rain showers.

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft.

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft.

Thanksgiving Day: Moderate risk for Small Craft Advisory winds
with areas of gusts up to 30 kt. Local rough seas.


MARINE...Small Craft Advisory until 4 AM EST Sunday for ANZ250-254-255.
Small Craft Advisory until 1 AM EST Sunday for ANZ251-256.


NEAR TERM...Belk/Sipprell
SHORT TERM...Sipprell
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