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Dec 16-17 obs/nowcast thread


ORH_wxman
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21 minutes ago, DotRat_Wx said:

This band over BOS metro is nearly stationary and it's just pouring snow.. Will be getting into the double digits in no time. Crazy. 

It's crawling... so far not the same visibility and snowgrowth that we had 1:30am...  wonder what obs are south of the city where returns are better

 

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Area Forecast Discussion
National Weather Service Boston/Norton MA
425 AM EST Thu Dec 17 2020
.NEAR TERM /THROUGH TONIGHT/...
Winter storm continues to affect Southern New England early this
morning. Regional radar shows west to east oriented bands of heavy
snow, which have reportedly produced snowfall rates up to 2 inches
per hour at times, now beginning to lift north of the Mass Pike.
Water vapor imagery shows a dryslot on the southern end of the
cyclone`s 700 mb circulation (this feature over east-central PA),
and this dry slot is racing northeast from Long Island into a part
of southern CT/RI. In a nowcasting sense, this dryslot has led to
brief improvement in visibility (1/2 to 1 SM) across Hartford to
Willimantic CT to central/southern RI eastward into southeast MA,
with sleet at times mixing in. Speaking to temperatures, a coastal
front has set up from roughly Beverly to Norwood to North Smithfield
with ENE winds. Temps have been very slowly but steadily warming
east of this front; with most areas in Norfolk, Plymouth and Bristol
Counties hovering around 33-34F; upper 20s to around 30F into the
Boston area and up into the North Shore. More northerly winds in the
interior on the west side of the front has led to temperatures
commonly in the upper teens to low 20s!

We continue to have multiple weather-related concerns specific to
this winter storm. Accumulating snowfall is one of them. Rapidly
falling temperatures and a related flash freeze of snow/slush is
looking likely later this morning across South Shore into
southeastern MA. This may extend as far north as the Boston metro
area, potentially affecting I-95/Route 128 and the Southeast
Expressway. Strong northeast winds and minor coastal flooding are
other concerns.

Our surface low, a sub-1000 mb low just off the NJ coast, will
continue to pull NE into the waters near the Islands by late-
AM/early-PM, then move into the southern Gulf of Maine later in the
day today. The 700 mb cyclone will continue to progress eastward
into northern CT/western MA on into interior northern New England.

On the snow accumulation forecast: I`ve made only small
adjustments. The most significant of these changes was a
reduction in snow totals from Windham County CT ENE across much
of RI and into eastern and southeast MA by about 1-2". Much of
these same areas should still see values nearing 1 foot, but the
dryslot moving in may keep these areas from achieving foot-plus
levels. On the other side, I`ve boosted snow totals across
northwest and northern MA as deformation- zone banding on the
northern end of the 700 mb low now across eastern PA looks to
advance into these areas. Snow totals here were increased by a
couple inches, mainly north and west of a Springfield to
Worcester to Bedford line. Some of these areas from the east
slopes of the Berkshires into the Route 2 corridor may see
accumulations nearing 20". The forecast otherwise remains
essentially unchanged. For a large part of Southern New England,
snow intensity for today should be more of a steady light to
moderate intensity. The exceptions are for the aforementioned
northwest/northern MA area, with a secondary local maximum
hinted at by the 00z HREF, NAM and GFS across the North Shore,
Merrimack Valley into part of Metro Boston mid-morning into the
early afternoon. For this secondary area, I am thinking that
snow intensity may struggle to get to heavy levels especially by
late morning as moisture in the snow growth region becomes
unsaturated per NAM/RAP fcst soundings. Snow should taper off in
interior MA, CT and RI by around mid-day, and by mid afternoon
towards eastern MA. Periods of ocean effect snow showers may
continue to affect Cape Cod and parts of coastal Plymouth County
until evening, but the heaviest of the snows will have ended.

On the flash freeze potential: as winds flip to N and NW by mid to
late this morning, upper teens to mid 20s temperatures now in the
interior will surge southeast. This leads to the potential for a
rapid freeze-up of slush and snow, with highest confidence of this
occurring across Bristol, Plymouth and Norfolk Counties where
current temperatures are above freezing. Temps are very close to
freezing in Suffolk County/Boston area that there is the potential
for such even into Boston, but the better potential looks to be just
south.

On strong/gusty winds: High wind watch continues for the Islands
until 10 AM. It is still quite gusty out on the islands, but
damaging winds haven`t materialized. There may still be another
window of opportunity for gusts to increase. Gusts to 30-45 mph will
also continue across coastal MA, with gusts in the interior up to 30
mph. This will lead to blowing and drifting of snow.
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Good morning!  Slept just under 4 hours and from the 2nd floor snow looks deep-will measure shortly.  Snowing pretty good but I imagine 2-3 hours ago it must have been bombing to accumulate this quickly.  Let's see how much we can book-methinks almost everyone who stays all snow gets 12+.

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