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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
654 am EST Tue Nov 12 2019

Synopsis...

A strong cold front will sweep across the region this morning
into early afternoon with rain showers which will end as a
brief period of snow along with rapidly falling temperatures.
Record cold along with windy conditions follow tonight into
Wednesday. Temperatures begin to moderate on Thursday, but will
still be below normal for the middle of November. Even milder
weather is on tap for Friday, but that will be short lived as a
cold front Ushers in a return to well below normal temperatures
later Friday night and Saturday. We then will have to watch an
offshore storm early next week, but it remains uncertain if it
will impact our region. Temperatures should moderate some early
next week.

&&

Near term /until 6 PM this evening/...

650 am update...

Main issue early this morning is shallow cold air that has
brought temps down to around freezing across far north central
and northeast Massachusetts. The concern is roughly from Fitchburg, to
Lawrence, to Amesbury near the New Hampshire border. Patchy fog and spotty
light rain may freeze on some untreated roadways near the New Hampshire
border through mid morning.

Otherwise, focus continues to be rain that changes to a very
brief period of of snow from west to east later this morning
into early this evening. Overall, thinking a rather limited
impact with short-duration of snow and marginal temps. Coating to
perhaps up to an inch with best chance for those amounts in the high
terrain. Perhaps a few slippery spots, but overall think this is
a low impact.

Ana-frontal wave lifts NE across interior new eng this morning
with the attending cold front sweeping across the region
12-18z. After the front moves through, about a 3-6 hour period
of precip is expected to overspread southern New England through the morning
reaching the cape/islands this afternoon as deep moisture axis
combines with decent low level frontogenesis. Initially the
precip will be rain but will end as a brief period of snow as
colder moves in from top down. Some sleet is possible during the
transition. Timing of the changeover will be 14-17z from west
to east in western/central Massachusetts and northern CT, 18-21z across Rhode Island
and eastern Massachusetts and 21-00z cape/islands. Quantitative precipitation forecast in the cold air is
light and so only expecting a coating to perhaps an inch in some
locations, especially over the higher terrain.

Wide range in temps early this morning, ranging from lower 30s
near the New Hampshire border to near 60 on Cape Cod which is south of the
warm front. Highs reaching upper 50s to lower 60s late this morning
across far Rhode Island and far southeast Massachusetts and cape/islands but falling sharply
through the 30s this afternoon. A dramatic temp drop will be
felt this afternoon across southeast new eng, potentially up to a 30
degree drop in 6 hours. Elsewhere, feel 3 km NAM is correct
that shallow cold air will hang tough and be followed by the
cold front. Highs stay in the 30s to near 40, with falling temps
into the 20s over the higher terrain and near freezing elsewhere
during the afternoon. Strong cold advection will result in
Post-frontal northwest wind gusts increasing to 25-35
mph this afternoon.

&&

Short term /6 PM this evening through 6 PM Wednesday/...

*** record cold and bitter cold wind chills late tonight and Wed
morning

The last of the rain/snow exits the Outer Cape/islands early
evening, otherwise clearing skies tonight with mostly sunny
skies Wed. The main story will be the bitter cold airmass for
mid November which will advect across new eng on gusty northwest winds.
Gusts to 30-40 mph expected tonight with gradually diminishing
wind during Wed, especially in the afternoon.

925 mb temps down to near -15c by 12z Wed. Lows will drop into
the teens with some single numbers possible in the Berkshires
which will be near record lows. High on Wed only mid 20s to
lower 30s which would establish record low maxes at all 4
climate sites. Wind chills will bottom out between 5 below and
5 above across much of southern New England late tonight and early Wed.

&&

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



* near record cold again Wed night, but with light winds

* moderating temps Thu, but still below normal

* seasonable temps briefly return Fri, but turning cold again by Sat

* watching offshore storm late sun into Tue with moderating temps

Details...

Wednesday night...

Large high pressure will be centered over New England with an
anomalously cold airmass in place. This combined with light winds
will result in the potential for near record low temps. The only
thing that may temper things a bit will be some mid/high level
cloudiness that will overspread the region. Model cross sections do
show this risk, so something will have to watch.

Right now we are thinking lows bottom out between 5 and 10 above
across the normally coldest outlying locations, to mainly the teens
elsewhere. The urban heat island of Boston probably does not drop
below 20. So a wide range in overnight low temps across the region,
but without the wind it will not feel as harsh as tonight will be.

Thursday and Thursday night...

High pressure moving off the coast will allow a return flow of
milder southwest air to work into the region. Afternoon high temps
should recover into the upper 30s and lower 40s. While those
readings are still below normal, it will be a significant improvement
compared to Wednesday along with much less wind.

We expect a fair amount of clouds to develop Thu, but peeks of
sunshine too especially in the morning. Deep moisture and synoptic
scale forcing is lacking, so perhaps just a few brief spot rain
showers near southeast New England coast by Thu night. Boundary
layer will be mild enough in that region that any spotty/light
precipitation should be liquid.

Friday...

High pressure east of our region along with an approaching cold
front will continue to result in southwest flow and milder temps.
Mainly dry weather with expected highs to reach the upper 40s to the
lower 50s.

Friday night and Saturday...

A strong cold front will cross the region Fri night. Very little
moisture is available, so should come through dry other than perhaps
a brief flurry/snow shower in western Massachusetts. The main story will be
another shot of unseasonably cold air. Although the 850t probably
will not get as cold as our airmass late tonight and Wednesday, the
cold air will be coming in from more of a northerly direction with a
1037 mb high in Quebec. This is a good feed for New England, so it
should turn much colder. Highs on Sat will only be in the 30s. May
even have to watch for a bit of ocean effect light snow
showers/flurries across the cape/ack with northerly winds Sat into
Sat night.

Sunday through Tuesday...

A great deal of forecast uncertainty exists in this time frame. The
upper level trough over the northeast begins to relax, but will be
watching southern stream energy that will lead to the development of
an ocean storm. Not sure how much interaction it will have with
northern stream energy. So it remains uncertain if most of the
precipitation remains offshore or ends up impacting much of our
region. If we do end up getting impacted early next week, ptype
would probably favor rain given modifying airmass. Still would have
to watch for a bit of snow/ice across the interior if precip were to
come in on the earlier side. Not much more to say at this point,
but do expect temps to moderate some early next week.

&&

Aviation /12z Tuesday through Saturday/...

Forecaster confidence levels...

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

Short term /through Wednesday/...moderate confidence.



Today...moderate confidence.

Wide variety of conditions early this morning with fog and low
clouds generally north of a bdl...to pvd...to tan line. IFR-
LIFR conditions may hang tough northwest of a pvd to tan area
given shallow cold air. May have to wait until later this
morning/early afternoon as winds shift to northwest for improvement to
MVFR-VFR thresholds.

Rain overspreads the region from west to east through the
morning into early afternoon. Changes to a very brief period of
snow before exiting the far southeast New England coast early
this evening. Minor accums, mostly less than 1 inch possible,
especially over higher elevations. Conditions improving to VFR
from west to east during the afternoon and evening. Wind shift
to northwest with gusts 25-30 kt developing in the afternoon.

Tonight...high confidence.
Lingering MVFR cape/islands early, otherwise VFR with clearing
skies. Northwest gusts 25-30 kt.

Wednesday...high confidence.
VFR. Gusty northwest winds in the morning, diminishing in the
afternoon.

Kbos terminal...moderate confidence in taf.

Kbdl terminal...moderate confidence in taf.

Outlook /Wednesday night through Saturday/...

Wednesday night: VFR. Breezy.

Thursday through Thursday night: mainly VFR, with local MVFR
possible. Breezy.

Friday: VFR. Breezy.

Friday night through saturday: VFR. Strong winds with local
gusts up to 40 kt.

&&

Marine...
short term /through Wednesday/...high confidence.

SW gusts to 25-30 kt over south coastal waters this morning,
then wind shift to northwest this afternoon with increasing winds all
waters. Gusts peaking at 35-40 kt tonight with gradually
diminishing wind during Wed. Gales on all waters. Visibility
restrictions in rain and fog especially this afternoon.

Outlook /Wednesday night through Saturday/...

Wednesday night: winds less than 25 kt. Local rough seas.

Thursday: winds less than 25 kt.

Thursday night: low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
rain showers.

Friday: low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Slight chance of rain showers.

Friday night: moderate risk for gale force winds with gusts up
to 40 kt. Areas of rough seas.

Saturday: moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 12 ft.

&&

Climate...
record low min temps for Wednesday Nov 13

Boston 14/1883
Hartford 18/2001
Providence 20/2001
Worcester 15/1986

Record low Max temps for Wednesday Nov 13

Boston 36/1874
Hartford 33/1911
Providence 37/1911
Worcester 32/1962,2013

Record low min temps for Thursday Nov 14

Boston 16/1905
Hartford 15/1986
Providence 16/1905
Worcester 10/1986

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Gale Warning from 4 PM this afternoon to 1 PM EST Wednesday
for anz231>235-237-250-251-254>256.
Gale Warning from 7 PM this evening to 7 am EST Wednesday for
anz230-236.

&&

$$
Synopsis...kjc/Frank
near term...Frank/kjc
short term...kjc

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