NWS Boston/Norton, MA wrote its last area forecast discussion before the first event at Jan 13, 7:09 AM EST, 1 hour 50 minutes earlier.
Area forecast discussion, Jan 13, 7:09 AM EST, 1 hour 50 minutes before
Area Forecast Discussion
National Weather Service Taunton MA
709 AM EST Sat Jan 13 2018
.SYNOPSIS...
Heavy rain ends this morning as a bit of ice across western MA with
a flash freeze the main story across the rest of the region as
temperatures crash today. Mainly dry but very cold weather follows
tonight through Monday. Mainly dry but cold weather is expected
Sunday and Monday. Low pressure diving south from the Canadian
Arctic will bring a chance of snow Tuesday and Wednesday. Dry
weather may return Thursday and Friday. We will be watching a
potential coastal storm that could change that Thursday
forecast.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
***Heavy Rain/Urban Street Flooding Threat Ends By Mid Morning***
***A bit of ice across western MA this morning but the main story
will be a flash freeze today as temperatures crash***
7AM update...
Meso-low pres already shifting through the area with strong dry
slot apparent on lower lvl WV. Therefore widespread rainfall
should be ending over the next hour or so with a few spots of
drizzle and fog developing until winds can shift around to the
W.
Speaking of this change, cold front has remained dammed against
the Berkshires now for some time, so timing of of the cold
fropa, freeze and rapid shift to the W has been slowed
continually this morning, and will continue this trend based on
newest data available. Will maintain the the winter wx advisory
however, because once the cold air filters E, there should
remain a fair amount of standing water to freeze rapidly.
Previous discussion regarding this follow...
Western MA Light Icing With Flash Freeze The Main Story Today:
Temperatures were mainly in the upper 50s to the lower 60s very
early this morning...but have dropped into the 30s along the east
slopes of the Berks early this morning behind a very strong cold
front. This cold front will cross western MA by 12z...reach the
Boston to Providence corridor by 15 or 16z and then off the
southeast New England coast by 18z. Enough precipitation will
remain for a brief period of light freezing rain/sleet across
western MA. For the rest of the region...the cold air
should come in pretty much after the precipitation has ended.
However...may still see an hour or two of spotty -fzdz as the surge
of cold air initially comes in shallow and there is some left over
low level moisture for a 1 to 3 hour period.
The main concern though is the expected Flash Freeze and dramatic
drop in temperatures today. Most of our flash freezes occur when
our winds turn north northeast which prevent drying. In this
case...the winds will turn northwest which should allow for at least
some drying. However...given the dramatic temperature drop from
readings in the upper 50s to lower 60s very early this morning and
into the 20s in most locations by mid afternoon is quite unusual in
this part of the country. Given all the recent rain/street
flooding/standing water think will see some icing issues and will
continue the winter weather advisory along and northwest of the
Boston to Providence corridor.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Tonight...
Very cold air will be ushered in on north to northwest winds.
Although we won/t be extremely cold at 850 mb this airmass will come
down shallow and expect overnight low temps to mainly be in the
single digits to lower teens in most locations. We may even flirt
with wind chill advisory conditions along the east slopes
of the Berks...but it was too marginal to issue at this time.
Meanwhile on the outer-Cape...NNW winds may allow
for some ocean effect snow showers to develop overnight but with
accums of only a dusting to less than 1 inch are expected.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
Highlights...
- Cool and mainly dry except light snow across extreme SE MA.
- Advisory or even winter storm snow possible Tue into early
Thu depending on track.
- Seasonable late week.
Overview and model preferences...
The formation of an upstream Rex-block, signaling a strong
positive PNA, combined with blocking cutoff high pres at H5
near the Azores, allows meandering cutoff to settle near the
Great Lakes early in the week. This is a PV lobe associated with
a current Baffin Island vortex, so it will carry with it
another round of arctic influenced air as it settles just
upstream. The primary focus associated with this cutoff will be
a clipper system initially. However, there is some indication of
secondary development as the trof begins to transition toward a
negative tilt along the coast. While the ECMWF and many of its
ensembles lead the charge, there remains enough uncertainty that
a blend of ensembles from both the ECENS and GEFS is preferred
as it will take into account both the more progressive and more
amplified solutions. As the trof shifts ENE, will maintain this
blend into the weekend.
Details...
Sun through Mon...
Arctic airmass once again settles just to the W of New England,
but not without its impacts. H92 temps dip as low -13C by early
Mon morning. This suggest cool highs each day, mainly in the
20s, although with high pres cresting wind chills should be
limited. Overnight lows, however are primed for radiational
cooling, but will be mitigated by the now lack of a snowpack.
Still will likely see mins fall as low as the single digits in
sheltered valleys to the teens elsewhere. Strong subsidence is
implied in soundings, which suggests mainly dry conditions. H85
temps are warmer under this inversion than temps below. With NNW
flow gradually shifting toward the NNE, the delta-T values from
SST to H85 hovers around 15C, while to H9, it is closer to 20C.
Therefore, although shallow will likely see light (given only
moisture is at the top of the mixed layer) snow showers across
mainly the outer portions of Cape Cod and possibly Plymouth
county Sun night into Mon as the winds take on a slight E
component. Accums should will remain light.
Tue into Thu...
As cutoff sets up near the great lakes and its attendant
longwave trof continues to dig, the final depth and tilt will
ultimately determine the possibility of secondary coastal
development near the mid Atlantic, after a weakening clipper
impacts the region. At this time, ensemble low locations for the
potential coastal low range from non-existent, to an inside
runner to close to Bermuda, with some clustering near the 40/70
benchmark. However, this much spread is likely to continue into
Sun, until the PV anomaly currently wrapped up the arctic
becomes better sampled. The clipper does ingest some moisture on
Tue as it approaches the Atlantic. This does yield decent
moisture in the DGZ, however overall lift is weak, so SLRs are
unlikely to be maximized. So a more progressive solution
favored by the GFS, with QPF ranging only between 0.1-0.25
inches could stay below advisory criteria. Meanwhile, the more
robust solution would quickly follow the clipper with influence
of coastal low pres Wed-Thu with better lift in the DGZ and
overall more latent-heat energy. There is some precedent for
this solution given some of the ensembles and overall
amplification of the pattern, and should it verify, it has
closer to 0.5-1.00 inches of QPF which may warrant winter
storms. Too early to call on totals at this time, especially
since the more amplified solution also introduces warmer air
(H92 temps average +3C across SE MA). Elsewhere, with H92 temps
generally between
-2C and -6C, mainly SN is expected, along with highs closer to
seasonal normals in the upper 20s to low 30s and lows in the
teens to mid 20s. Something to watch especially late weekend
into Mon.
Fri into the weekend...
Enough breakdown of the upstream Rex to signal a transition. As
opening wave transitions E and moderates, temps look to return
to more seasonable levels, along with mainly dry air.
&&
.AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Tonight/...
Today...high confidence.
Remnant IFR/MVFR conditions will give way to VFR from NW to SE
through 15Z. This will be accompanied by a rapid freeze and
potential for a bit of FZDZ as precip ends. This may make
runways icy. Otherwise, winds will also rapidly shift to the NW
through mid day from NW to SE as well, with the flash freeze
following. Wind gusts 30-35 subside as they shift to the NW and
LLWS should dissipate through 14Z. Overall improvement, timing
may be off a bit in TAF.
Tonight...High confidence.
Mainly VFR with MVFR CIGS gradually developing on Cape.
KBOS Terminal...Moderate to high confidence in TAF.
KBDL Terminal...Moderate to high confidence in TAF.
Outlook /Sunday through Wednesday/...
Sunday: VFR. Breezy.
Sunday Night: VFR.
Martin Luther King Jr Day: Mainly VFR, with local IFR possible
along extreme southeast MA in some light SHSN. Breezy.
Monday Night: Mainly VFR, with local IFR possible along extreme
southeast MA in some light SHSN.
Tuesday: MVFR/IFR conditions possible. Chance SN.
Tuesday Night: Mainly IFR, with local MVFR possible. Chance SN.
Wednesday: Mainly VFR, with areas IFR possible. Breezy. Chance
SN.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Tonight/...
Today...Moderate to high confidence. Potent southerly low level jet
was allowing for SSW wind gusts up to 40 knots on many of our waters
early this morning...especially in heavier rain which was allowing
some of the stronger winds to mix down. Winds should drop below
gale force wind gusts from west to east by mid morning as low level
jet exits the region. However, strong cold front cross the waters
later this morning and early afternoon with NW wind gusts around 25
knots. Gales will need to be converted to small craft headlines.
Tonight...High confidence. NNW wind gusts around 20 knots in the
cold air advection pattern...but seas will remain above small craft
thresholds even though swell will be on the downward trend.
Outlook /Sunday through Wednesday/...
Sunday: Winds less than 25 kt. Areas of rough seas. Local
visibility 1 to 3 nm.
Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of snow showers. Local visibility 1 to 3 nm.
Martin Luther King Jr Day: Winds less than 25 kt. Seas up to
5 ft. Slight chance of snow showers. Areas of visibility 1 to
3 nm.
Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.
Tuesday: Winds less than 25 kt. Local rough seas. Chance of
snow, chance of rain. Visibility 1 to 3 nm.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of snow. Visibility 1 to 3 nm.
Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of snow. Visibility 1 to 3 nm.
&&
.CLIMATE...
Record high temps set yesterday:
PVD 62 in 2018
BDL 60 in 2018
ORH 59 in 2018
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch until 1 PM EST this afternoon for CTZ002>004.
Winter Weather Advisory until 4 PM EST this afternoon for
CTZ002>004.
MA...Flood Watch until 1 PM EST this afternoon for MAZ002>024-026.
Winter Weather Advisory from 11 AM this morning to 4 PM EST
this afternoon for MAZ005>007-013>019.
Wind Advisory until 9 AM EST this morning for MAZ013-015>024.
Winter Weather Advisory until 4 PM EST this afternoon for
MAZ002-003-008>011.
Winter Weather Advisory until 4 PM EST this afternoon for
MAZ004-012-026.
RI...Flood Watch until 1 PM EST this afternoon for RIZ001>008.
Winter Weather Advisory from 11 AM this morning to 4 PM EST
this afternoon for RIZ002>005.
Wind Advisory until 9 AM EST this morning for RIZ002-004-006-
007.
Winter Weather Advisory until 4 PM EST this afternoon for
RIZ001.
MARINE...Gale Warning until 9 AM EST this morning for ANZ230>236-250-
251-254>256.
Small Craft Advisory until 7 AM EST Sunday for ANZ237.
&&
SYNOPSIS...Frank/Doody
NEAR TERM...Frank/Doody
SHORT TERM...Frank
LONG TERM...Doody
AVIATION...WTB/Frank/Doody
MARINE...Frank/Doody
CLIMATE...