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Displaying AFOS PIL: AFDBOX Received: 2018-01-03 21:28 UTC


959 
FXUS61 KBOX 032128
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
428 PM EST Wed Jan 3 2018

.SYNOPSIS...

A significant winter storm will bring heavy snow, strong to 
damaging winds and coastal flooding Thursday into Thursday 
night. Exact snow amounts and precise location of the rain-snow 
line will be dependent on how close the storm tracks to New 
England. Another blast of arctic air will follow for Friday and 
the weekend. Another storm may affect us early next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...

1 PM Discussion...

Current forecast looks on track. High pressure over our area
keeps conditions dry this afternoon, with sunny/mostly sunny
skies. While temps are expected to be around 10 degrees below 
normal, temps this afternoon are more 'mild' than they've been 
in about a week. With the noontime obs, Nantucket Airport
actually climbed past freezing at 33 degrees! 

Surface winds will remain out of the south/southwest this 
afternoon and evening. High temps generally in the 20s to 
around 30, except low-mid 30s near and along the Cape/Islands.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...

*/ Highlights...

 - Moderate to heavy snow, especially E MA and N RI
 - Blizzard conditions along the E/SE MA and RI coastlines
 - Strong to damaging winds, downed trees, limbs, powerlines
 - Coastal flooding issues for the E MA coastline

*/ Summary...

Explosive, potent winter storm system taking aim on New England
bringing multiple hazards: moderate to heavy snow, low visibility,
strong to damaging winds, coastal flooding, and hazardous seas.

Travel and economic impacts Thursday into Friday with accumulating
snow and white-out conditions. Expect downed trees, tree branches,
powerlines and thus power outages, scattered to widespread with winds.
Flooding of coastal infrastructure, wave action and beach erosion
with astronomically high tides and expected 2 to 3 foot surge more
so with onshore flow. Damage to docks and marinas especially with
the presence of ice.

*/ Overview...

Multiple pieces of energy presently phasing and exploding across FL
beneath a negatively tilting H5 trof axis. Strengthening cyclonic
motions with stratospheric-tropospheric coupling, rapid cyclogenesis
in response to the thermal wind imbalance, H3 jet couplet (RRQ/LFQ)
amplifying in response, a massive bombing surface low taking shape
up the E coast, lowering down to around 950 mb offshore of New England
as it quickly races NNE into SE Canada Thursday morning exiting
Thursday night.

Robust warm-moist integrated water vapor transport cyclonically trowaling
further back along the 295-305K surfaces with beneath the H2-3 jet
coupling and strong divergence / QG-forcing. This as colder air
digs rearward along with the dynamic tropopause noted by potential
vorticity of around 2 PVU and lower potential temperatures. Looking
at strong mid-level SW-NE curving frontogenetical / deformational
banding on the back side of the stacking low column with the clash
of airmasses / low-mid level convergent winds, tightening over time
with storm passage and given the isallobaric / gradient wind response.
Keying especially upon the H85-7 low, coincident potent lift / omega
through the snow growth region, and H85 -5C isotherm. The intense
lift along the banding signatures, monitoring dynamic cooling along
with a neighboring S/E intrusion of a H95-85 warm layer, evaluating
for both the rain / snow / wintry mix line along with the mid-level
lapse rates, looking for any signs of upright convection potential
along with potential instability as thetaE decreases with height.

A lot at play, precipitation dividing lines at work especially around
Cape Cod, banding signatures clearly evident, lift and forcing notably
explosive. Model differences noted between the hydro and non-hydrostatic,
even with the latest 18z guidance wavering. Mass fiends and coincident
dynamics slightly juxtaposed among the guidance, but there is consensus
on how unprecedented this system is, its dynamics, associated lift / 
omega / banding signatures while subtly off from one another roughly
W to E. Incredibly difficult to forecast, quite the headache. Any
tiny shift on the order of 10 miles can make all the difference in
snow amounts, main threats, impacts.

Preference to the blend of the non-hydrostatic / high-res guidance.
Will breakdown the details below providing forecast thinking, high-
lighting areas at greatest risk with respect to specific hazard types.
Guidance continuing to wobble, perhaps due to latent heat / convective
feedback issues. 

Final note, feel snow amounts are overshadowing the bigger impacts
to this system. Incredible to say the least, when is the last time
we saw such a bombing storm, the likes of which CIPS Analogs poorly
score. Strong to damaging winds along with coastal flood impacts
are more than likely to be the bigger players, yielding damage to
infrastructure along with scattered to widespread power outages as
colder air surges in from the W as we go into the late week period.

*/ Moderate to Heavy Snow...

Moderate to heavy snow banding expected, yet uncertain as to exactly
where given subtle spread of mass fields associated with the H85-7
low / H85 -5C isotherm within hydro and non-hydrostatic models. This
lends to low forecast confidence. Just a shift on the order of 10
to 50 miles can make a considerable difference of outcomes as there
is an expectation of multiple snow bands and likely shadow areas
in between. Potential red flags of drier air working in within the
dendritic growth zone as well as H95-85 warm nose intruding, however
it's unclear on the motions and clash of the CCB and WCB over S New
England as the low deepens as it spins by. 

Certain on the immense lift within the atmosphere, contributions to
dynamic cooling, 2-3"/hr snowfall rates, perhaps higher in spots,
and quarter mile visibilities / white-out conditions, suggested by
SREF probabilities. But exactly where, a challenge to determine.
From a consensus of forecast guidance with a nod to probabilistics,
HREF, and CIPS analogs, keying in on E/SE MA and RI with the highest
snowfall amounts of around 12 to 14 inches over E interior MA and
N RI, a general 8 to 12 inches elsewhere with 6 to 9 out into the
CT River Valley. Impacts beginning towards Thursday morning into
evening. 

A coastal front along the SE coast, expected to see a wintry mix,
some parts all rain, that complicates the forecast for the SE coast,
Cape and Islands. Believe it'll immediately go to a heavy snow with
instant accumulation as the storm begins to lift out, winds becoming
W racing colder air E. When all is said and done, the Upper Cape is
forecast to see warning level snows with more advisory level snows
out towards the Outer Cape and perhaps across Marthas Vineyard.

As to snow to liquid ratios, higher N/W, light and fluffy, greater
chance of blowing and drifting, especially as the winds turn westerly
with cold air advection proceeding. S/E lower, heavy and pasty. Keeping
in mind the coastal front, propensity of momentum transfer to the
surface greater on the S/E side, snow will exacerbate downing of tree,
tree limbs, and powerlines. As colder air surges in from the W, the
storm lifting out, any lingering snow likely to be light and fluffy
with 15:1 to 20:1 snow to liquid ratios.

BLIZZARD WARNINGS extended along the coastline where there is a
greater likelihood of verification with heavy snow forecast in
proximity to the coastal front along which winds should exceed
blizzard warning criteria. White out conditions. Downgraded over
the Cape and Marthas Vineyard given the intrusion of warmer air,
snow moving in late as winds turn out of the W and colder air surges
E, expecting a brief period of white out conditions and quickly
accumulating snows on the order of 1 to 2 hours, but not meeting
the 3 hour blizzard criteria. These can change, especially so 
if forecast guidance were to shift the positioning of CCB / WCB 
motions. As we've seen, latest forecast runs have wobbled W to E.

WINTER STORM WARNINGS over the reminder of S New England including
W MA. While winds may be strong over E-interior MA and interior
RI near the coastal front, thinking that our wind gusts are perhaps
too broad and that blizzard criteria will be hard to meet. Can't
rule out white out conditions for a prolonged period of time but
not confident with respect to winds meeting criteria. Will allow
layer shifts to look at it more closely. Perhaps with expected 
blowing snow as winds increase out of the W, the storm lifting 
away, there's the possibility of blizzard criteria. Again, these
headlines may change. 
 
*/ Strong to Damaging Winds...

Strong gradient / isallobaric response to the winds. Unprecedented
low pressure center falling rapidly down to 950 mb over the Gulf
of ME. Pressure falls as high as 6-7 mb/hr. 

Winds picking up Thursday morning out of the NE. Again, a nod to
the coastal front, mixing down of winds will be difficult initially
with the shallow cold layer on the N/W side of the front, easier
S/E. Strongest winds initially confined to SE coastal MA. Looking
at wind gusts as high as 70 mph. 

Challenge is the exact location of the coastal front, with any wobble
will adjust the ability for faster momentum aloft to mix down to the
surface. Feel that perhaps our wind gusts are too broad along the
coastal front, that there will be cutoff to the immediate E of the
coastal front. Given how difficult it is to verify blizzard warnings,
held them to the S/E coastline where the coastal front is expected
to be in close proximity. 

As colder air pushes in from the W, lapse rates steepening, the storm
peeling off, that will be the time in where widespread strong to
damaging over all of S New England is more likely to occur Thursday
afternoon into the overnight period as strong northerly winds turn
out of the W going afternoon into evening. 

*/ Coastal Flooding...

Please see the coastal flooding section below.

*/ Hazardous Seas...

Please see the marine section below. 

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...

Highlights...

* Dangerously cold wind chills Friday into Saturday night
* Another storm may bring rain/snow/mixed precip Mon into Tue with 
  moderating temps
* Turning much colder next Wed

Friday through Sunday...

Brutal cold airmass by SNE standards moves into the region as deep 
vortex settles over New Eng. Core of coldest air Fri night into Sat 
night, moving out Sun with slowly moderating temps. 925 mb temps 
bottom out around -25C which is extreme for SNE. The bitter cold 
will be accompanied by very strong winds Fri into Sat with gradual 
diminishing trend Sat night into Sun. Soundings support gusts to 40-
50 mph Fri into Fri night with gusts still up to 30-40 mph Sat. In 
addition to wind chill headlines, wind advisories may be needed. 
Mainly dry weather expected with exception of a few ocean effect 
flurries on the outer Cape.

Highlights of the cold

* Fri...Wind chills -5 to -20 across much of the region
* Fri night...Lows zero to 10 below with wind chills -20 to -35
* Sat...Highs zero to 10 above with wind chills recovering -5 to -20
* Sat night...Lows zero to 15 below with wind chills -15 to -30

Monday-Tuesday...

Next piece of shortwave energy approaches from the SW with guidance 
indicating another storm lifting north across the region. Thermal 
profiles are problematic suggesting more ptype issues with rain more 
likely in the coastal plain. 

Wednesday...Another arctic blast expected although not as bad as 
this weekend. 

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...

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

Short Term /through Thursday Night/...

18Z Update...
This afternoon through 03z Thu...High confidence remains in VFR
conditions for this timeframe. 

Light southerly winds will become variable this evening, then 
become north towards/after midnight as the coastal storm begins 
to approach from the south.

03z Thursday through Thursday night...High confidence in 
trends. Moderate confidence on exact timing. 

VFR conditions will fall to IFR from southeast to northwest by 
Thursday morning. IFR/LIFR in snow is likely along most terminals
between 12-21z, except a wintry mix or rain across Cape/Islands.
North winds will strengthen Thu morning with strongest gusts along
eastern MA and RI (gusts 30-45 kts) and gusts 50-60 kt Cape Cod,
Islands and Cape Ann. During Thu morning into Thu afternoon, potential
for a period of LLWS with N winds 45-65 kts at 2kft. Blowing and
drifting snow will impact area runways into Thursday night and may
produce locally reduced vsbys, otherwise conditions improve to VFR.

KBOS Terminal...High confidence in TAF. Impacts to the morning
push are likely. 

KBDL Terminal...High confidence in TAF. Impacts to the morning
push are likely. 

Outlook /Friday through Monday/...High confidence.

Friday through Friday Night: VFR. Strong winds with gusts to
45 kt. 

Saturday: VFR. Windy with gusts to 35 kt. 

Saturday Night: VFR. Windy with gusts to 30 kt. 

Sunday: VFR. Breezy. 

Sunday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance SHSN.

Monday: Mainly VFR, with areas IFR possible. Breezy. Chance SN,
chance RA.

&&

.MARINE...

Forecaster Confidence Levels...

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

Short Term /through Thursday Night/...

Dangerously high seas and storm force wind gusts possible 
Thursday into Thursday night. 

Low pressure is expected to undergo rapid intensification as it
passes east of the Benchmark Thursday into Thursday night. The
result will be the potential for northeast wind gusts shifting to
the northwest over this time and potentially gusting between 50
and 60 knots. This will allow seas across the eastern waters to
build to 20-25 feet or perhaps higher depending on the exact 
track of this storm.

Heavy freezing spray is expected with pockets of extreme freezing
spray possible in some near shore waters right behind this
system late Thursday night into early Friday morning. 

This is a dangerous and potentially life threatening situation for
mariners. Please keep up with the latest weather forecasts and
mariners may need to consider returning to port Today.

Outlook /Friday through Monday/...

Friday through Friday Night: gale force winds with gusts up to
40 kt. Rough seas up to 15 ft. Freezing spray, slight chance of
snow showers. Areas of visibility 1 to 3 nm.

Saturday: Strong winds with gusts up to 35 kt. Rough seas up to
13 ft. Freezing spray, slight chance of snow showers. Areas of
visibility 1 to 3 nm.

Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas. Freezing spray,
slight chance of snow showers. Areas of visibility 1 to 3 nm.

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

Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Local visibility 1 to
3 nm.

Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Local rough seas. Chance of rain, slight chance of
snow. Local visibility 1 to 3 nm.

&&

.TIDES/COASTAL FLOODING...

845 AM update...

We have updated the Coastal Flood Watch to a Coastal Flood
Warning. We are anticipating generally moderate impacts north of
Boston and moderate to major impacts along east and north facing
shorelines south of Boston. Although the duration of this event
is short for such a high impact, there are some compensating
factors. We are starting at a very high astronomical tide, 12.1
feet MLLW in Boston and 4.2 feet MLLW in Nantucket, and this 
storm will intensify extremely rapidly with very strong 
northeast winds gusting to 60 mph or higher along much of the 
coastline by the time of high tide. The overnight model runs 
have edged the storm center a little further west as well. Taken
together, we are now anticipating a storm surge of 2 to 2.5 
feet north of Boston and 2.5 to 3 feet south of Boston along 
east and north facing shorelines. Waves will be building rapidly
during the day and will probably have built to around 15 feet 
by the time of the high tide off Cape Ann and across 
Massachusetts Bay and to 20 feet just east of Cape Cod and 
Nantucket. An additional concern is that chunks of sea ice may 
be washed onshore and exacerbate damage in some spots along the 
coast.

We think the coastal flooding along vulnerable shore roads and
in vulnerable basements will be widespread and could have
pockets of inundation up to 6 feet in low lying areas. Waves on
top of the very high water levels will likely damage vulnerable
structures such as decks, docks, beach access stairs, parking
lots, etc. along the shoreline. Some homes and businesses,
especially along the Plymouth County coast, may be damaged by
the combination of high water and wave action. Still another
potential issue is that the cold temperatures will result in
freezing spray on some structures along the exposed shoreline
from Salisbury to Plymouth. More widespread damage of homes and
businesses is possible if waves should build several feet higher
than currently forecast.

The water will probably be very slow to recede in some spots, 
especially with some drains clogged with snow and ice. The 
standing water will freeze and may be in place for an extended 
time.

There may be some minor impacts lingering along Cape Cod Bay 
and Nantucket for the Thursday night high tide.

&&

.CLIMATE...

The past six days were cold, but not cold enough for a record. 
Frigid temperatures relax today. There is the potential for 
record cold again this weekend.

Average temp for 12/28/2017 to 1/02/2018
BOS   9.2   record  1.6 from 12/29/1917 to 1/03/1918
BDL   6.2   record -2.2 from 12/29/1917 to 1/03/1918
PVD  10.8   record  1.9 from 12/29/1917 to 1/03/1918
ORH   4.3   record  0.2 from 12/29/1917 to 1/03/1918 

Record Minimum High (Low Max) Temperatures for Friday 1/5:

BOS  14/1884     
BDL  18/1976
PVD  20/1976    
ORH  14/1904, 1896 
MQE  10/1904 

Record Minimum High (Low Max) and Record Maximum Lows (Low Min)
for Saturday 1/6:

      Max           Min

BOS   7/1896      -10/1896 
BDL   9/1912       -6/1976 
PVD  11/1912        1/1996 
ORH   6/1896      -12/1896
MQE   3/1896      -14/1896

Record Minimum High (Low Max) and Record Maximum Lows (Low Min)
for Sunday 1/7:

      Max           Min

BOS   12/1912     -2/1896 
BDL   13/1996      1/1912 
PVD   12/1912     -1/1912 
ORH   11/1973     -5/1942
MQE    7/1912     -7/1896

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...Winter Storm Warning from 1 AM Thursday to 1 AM EST Friday for 
     CTZ002>004.
MA...Blizzard Warning from 7 AM to 7 PM EST Thursday for MAZ007-015-
     016-018>021.
     Coastal Flood Warning from 11 AM to 4 PM EST Thursday for 
     MAZ007-015-016-019-022>024.
     Winter Storm Warning from 1 AM Thursday to 1 AM EST Friday for 
     MAZ002>006-008>014-017-026.
     High Wind Warning from 7 AM Thursday to 1 AM EST Friday for 
     MAZ022>024.
     Winter Storm Warning from 10 AM Thursday to 1 AM EST Friday 
     for MAZ022-023.
RI...Blizzard Warning from 7 AM to 7 PM EST Thursday for RIZ007-008.
     Winter Storm Warning from 1 AM Thursday to 1 AM EST Friday for 
     RIZ001>006.
MARINE...Storm Warning from 7 AM to 10 PM EST Thursday for ANZ231>235-
     237-250-251-254>256.
     Storm Warning from noon to 10 PM EST Thursday for ANZ230.
     Storm Warning from noon to 8 PM EST Thursday for ANZ236.

&&

$$

SYNOPSIS...KJC/Sipprell
NEAR TERM...Sipprell/NMB
SHORT TERM...Sipprell
LONG TERM...KJC
AVIATION...KJC/Sipprell/NMB
MARINE...KJC/Sipprell/Thompson
TIDES/COASTAL FLOODING...WFO BOX Staff
CLIMATE...WFO BOX Staff