Low pressure along a slow moving cold front off the eastern seaboard brought locally heavy snow to portions of southern Connecticut. A strong upper jet stream enhanced the snow across the Tri-State as the low pressure passed well offshore.
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The episode as NWS OKX wrote it up.
Low pressure along a slow moving cold front off the eastern seaboard brought locally heavy snow to portions of southern Connecticut. A strong upper jet stream enhanced the snow across the Tri-State as the low pressure passed well offshore.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS New York, NY wrote its last area forecast discussion before the first event at Dec 9, 7:24 AM EST, 1 hour 51 minutes earlier.
Area Forecast Discussion
National Weather Service New York NY
724 AM EST Sat Dec 9 2017
.SYNOPSIS...
Low pressure along the Carolina coast tracks south and east of
Long Island today, and off the New England coast tonight. A
series of weak fronts will move through the area Sunday into
Monday. Another area of low pressure impacts the region on
Tuesday and Wednesday. Brief high pressure on Thursday is
followed by another late week low pressure system.
&&
.NEAR TERM /THROUGH TONIGHT/...
Main update is to slow down steady snow development until late
morning into early afternoon. Deformation axis of snow extending
from GA/AL up towards DC area this morning is expected to
expand northeastward during this time ahead of amplifying
longwave trough and approaching southern stream energy. Will
have to evaluate through the day whether the slower onset will
reduce snowfall amounts slightly, although the snowfall taper
is slower than 12hrs ago as well.
Otherwise...water vapor imagery showing strong shortwave energy
diving down the backside of Great Lakes trough early this
morning, helping to amplify the longwave trough and lift
intense southern stream shortwave up the coast today. Quite a
bit of convection developing through Florida and off the SE and
Mid Atlantic US coast in subtropical moisture feed ahead of
these dynamic features, meanwhile while a broad deformation
snow band exists from AL/GA up through the Central appalachians.
Shortwave energy will continue to race up the coast today, with
at least the eastern 1/2 to 2/3rd of CWA under a favorable
right rear of 170-180 kt jet dynamics. At the surface, low
pressure tracks from the Carolina Coast early this morning to
near the 40/70 lat/lon benchmark by this evening.
Snow will increase in coverage/intensity late morning into
early afternoon as large scale lift increases and a bit of the
offshore sub- tropical moisture feed advects towards the coast.
Thermal profiles would support snow across almost all the areas,
outside of some initial mixing with rain at onset for city/LI.
W/W/A's issued yesterday are still in effect, with only slight
changes to snowfall. Models are still indicating some weak mid-
level frontogenesis and negative epv aloft across LI/CT this
afternoon/evening which signals potential for some moderate
snow banding. This presents a low to moderate probability of
1/2 to 1 inch per hour snow fall rates in the afternoon and
evening in vicinity of the warning area. 00z models trended
farther west with qpf axis, which has increased the likelihood
for 3 to 6 inches of snow across much of the advisory area, and
2 to 4 inches of snow into Orange County, where advisory has
been expanded into.
In terms of ptype, thermal profiles are cold enough for most of
the region to be in the form of snow. But an 850-950 hpa warm
layer still appears that it could make inroads into far se
portions of the area late this aft/eve to result in a mixing
with or changeover to rain as low pressure make the closest
approach. The reason for this is that northern/southern stream
phasing of energies does not start taking place until late
today/this evening as the low/mid level low is tracking SE of
LI, which does not allow for enough tightening of the thermal
gradient to ensure cold air all the way to the coast through the
event. Based on an ensemble of thermal profiles, the south fork
of LI has the highest probability a period of mixing with rain
and sleet this afternoon into evening, possibly working
northwest into the north fork of LI and SE New London County in
the evening.
In terms of QPF, models have wavered a bit from run to run and
between each other with QPF but generally still depicting a
range of 1/2 to 3/4 of an inch of liquid equivalent across LI/CT
(highest east), 4 to 6 tenths across NYC/NJ metro and SW CT/SE
NY border, tapering to 1/4 to 4 tenths of an inch for Orange
county. With boundary layer and surface temps holding around
freezing along the coast during the event, and upper 20s to
lower 30s across interior, snow ratios not expected to be too
much above 7-10 inches of snow to 1 inch of liquid.
In terms of snowfall, based on P-type and dynamics mentioned above,
still expecting 5 to 7 inches of snow for SE CT and Eastern LI
(except for far SE portions due to mixing). Farther west a
solid advisory level snow expected, with 3 to 6 inches to around
the NY/NJ metro and the Hudson River. NOTE: Based on the slower
onset of steadier snow, marginal surface temps, and diurnal
solar insolation, expecting roadway snow accumulation to become
more of a concern and hazard starting in the mid to late
afternoon through the evening.
In term of uncertainty, besides the p-type issues for se areas,
the offshore convection could be playing a factor in affecting
magnitude of offshore moisture feed into the region. Based on
variability from run to run between models and current model
spread, snow amount could have to be increased or decreased by 1
to 2 inches from current forecast in spots. Will have to
monitor mesoscale models, satellite and radar trend today.
Once again, along with the slower snow onset, accumulating snow
appears to be slightly slower to taper off than what appeared
12 hrs ago; not until the longwave trough axis begins moving
into the region tonight. Accumulating snow expected to taper
off across the NYC metro by around midnight, and late night
across Eastern LI/SE CT.
&&
.SHORT TERM /SUNDAY/...
Trough axis slides NE Sunday with intensifying low pressure tracking
into the Canadian Maritimes. Cyclonic flow should maintain sct to
bkn cloud cover and perhaps a few flurries as a second weak
shortwave moves through. Blustery day on Sunday with temps likely
struggling to get above 40 degrees for city/coast and above mid 30s
interior with new snow pack and caa flow.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
In general, the extended forecast will be dominated by below normal
temperatures and a progressive pattern with a series of low pressure
systems moving through the area.
Sunday night into Monday will be dry as low pressure quickly departs
to the Canadian Maritimes, and high pressure builds in its wake.
With strong cold advection, lows Sunday night will only reach into
the 20s to near 30, while highs will generally be in the 30s -
around 5 degrees below climatological normals.
By Tuesday, a strong upper disturbance takes a southward trajectory
around a stagnant low centered around the Hudson Bay, with the
attendant surface low moving through the Northeast. There is still
uncertainty with regard to precipitation type and accumulations, but
will continue to monitor. Coastal locations may see a period in the
afternoon-evening where snow transitions to rain, while other
locations should remain all snow.
As the system departs on Wednesday, snow will taper off from west to
east and winds will rapidly increase in a tightened pressure
gradient and strong cold air advection. Temperatures will be 10-15
degrees below climatological normals into Wednesday night, only
slightly moderating on Thursday as brief high pressure moves into
the area.
By Friday, another disturbance rotates into the Northeast, bringing
another chance for snow across the interior and a snow/rain mix
elsewhere. Although temperatures will have moderated some near the
coast, in general below normal conditions will persist.
&&
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Low pressure tracks off the Carolina coast this morning, and into
the Canadian Maritimes tonight.
Onset of snowfall has been delayed a bit from previous
forecasts, and will likely develop more in the 14-17Z time frame
from southeast to northwest. Please see TAFs for exact timing.
Snow becomes heavier thereafter, with the most intense snowfall
likely during the middle of the day into the early evening. Snow
tapers off after 00Z from west to east.
North-northeast flow generally below 12 kt is expected during
the afternoon and evening. Winds veer to the northwest tonight
as the low pulls away.
Terminal Snowfall Forecast:
KJFK: Snowfall rates could reach 1 inch per hour. Around 4-6 inches
of total snow forecast.
KLGA: Snowfall rates could reach 1 inch per hour. Around 4-6 inches
of total snow forecast.
KEWR: Snowfall rates could reach 1 inch per hour at times. Around 4-
6 inches of total snow forecast.
KTEB: Snowfall rates could reach 1 inch per hour at times. Around 4-
6 inches of total snow forecast.
KHPN: Snowfall rates could reach 1 inch per hour at times. Around 4-
6 inches of total snow forecast.
KISP: Snowfall rates could exceed 1 inch per hour at times.
Around 6-8 inches of total snowfall forecast.
.OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY...
.Late Tonight...Snow tapers off from west to east. MVFR or lower
ceilings.
.Sunday...Light snow may linger in the morning near KGON with
possible MVFR/IFR, otherwise becoming mainly VFR. NW-W winds G20-25
kt possible.
.Sunday night-Monday. Mainly VFR, with MVFR possible in isolated
snow showers. WSW-W winds G15-20KT possible.
.Monday night-Wednesday...MVFR or lower is possible with a chance of
snow. A wintry mix or change over to rain is possible Tuesday
afternoon along the south shore of Long Island. SW-W winds G15-25KT
possible Monday night-Tuesday. NW winds G20-30KT possible Tuesday
night and Wednesday.
&&
.MARINE...
Pressure gradient tightens today into tonight. Marginal small
craft gusts are likely to develop on the ocean this afternoon
into tonight, particularly eastern ocean waters. Ocean seas will
begin to build above SCA during this time as low pressure
passes makes closes approach late Saturday into Saturday night.
More widespread SCA gusts expected for all nearshore waters
Sunday in wake of departing low pressure, and likely on the
ocean well into Monday. Winds will briefly diminish Monday
night as high pressure builds across the waters. Another low
pressure system is forecast to impact the area waters Tuesday
and into Wednesday resulting in the potential for SCA conditions
to return. As the low pressure system departs on Wednesday,
gale- force winds may be possible. High pressure only briefly
builds on Thursday, though with the pressure gradient remaining
modest between the departing low and another approaching system,
SCA conditions may persist on the ocean waters through late
week.
&&
.HYDROLOGY...
Generally 1/2 to 3/4 of an inch of liquid is expected across LI/CT(
highest east), 4 to 6 tenths across NYC/NJ metro to SW CT/SE NY
border, decreasing to 1/4 to 4 tenths of an inch for far NW zones
through tonight. The precipitation is expected to fall as mainly
snow, so no hydrologic impacts are anticipated.
No hydrologic impacts are anticipated through the extended
period.
&&
.EQUIPMENT...
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the
air for an extended period of time. See our headline news on
the web at: http:/weather.gov/nyc
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Storm Warning until 6 AM EST Sunday for CTZ007-008-
010>012.
Winter Weather Advisory until 4 AM EST Sunday for CTZ005-006-
009.
NY...Winter Storm Warning until 6 AM EST Sunday for NYZ078>080.
Winter Weather Advisory until 1 AM EST Sunday for NYZ067>069.
Winter Weather Advisory until 4 AM EST Sunday for NYZ070>075-
176>179.
Winter Weather Advisory until 6 AM EST Sunday for NYZ081.
NJ...Winter Weather Advisory until 1 AM EST Sunday for NJZ002-004-
103-105-107.
Winter Weather Advisory until 4 AM EST Sunday for NJZ006-104-
106-108.
MARINE...Small Craft Advisory from 6 AM to 7 PM EST Sunday for ANZ330-
335-338-340-345.
Small Craft Advisory from 1 PM this afternoon to 7 AM EST
Monday for ANZ350-353-355.
&&
SYNOPSIS...MD/NV
NEAR TERM...NV
SHORT TERM...NV
LONG TERM...MD
AVIATION...MD
MARINE...MD/NV
HYDROLOGY...MD/NV
EQUIPMENT...Hazardous Weather Outlook National Weather Service New York NY 325 AM EST Sat Dec 9 2017 NJZ002-004-103-105-107-NYZ067>069-100830- Western Passaic-Eastern Passaic-Western Bergen-Western Essex- Western Union-Orange-Putnam-Rockland- 325 AM EST Sat Dec 9 2017 ...WINTER WEATHER ADVISORY IN EFFECT UNTIL 1 AM EST SUNDAY... This Hazardous Weather Outlook is for northeast New Jersey and southeast New York. .DAY ONE...Today and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Winter Weather Advisory. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. && This Hazardous Weather Outlook provides a summary of potential widespread hazardous weather events that may reach NWS warning criteria. Most long fused NWS watches...warnings and advisories in effect are highlighted. Please refer to the latest NWS forecasts for weather not meeting NWS warning criteria. CTZ005-006-009-NJZ006-104-106-108-NYZ070>075-176>179-100830- Northern Fairfield-Northern New Haven-Southern Fairfield-Hudson- Eastern Bergen-Eastern Essex-Eastern Union-Northern Westchester- Southern Westchester-New York (Manhattan)-Bronx- Richmond (Staten Island)-Kings (Brooklyn)-Northern Queens- Northern Nassau-Southern Queens-Southern Nassau- 325 AM EST Sat Dec 9 2017 ...WINTER WEATHER ADVISORY IN EFFECT UNTIL 4 AM EST SUNDAY... This Hazardous Weather Outlook is for southern Connecticut, northeast New Jersey and southeast New York. .DAY ONE...Today and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Winter Weather Advisory. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. && This Hazardous Weather Outlook provides a summary of potential widespread hazardous weather events that may reach NWS warning criteria. Most long fused NWS watches...warnings and advisories in effect are highlighted. Please refer to the latest NWS forecasts for weather not meeting NWS warning criteria. CTZ007-008-010>012-NYZ078>080-100830- Northern Middlesex-Northern New London-Southern New Haven- Southern Middlesex-Southern New London-Northwestern Suffolk- Northeastern Suffolk-Southwestern Suffolk- 325 AM EST Sat Dec 9 2017 ...WINTER STORM WARNING IN EFFECT UNTIL 6 AM EST SUNDAY... This Hazardous Weather Outlook is for southern Connecticut and southeast New York. .DAY ONE...Today and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Winter Storm Warning. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. && This Hazardous Weather Outlook provides a summary of potential widespread hazardous weather events that may reach NWS warning criteria. Most long fused NWS watches...warnings and advisories in effect are highlighted. Please refer to the latest NWS forecasts for weather not meeting NWS warning criteria. NYZ081-100830- Southeastern Suffolk- 325 AM EST Sat Dec 9 2017 ...WINTER WEATHER ADVISORY IN EFFECT UNTIL 6 AM EST SUNDAY... This Hazardous Weather Outlook is for southeast New York. .DAY ONE...Today and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Winter Weather Advisory. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. && This Hazardous Weather Outlook provides a summary of potential widespread hazardous weather events that may reach NWS warning criteria. Most long fused NWS watches...warnings and advisories in effect are highlighted. Please refer to the latest NWS forecasts for weather not meeting NWS warning criteria. ANZ330-335-338-340-345-350-353-355-100830- Long Island Sound East of New Haven CT/Port Jefferson NY- Long Island Sound West of New Haven CT/Port Jefferson NY- New York Harbor-Peconic and Gardiners Bays- South Shore Bays from Jones Inlet through Shinnecock Bay- Moriches Inlet NY to Montauk Point NY out 20 nm- Fire Island Inlet NY to Moriches Inlet NY out 20 nm- Sandy Hook NJ to Fire Island Inlet NY out 20 nm- 325 AM EST Sat Dec 9 2017 This Hazardous Weather Outlook is for Atlantic coastal waters. .DAY ONE...Today and Tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time that would meet National Weather Service warning criteria. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. && This Hazardous Weather Outlook provides a summary of potential widespread hazardous weather events that may reach NWS warning criteria. Most long fused NWS watches...warnings and advisories in effect are highlighted. Please refer to the latest NWS forecasts for weather not meeting NWS warning criteria.
The national radar mosaic for the moment the first event began.
4 winter weather. Local standard time, as filed.
CT DOT and trained spotters reported 4 to 7 inches of snow. There were also several reports of 6 to 7 inches of snow, but they occurred in period of greater than 12 hours.
CT DOT and trained spotters reported 4 to 6 inches of snow.
CT DOT and trained spotters reported 4 to 6 inches of snow.
Trained spotters and social media reported 4 to 6 inches of snow.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Connecticut in 2017Every state in 2017This day in weather historyWarnings in Connecticut, December 2017
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 731983, 729717, 729720, 729721.