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fxus61 kokx 201127 

Area forecast discussion
National Weather Service New York New York
727 am EDT Tue Mar 20 2018

Arctic high pressure will begin to retreat to the north as a
significant low pressure system approaches from the south. The
developing coastal system will impact the area through
Wednesday, before finally departing to the northeast into the
Canadian Maritimes on Thursday. High pressure then builds from
eastern Canada through the weekend. Another storm system may be
possible for early next week.


Near term /until 6 PM this evening/...
with the antecedent dry conditions due to the prevailing Arctic
high, the onset of any precipitation expected with the
developing coastal storm has once again been delayed until
afternoon or evening. Any precipitation will initially be light
and largely confined to the southern-most areas - northern NJ,
the NYC Metro and Long Island. With saturation expected to be
slow and precipitation light, any evaporative cooling will be
minimal, so precipitation type may initially be rain or perhaps
a slushy rain/snow mix as high temperatures will be in the upper
30s to lower 40s. Temperatures are still around 10 degrees
below normal for this time of year.


Short term /6 PM this evening through Thursday/...
the main story is the developing Nor'easter. Winter storm
watches have been converted to warnings across all areas except
eastern Suffolk County, where the highest uncertainty in
precipitation type resides. Steadier precipitation is expected
to develop after around midnight from south to north tonight,
becoming more intense through the Wednesday morning commute.
Areas from about NYC eastward will also need to be monitored for
a potential Blizzard Warning with strong winds around 20-30 mph
with gusts up to 45 mph are expected. Primary uncertainty may
be with visibilities, as snow ratios will be lower across these
areas leading to a wetter, heavier snow.

Snow totals have once again been increased. Initially
precipitation types will be mixed as strong easterly flow above
the surface advects warmer temperatures westward. For now went
with a GFS/NAM blend for precipitation types. It should be
noted that the NAM tends to be warmer in these warm advection
scenarios, which would lead to more significant accumulations of
freezing rain for Tuesday night into Wednesday morning, but
based on similar events a mix of sleet, wet heavy snow and
perhaps minimal accumulations of freezing rain seem more likely,
especially closer to the coast.

By Wednesday afternoon to evening, the storm intensifies amidst
strong diffluence/divergence aloft as the upper low passes just
to the south. Given strong convergence at the surface to the
northwest of the low and vorticity maximized in a corridor
roughly from Connecticut through NYC into NJ, expect the
development of a potentially significant snow band, with any
mixed precipitation quickly transitioning to heavy snow as a
result of dynamic cooling. The heaviest snow rates will be
possible around this time, with 1-2"/hr possible. Additionally,
temperatures aloft will rapidly cool as the upper low passes
just offshore, which may provide enough elevated instability for
charge separation, and thundersnow with locally higher rates.
As the system ejects to the east-northeast, the snow band(s)
will rotate eastward, allowing any remaining areas still in
mixed precipitation to transition to all snow as well. For some
areas farther east, particularly eastern Long Island and
southeast Connecticut, the time frame after 8 PM as the band(s)
pull east may be the period of best snowfall potential with the
highest rates of accumulation. Also note, that given this is a
late season event and temperatures will be somewhat marginal,
snowfall is once again expected to be heavy, and combined with
strong winds may lead to downed trees and powerlines.

High pressure then builds into the area again following the
departure of the low pressure system, allowing precipitation to
taper off from west to east during the early morning. At least
light snow may linger across eastern Long Island and Connecticut
through the morning rush, but the more significant accumulations
will have ended. Conditions will remain breezy on Thursday, with
below normal temperatures continuing.


Long term /Thursday night through Monday/...
generally dry conditions will continue through the first half
of the weekend. Some weak forcing may spark off a few snow
showers or flurries late Saturday with an upper level low off
the New England coast, but not enough confidence to put it in
the forecast as of yet. However, the bigger story will be the
potential for another low pressure system to affect the region
for the second half of the weekend.

There are significant differences in the model solutions, both in
the deterministic and ensemble models, for the second half of the
weekend and the potential low pressure system to affect the area.
The main differences Stem from orientation of a strong 1043 mb
surface high pressure over southern Canada Saturday that digs all
the way south into Florida and the southeast US coast. The 19 12z
European model (ecmwf) pinches off a piece of this high Saturday night, giving an
area of low pressure developing over the mid-west a path between the
two highs to move toward our region. The 19 12z GFS does not pinch
off this high as notably as the ECMWF, with more of a cold air
damming signature noted on Sunday, when the European model (ecmwf) pushes the low off
the Carolina coast, with our region on the northern fringes of the
precipitation field. The low is then forecast to pass well south of
our area and then east out to sea Sunday night. The GFS suppress the
low well south and weakens it. This latest model run of the European model (ecmwf) is
more in line with the GFS. Given forecast uncertainty, will not make
much in the way of changes.

Proximity of the low to the coast will determine precipitation
types. If the European model (ecmwf) is to be believed, the track is a bit different
to previous storms, at least with its approach to the area, with a
more west to east track, then head northeast east, as opposed to
development or redevelopment off the mid-Atlantic coast and heading
northeast. However, it will be cold enough for some snow.

Temperatures during the long term will average below normal with a
persistent northwesterly flow.


Aviation /12z Tuesday through Saturday/...
high pressure gives way to a series of lows passing to the south and
east of the area, the first this evening, and then another on

VFR today and through the evening with lowering clouds. Light
NE winds this morning gradually ramp up during the day. Gusts to
around 20 kt are expected at the coastal terminals in the
afternoon and increasing to 25-30 kt into tonight. Inland gusts
will be a bit weaker.

There is a chance of a light wintry mix developing this
evening. MVFR is possible late at night as wintry precipitation
moves north. The brunt of the precipitation is currently
forecast to develop on Wednesday.

New York Metro enhanced aviation weather support...

Detailed information, including hourly taf wind component forecasts,
can be found at: http:/www.Weather.Gov/zny/n90

Kjfk taf comments: timing of gusts may be off an hour or two this

The afternoon kjfk haze potential forecast is yellow...which implies
slant range visibility 4-6sm outside of cloud.

Klga taf comments: timing of gusts may be off an hour or two this

The afternoon klga haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.

Kewr taf comments: timing of gusts may be off an hour or two this

The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.

Kteb taf comments: timing of gusts may be off an hour or two this

Khpn taf comments: timing of gusts may be off an hour or two this

Kisp taf comments: timing of gusts may be off an hour or two this

Outlook for 12z Wednesday through Saturday...
Wednesday...snow and sleet with IFR or lower conditions
likely. NE winds g20-35kt.
Thursday-Friday...VFR. North winds g20-25kt on Thu.
Saturday...MVFR possible late in chance of rain/snow.


as the first of two lows approaches late this afternoon, winds and
seas should quickly ramp up, with gales arriving on the western
ocean waters by late afternoon, and then out east this evening. They
should however take a while to make it to the non-ocean waters, and
while there could be a few gusts up to 35 kt at times tonight, the
main push for gales on those waters should arrive daytime Wed as the
second stronger low intensifies off the mid Atlantic coast and moves
slowly east on Wed. Storm force winds with gusts 50-55 kt expected
daytime Wed on all the ocean waters, the out east into Wed evening.
Seas on Wed may build as high as 17 ft on the ocean and 7 ft on the
central/eastern sound.

Except for morning gales on the outer ocean waters, Small Craft Advisory conds
expected on all waters through the day on Thu, then on the ocean Thu

Small Craft Advisory conds are possible on Sunday mainly on the ocean waters as winds
increase with the approach of another low pressure system.


it will be mainly dry through tonight.

There is the potential for a prolonged period of precipitation from
Tuesday through Wednesday night. Total liquid equivalent precip
should range from 0.75 to 1.50 inches, falling mainly as snow
and sleet, so no hydrologic impact expected.


Tides/coastal flooding...
prolonged NE-north flow will push water levels up Tue night into
Wed night. Departures of about 2-3 ft for moderate flooding,
and 1-1.5 ft are needed for minor flooding for many locations.

It now appears that S Nassau should see moderate impacts with the
Tue daytime high tide as winds will be stronger initially, with
widespread minor impacts mainly along the SW Suffolk South
Shore bays and in the western sound.

With NE gale to storm force winds going into the late Wednesday
morning/early afternoon high tide cycle, widespread minor to
moderate impacts are likely for the Wed late morning/early afternoon
high tide. Latest guidance has trended upward with surge for this
tidal cycle, and have manually increased those values for the North
Shore and bays of eastern Long Island where winds will be strongest
and wave action will cause additional runup.

Another round of minor to locally moderate coastal flooding likely
for the Wed night high tide cycle. There is more guidance spread
with this tidal cycle, due to competing factors of tidal piling and
energetic wave energy build water levels along the coast, versus
north/northwest gales pushing water away from the coast. Will have to continue
to monitor this tidal cycle, as guidance typically has a low bias on
the back end of multiple-cycle surge events.


NYC National oceanic and atmospheric administration weather radio station kwo-35 (162.55 mhz) is off the
air for an extended period of time.


Okx watches/warnings/advisories...
CT...coastal flood advisory from noon to 6 PM EDT Wednesday for
Winter Storm Warning from midnight tonight to 8 am EDT
Thursday for ctz005>012.
Coastal flood advisory from 1 am to 4 am EDT Wednesday for
New York...coastal flood advisory from noon to 6 PM EDT Wednesday for
Winter Storm Watch from late tonight through Thursday morning
for nyz079-081.
Winter Storm Warning from midnight tonight to 8 am EDT
Thursday for nyz067>075-078-080-176>179.
Coastal flood advisory from 10 am to 2 PM EDT Wednesday for
Coastal flood advisory from 1 am to 4 am EDT Wednesday for
Coastal Flood Warning from 9 PM this evening to 2 am EDT
Wednesday for nyz179.
Coastal Flood Warning from 9 am to 3 PM EDT Wednesday for
Coastal flood advisory from 11 PM this evening to 4 am EDT
Wednesday for nyz080.
New Jersey...Winter Storm Warning from midnight tonight to 8 am EDT
Thursday for njz002-004-006-103>108.
Coastal flood advisory from 10 am to 2 PM EDT Wednesday for
Marine...Gale Warning from midnight tonight to 6 am EDT Thursday for
Gale Warning from 6 am to 6 PM EDT Wednesday for anz335-338.
Storm Warning from 6 am to 6 PM EDT Wednesday for anz353-355.
Gale Warning from 3 PM this afternoon to 6 am EDT Wednesday
for anz353-355.
Storm Warning from 6 am Wednesday to midnight EDT Wednesday
night for anz350.
Gale Warning from 6 PM this evening to 6 am EDT Wednesday for


near term...Maryland
short term...Maryland
long term...Goodman

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