Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service New York New York
1056 PM EDT Wed Mar 21 2018
a major winter storm will impact the area through tonight as a
deepening coastal low moves to south and east of Long Island.
The low further deepens and moves near Nova Scotia on Thursday.
Low pressure remains off shore, in the western Atlantic, Friday
into Sunday as troughs of low pressure move through the area. A
low passes to the south of the region Sunday. Meanwhile high
pressure will be building in from the north Friday through
Monday. The high weakens Tuesday and Wednesday as a frontal
system approaches for Wednesday.
Near term /until 6 am Thursday morning/...
impressive snow band with snowfall rates of up to around 5
inches per hour is currently across Long Island. Another band
extends through some of the CT zones, so will leave winter storm
warnings unchanged at this point. Banding is associated with a
deformation zone and is aligned just west of a trough extending
north from a 700 mb low center located east of the del-Mar-VA
peninsula. Expecting the bands to linger mainly east of the
city for the next few hours as the 700mb low shifts east-northeast.
Thinking most rates within these bands will be in the order of
2-3 inches per hour.
Still have gusty winds in the forecast as well with the
deepening of the low and the increase of the pressure gradient.
Temperatures drop off a degree or two from where they are now.
Short term /6 am Thursday morning through 6 PM Thursday/...
some leftover snow showers will move east of the region Thursday
morning. The surface low storm system will be moving away
towards Nova Scotia, deepening as it does so, still allowing for
a tight pressure gradient. Then, the region will still be under
cyclonic flow aloft. So, an abundance of clouds and lower than
normal temperatures continuing along with breezy conditions.
Highs are forecast to reach the lower 40s due to extra clouds
and snow cover.
Long term /Thursday night through Wednesday/...
Thursday night will be dry as one upper low moves to the east in a
broad upper East Coast trough. Another shortwave rotates into the
eastern trough for Friday with upper and mid level energy, as a weak
surface trough rotates around low pressure across the western
Atlantic. Little moisture will be available, and forcing will be
weak. So will have slight chance probabilities for flurries or
Blocking pattern remains through Sunday as eastern trough remains
and ridge builds into the central United States.
Additional shortwaves will rotate through the longwave trough
Saturday into Sunday with low end, slight chances, probabilities of
additional rain and snow showers. A quick moving shortwave will move
out of the Pacific California coast Saturday and move through the
Central Ridge and into the southeast Sunday. This more potent wave
will generate a surface low that moves off the coast south of the
region Sunday. This combination of shortwaves will keep the chances
The western Atlantic low becomes cutoff Sunday night into Tuesday as
the Central Ridge builds to the east, and surface high pressure
builds in from the north. Wednesday there is a lot of uncertainty
as to how quickly the next frontal system will move into the area.
This will be dependent on how quickly the ridge breaks down
Wednesday. So will have slight chance probabilities once again.
Aviation /02z Thursday through Monday/...
major winter storm continues to impact terminals into
A strong low pressure area off the Delmarva coast this evening
will gradually moving well southeast of Long Island tonight.
Moderate to heavy snow will continue from NYC Metro eastward
through 06 to 08z,with LIFR/vlifr conds.
Snowfall rates of 1 to 2 inches per hour for NYC and CT
terminals, with 2 to 3 inches per hour possible for kisp
through 04z to 06z.
Light snow banding should taper from west to east after 08 to
10z for NYC/New Jersey Metro, but light snow could linger at kisp/kgon
through around 12-14z. Conditions gradually improving to VFR Thu morning.
North/northwest winds around 15kt and gusts 25-30 kt likely through the
much of the taf period.
Additional snowfall accumulations:
kjfk/klga/kewr/kteb/khpn/kbdr: 2-5 inches.
Kisp/kgon: 4-8 inches.
Kswf: 1 inch
Outlook for 00z Thursday through Monday...
Thursday night-Friday...VFR. North winds g20-30kt on Thu.
Saturday night-Sunday...low chance MVFR in rain/snow showers.
through tonight, expecting the highest of winds with the passing
storm system to the southeast of Long Island. Storm force winds
look to be marginal but cannot be totally ruled out, left Storm
Warning for ocean zones east of Fire Island Inlet. Gale Warning
for all other waters through tonight. Winds gradually lower
Thursday, but still remain gusty. A few remaining gales in the
morning mainly over eastern waters and ocean waters with Small Craft Advisory
winds elsewhere. Small Craft Advisory conditions linger on the ocean through the
Small craft conditions will likely remain across the ocean waters
Thursday night as low pressure remains to the east, with a gusty
northwest flow. As high pressure builds in from the north Friday
into the beginning of next week, the pressure gradient will remain
weak through Saturday night. A wave of low pressure passing well to
the south Sunday will increase the gradient and ocean gusts and seas
may reach Small Craft Advisory levels Sunday and Sunday night.
a significant precipitation event will impact the area through tonight
with liquid equivalent amounts from 0.50 to 1.50 inches,
highest from NYC and points east. This will fall mainly as snow,
so no hydrologic impact expected.
widespread minor coastal impacts expected with tonight's high
tide along most of the tri-state shoreline. Locally moderate
coastal flooding for the most vulnerable locales in southern
Nassau, as well as along the North Shore of Li and Twin Forks
due to elevated water levels with wave action.
The high tide cycle during the day Thu is the lower of the 2, and
everything points to no impacts attm. If there are any residual
water issues on the South Shore bays, this could produce pockets of
minor for the higher Thu ngt cycle. All the guidance however
suggests no impacts attm.
NYC National oceanic and atmospheric administration weather radio station kwo-35 (162.55 mhz) is off the
air for an extended period of time.
CT...Winter Storm Warning until 8 am EDT Thursday for ctz006>008-
Coastal flood advisory until 4 am EDT Thursday for ctz009>012.
Winter Storm Warning until 6 am EDT Thursday for ctz005-009.
New York...Winter Storm Warning until 8 am EDT Thursday for nyz079-081.
Coastal flood advisory until 4 am EDT Thursday for nyz071-078-
Winter Storm Warning until 6 am EDT Thursday for nyz069>075-
Coastal flood advisory until 3 am EDT Thursday for nyz074-075.
Winter Weather Advisory until 6 am EDT Thursday for nyz067-068.
Coastal flood advisory until 3 am EDT Thursday for nyz080-178-
New Jersey...Winter Storm Warning until 6 am EDT Thursday for njz002-004-
Coastal flood advisory until 3 am EDT Thursday for njz006-106-
Marine...Gale Warning until noon EDT Thursday for anz330-340-345-355.
Gale Warning until 6 am EDT Thursday for anz335-338.
Storm Warning until 6 am EDT Thursday for anz350-353.