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Area forecast discussion 
National Weather Service New York New York
634 PM EST Sat Jan 31 2015

Synopsis...
high pressure briefly builds in tonight...before a cold front
approaches and crosses on Sunday. Low pressure approaches from
the Ohio Valley and passes just south of Long Island Monday. The
low tracks well to the east Monday night with high pressure
building in its place. High pressure will largely prevail for the
remainder of the week with the exception of a cold frontal passage
late Wednesday. A developing low over the Gulf Coast states late
in the week looks to take a track well south and east of the area.

&&

Near term /through Sunday/...
adjusted temperatures up a few degrees this evening based on latest observation.

Near zonal flow tonight with weak high pressure building in from the
west this evening...and then a polar front approaching from the
Great Lakes.

Winds and gusts gradually subside through midnight...with increasing
high clouds overnight.

Temperatures will not be quite as cold with lows generally in the
teens...except 20s NYC/New Jersey metropolitan...with neutral temperatures advection and
limited opportunity for radiational cooling. Could see some single
digits in Pine barrens and interior tri-state with decoupling before
clouds move in.

Phasing northern stream and SW US shortwave energy begins to dig
into the central US on Sunday with generally west-southwest upper flow.

A weakening polar front approaches the region on Sunday...but
otherwise increasing and lowering clouds ahead of next approaching
storm system. A few snow flakes may be observed over New Jersey very late in
the day. Temperatures generally in the upper 20s to lower 30s.

&&

Short term /Sunday night through Monday/...
main story will be next in a series of winter storms affecting the
region Sunday night into Monday.

Models are in general agreement with low pressure taking shape
over the central plain tonight...tracking into the Ohio Valley on
Sunday and then just south of the region Sunday night. Overall
trend has been slightly further north and wetter with this system.

Based on coupled jet structure...tight low /mid-level thermal
structure...and Gulf moisture feed of 2-3 Standard precipitable waters ...confidence
is high in at least a 3/4 to 1 1/2 inch quantitative precipitation forecast event for the entire
area. This is borne out in sref/gefs/cmce 1 inch/24 hour quantitative precipitation forecast probs.

Significant uncertainty lies in p-type...particularly along the
coast...with a spread of about 50 miles between operational
solutions and ensemble means in how close to the coast the low
gets and the position of the tight thermal gradient across the
region. Sbu ensemble sensitivity showing this north/S track uncertainty
in the 00z gefs/cmce/ECMWF ensembles...with sensitivity lying in
degree of phasing/interaction between northern stream shortwave
energy dropping down through Montana and the cutoff upper low over
the SW US...and resultant strength of trough approaching the East
Coast Sunday night/Monday and upstream ridging. A stronger
trough...meaning more upstream ridging...and a further north
track. This interaction is not complete for another 24 hours...so
could take until then for confidence in p-type forecast increases.

With confluent flow across northern New England/southeast Canada...Arctic
high should be locked into that area. Prefer tighter thermal
structure aloft of NAM/ECMWF/can versus more diffuse thermal
structure of GFS in this situation...but question is location of
this baroclinic zone. Model solutions pointing to differing
degrees of warming in the 800-950 layer Monday morning into early
after...but trend is towards more warming.

With this said...northwest tier of the tri-state looks to be
mainly snow. Biggest forecast challenge is for coast...especially
NYC/NJ/Li...in amount of sleet/fzra/ra versus snow. 12z GFS/gefs
are further north with low track...just south of Li Monday
afternoon...which would imply more in the way of warming
aloft...and more in way mixing with sleet and freezing rain and
even rain for Li/NYC. 12z Gem has trended in that direction as
well. 12z NAM...would point to mainly snow for CT and lower Hudson
Valley...with a mix of significant snow/sleet accumulate for
NYC/Li/Metro New Jersey. 00z European model (ecmwf)...is similarly colder and a bit farther
south as with the NAM. Have taken a middle of the Road solution
based on the uncertainty...with a slightly wetter and warmer
forecast.

Even with continued northward trend...highest confidence in
significant snow/sleet/ice across interior NE New Jersey...and most of the
lower Hudson Valley and CT. Have upgraded to warning there for 5
to 10 inches of snow/sleet and up to 1/4 inch of ice. Interior
portions of lower Hudson Valley and SW CT...more in the 8 to 14
inch range with less ice/sleet.

Even for NYC/New Jersey metropolitan and Li...could see a quick 3 to 5 inch
snowfall on the front end with southern stream moisture and strong
lift late Sun night/early Monday morning before any mixing. After
changeover...a prolonged period of freezing rain/sleet (1/4 inch of ice)
possible for northern half of Li/NYC and NE New Jersey...with cold air
drainage down the river valleys. Have maintained a watch here with
uncertainty if we changeover to more rain...particularly for south
coastal areas. The one aspect to keep in mind is if coastal areas
do go over to rain...there is potential for urban flooding issues.
See hydrology section for more information.

Any rain/mixed precipitation should gradually change back to snow from northwest
to southeast Monday afternoon/eve. Even some signal of deformation banding
on the backside...with accumulating snow back down to the coast.
With cold air crashing back down to the coast...potential for
flash freeze conditions for Monday evening commute for city/coast
in wake of a washing rain. So to say the least...a complicated
forecast for the NYC/New Jersey metropolitan and Long Island...which could still
see significant impacts even if it is not all frozen.

&&

Long term /Monday night through Saturday/...
a broad upper trough will remain in place through the upcoming week
from the Canadian prairie provinces of western Canada southeast into the
middle Atlantic region. This will keep a steady stream of polar air
masses moving across the region with generally unseasonably cold
conditions. This season has been typified by this flow regime with
no block over Greenland. Occasionally...a strong short wave briefly
amplifies the flow...but remains progressive.

The only chance for precipitation looks to be with a polar cold front Wednesday
into Wednesday night...which will be in the form of scattered snow snow showers.
Models have trended well south and east with a late week coastal low
moving out of the Gulf Coast states. Thus...have trended down to the
point where there is no mention of precipitation late in the week.
Interestingly enough though...models have been wavering back and
forth with these systems...so perhaps not completely out of the
Woods.

The only day of the week that looks to be near normal with respect
to temperatures is Wednesday ahead of the next cold front.

&&

Aviation /00z Sunday through Thursday/...

**high impact event Sunday night through monday**

High pressure over the terminals this evening weakens tonight as a
warm front and associated low pressure approach. The warm front will
be in the vicinity by 00z Monday. Light snow will be developing late
in the afternoon mainly west of the NYC terminals...and become
likely around 00z Monday with conditions lowering to IFR. There is
still some uncertainty as to the timing of the beginning of the
snow.

Gusty northwest wind subside by 03z with the wind becoming more
westerly...generally under 10 knots.

Outlook for 00z Monday through Thursday...
Sunday night-Monday...high impact period. IFR highly likely as snow
develops Sunday evening...then continues through the overnight. A
wintry mix of sleet...snow and freezing rain becomes likely early
Monday morning at the NYC metropolitan terminals and across Long Island.
The wintry mix pushes farther north during Monday morning and
continues into the afternoon before going back to all snow before
ending Monday evening.
Monday night...becoming VFR as snow comes to an end. North-northwest wind 15
to 20 knots with gusts up to 30 knots.
Tuesday...VFR.
Wednesday...VFR. A chance of snow showers Wednesday afternoon and
Wednesday night with locally MVFR to IFR conditions.
Thursday...VFR. Northwest gusts 20 knots.

&&

Marine...
Small Craft Advisory conditions for the rest of the night with a gradually
diminishing northwest flow. 5 to 9 feet seas will gradually subside to
less than 5 feet during the overnight hours.

Tranquil conds on the waters sun as high pressure builds overhead and
departs. Conds ramp up to Small Craft Advisory levels late Sunday
night into Monday morning ahead of approaching low pressure. A few
gale gusts may be possible on the ocean.

There is the potential for a marginal gale event Monday night on the
backside of deepening low pressure lifting up into the Canadian
Maritimes. Winds and seas are then forecast to subside below Small Craft Advisory
levels on Tuesday with high pressure building across the waters.
Marginal Small Craft Advisory conditions are possible on the ocean waters Wednesday in a
pre-frontal SW flow...and then in the northwest Post-frontal flow on Thursday.

&&

Hydrology...
generally 1 to 1 1/2 inches of liquid forecast with the system
Sunday night through Monday. Most of this will be snow and sleet
across NE New Jersey...lower Hudson Valley and CT.

Across Li/NYC there is a potential for a period of heavy
rain...with some models signaling up to 2 inches of quantitative precipitation forecast.
Although this potential is low...if model trends continue
north...this potential would increase...resulting in urban
flooding issues.

No significant widespread precipitation is forecast for the remainder of the
period.

&&

Tides/coastal flooding...
there is a low probability of minor coastal flooding thresholds
being reached with the Monday morning high tide cycle along the
western South Shore bays and western portions of Li sound.

&&

Okx watches/warnings/advisories...
CT...Winter Storm Watch from Sunday evening through Monday
afternoon for ctz011-012.
Winter Storm Warning from 7 PM Sunday to 6 PM EST Monday for
ctz005>010.
New York...Winter Storm Watch from Sunday evening through Monday
afternoon for nyz071>075-078>081-176>179.
Winter Storm Warning from 7 PM Sunday to 6 PM EST Monday for
nyz067>070.
New Jersey...Winter Storm Watch from Sunday evening through Monday
afternoon for njz004-006-104>108.
Winter Storm Warning from 7 PM Sunday to 6 PM EST Monday for
njz002-103.
Marine...Small Craft Advisory until 1 am EST Sunday for anz330-335-338-
340-345.
Small Craft Advisory until 6 am EST Sunday for anz350-353-355.

&&

$$

Synopsis...NV/dw
near term...NV/dw
short term...Nevada
long term...dw
aviation...met
marine...NV/dw
hydrology...NV/dw
tides/coastal flooding...Nevada

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