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Area forecast discussion 
National Weather Service New York New York
720 am EST Thursday Mar 5 2015

Synopsis...
an Arctic front will slide to the southeast this morning.
Meanwhile...a series of weak waves of low pressure will track along
a stationary front to the south of the region. Canadian high
pressure builds in tonight through Friday...then builds to the
south through early next week as several weak impulses pass to the
north. The high slides offshore Monday night and Tuesday. A cold
front passes through on Wednesday...followed by Canadian high
pressure for Thursday.

&&

Near term /until 6 PM this evening/...
forecast on track this morning...with snow of moderate to heavy
intensity developing across NYC/New Jersey metropolitan and Li...with snowfall
rates of up to 1 inch per hour. Light to moderate snow to the
north. Difficult travel conditions expected through the tail end
of the morning commute and into this afternoon with snow covered
roads and temperatures dropping below freezing and causing icing
of untreated surfaces.

Otherwise...models in good agreement with deep trough axis over
the central US gradually sliding to East Coast by this
evening...and then offshore tonight. Ahead of it moist subtropical
Pacific moisture plume riding into the region is evident in WV
imagery.

At the surface...a series of low pressure waves will track NE
along a stationary front to the south today...tapping into this
moisture...ahead of approaching upper trough axis and under
increasingly favorable entrance region of a 200kt upper jet.

Biggest model differences compared to 12 to 24 hours ago was slower
column cooling early this morning by about 3-4 hours...but a
slightly farther north track of moisture plume through the day
today meaning higher quantitative precipitation forecast. Overall this is lending to a fairly
similar forecast of snow amounts.

Arctic cold frontal passage expected from northwest to southeast between 10z to
15z...with temperatures in the lower to middle 30s...falling into the upper
20s late this morning...and down into the lower to middle 20s this
afternoon. Road conditions expected to deteriorate in its
wake...and coinciding at least part of morning commute. Icy
conditions and snow covered roads expected for after/evening commute as
well.

Potential for snow to be heavy at times this morning into early
afternoon along the coastal plain...with modest frontogenetic
forcing coupled with strong jet dynamics. Sref is indicating
likely probability of 1" per hour snowfall rates during this time for
NYC/New Jersey metropolitan and Li. Sbu WRF showing potential for 1/2 inch quantitative precipitation forecast
between 7 am and 1 PM across southern portions of Li/NYC. Snow
should gradually taper off in intensity and coverage from northwest to southeast
this afternoon as shortwave trough approaches and offshore
stationary front slides well offshore.

Region is on edge of a tight precipitation gradient. Have relied on a
oper/high res ensemble approach to quantitative precipitation forecast...with generally a 1/10th
or less quantitative precipitation forecast Orange County to close to 7/10 inch of quantitative precipitation forecast across
southeastern Li. The highest probability for 1/2 inch liquid quantitative precipitation forecast remains
along southern portions of the NYC/New Jersey metropolitan and Li. Snow to liquid
ratios will increase through the morning into afternoon...with
heavy wet snow early this morning become light and powdery by this
afternoon.

In terms of snowfall totals...a general 4 to 7 inches of snow
still expected for NYC/New Jersey metropolitan and Li...with highest amounts
across southern portions. Warning continues here. Potential for 2
to 5 inches for coastal CT and southeastern CT...the rest of NE
New Jersey...and southern portions of lower Hudson Valley. Highest amounts
across southern sections. Advisory continues for this area...and
have expanded advisory into northern Middlesex and northern New
London based on trajectory of moisture plume and reports of up to
1/2 inch there already. Finally...with a sharp gradient in precipitation
across areas far n&w of NYC...between dusting to 3 inches expected
from northwest to southeast...but not enough confidence for an advisory at this
time.

Any lingering snow across southeastern Li comes to and end this
evening...with frigid and but drying conditions tonight. Temperatures
expected to drop into the single digits...lower teens NYC metropolitan...on
gusty northwest winds. Windchills likely dropping to around zero for much
of the region by Friday morning.

&&

Short term /6 PM this evening through 6 PM Friday/...
high pressure builds in from the west Thursday night. Skies will
clear from west to east. Winds should diminish late and with dry
conditions...expecting an unseasonably cold night with
temperatures falling into the single digits for most locations and
lower to middle teens in the NYC metropolitan.

&&

Long term /Friday night through Wednesday/...
a mean trough will remain east of The Rockies through early next
week. A split flow then develops across the Continental U.S. With a fast active
northern stream across southern Canada and a broad trough in the
southern stream extending from the central US through Mexico. Zonal
500 mb flow develops across the northeast as a result.

Overall...expect mostly dry conditions with highs warming into the
40s by the middle of next week. A decent shortwave moves through the
northeast Friday night...but strong subsidence with limited moisture is
expected to keep the local area dry. A trough of low pressure
approaches the area Sat and moves through Sat night. Downsloping
flow aloft will likely keep precipitation confined to the windward side of
the Appalachians with only perhaps flurries or a few snow showers at
best late Sat night. The NAM/GFS are indicating a weak low pressure
system moving from the Great Lakes through the New England on
Sunday. Ec is much weaker with no precipitation. Have maintained dry forecast
as precipitation remains confined mainly to the north where better dynamics are
present.

Final northern stream shortwave passes through Monday. GFS is slightly
more amplified aloft with the vorticity maximum passing directly over the
area...although not much precipitation due to ridging nosing in from the S.
Ec is further north. Have maintained schc probability of precipitation.

SW-west flow aloft then develops at 500 mb...although large differences
become prevalent by the middle of the week. The GFS becomes much
more amplified Wednesday/Thursday with southern stream energy becoming picked
up in the flow and passing near the area Wednesday. Ec is much flatter
with dry weather prevailing. Remaining dry weather then prevails
possibly until middle week.

Temperatures will start off below normal with lows in the teens Friday night
and lower 30s Sat...but a moderation will then commence early next
week as heights aloft gradually rise...with temperatures near normal in the
middle to upper 40s for highs and lower 30s for lows next week.

&&

Aviation /12z Thursday through Monday/...
waves of low pressure ride along the cold front southeast of Long
Island. Periods of snow through the day...moderate to heavy near
the coast through the early afternoon. IFR and below through the
day for most terminals except for kswf which will be north of much
of the snow...so MVFR to IFR there.

Snow tapers off late this afternoon into early evening when
conditions are expected to significantly improve.

Winds will be out of the northwest around 10-12 knots through tonight
with some gusts to 15-20 knots today. Winds diminish late tonight
into Friday.

Overall...higher confidence with winds and lower confidence with
categorical changes which could vary a few hours with subsequent
forecasts.

Expected runway snow accumulations:
kisp...6-8 inches.
Kjfk/klga/kewr/kteb/kgon...4-6 inches.
Khpn/kbdr...3-5 inches.
Kswf...1-2 inches.

... Metropolitan enhanced aviation weather support...

Detailed information...including hourly taf wind component forecasts
can be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)

Kjfk fcster comments: forecast timing of category changes could
differ 1-3 hours from observed.

Klga fcster comments: forecast timing of category changes could
differ 1-3 hours from observed.

Kewr fcster comments: forecast timing of category changes could
differ 1-3 hours from observed.

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

Kteb fcster comments: forecast timing of category changes could
differ 1-3 hours from observed.

Khpn fcster comments: forecast timing of category changes could
differ 1-3 hours from observed.

Kisp fcster comments: forecast timing of category changes could
differ 1-3 hours from observed.

Outlook for 12z Friday through Monday...
Fri-Mon...mainly VFR.

&&

Marine...
Small Craft Advisory conditions continue on the coastal ocean waters
into Friday morning as a series of low pressure waves tracks to the
south of the waters and high pressure builds in from the west.
Marginal Small Craft Advisory gusts today...with strongest winds tonight. Seas will
run 4 to 6 feet through the period...with southerly swells predominant
today.

Light freezing spray expected to develop this afternoon across the
ocean waters...possibly becoming moderate late tonight. A period of
freezing spray possible on Li sound as well late tonight.

Sub Small Craft Advisory conds return Friday as high pressure builds over the waters.

Small Craft Advisory conds are possible...mainly on the ocean waters Sat in the wake
of a trough of low pressure. Otherwise...sub-advsy conds are expected
through the period.

&&

Hydrology...
1/10 to 7/10 inch liquid equivalent precipitation today. This
will be frozen...so hydrologic impacts are not expected.

No significant precipitation is expected through early next week.
However...temperatures forecast to warm into the 40s may result in the
start of ice break up on area rivers and streams.

&&

Okx watches/warnings/advisories...
CT...Winter Weather Advisory until 7 PM EST this evening for
ctz007>012.
New York...Winter Storm Warning until 7 PM EST this evening for
nyz072>075-078>081-176>179.
Winter Weather Advisory until 7 PM EST this evening for
nyz069>071.
New Jersey...Winter Storm Warning until 7 PM EST this evening for njz006-
106>108.
Winter Weather Advisory until 7 PM EST this evening for njz002-
004-103>105.
Marine...Small Craft Advisory until 11 am EST Friday for anz350-353-355.

&&

$$
Synopsis...24/NV
near term...Nevada
short term...Nevada
long term...24
aviation...jm
marine...24/NV
hydrology...24/NV

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