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Area forecast discussion 
National Weather Service New York New York
1231 am EST Sat Jan 31 2015

Synopsis...
low pressure will deepen well off the New England coast through
Saturday...while polar high pressure builds in from the west. A
cold front will move through on Sunday as deepening low pressure
approaches from the Ohio Valley. The low passes south of Long
Island Monday and then far offshore Monday night with high
pressure building in its place. The high moves across Tuesday and
offshore Tuesday night. A cold front moves across midweek with
another low passing well offshore late in the week. By that
time frame...high pressure will be centered west of the region.

&&

Near term /until 6 am this morning/...
winds across the interior have really diminished late this
evening. Although low over the Gulf of Maine will continue to
deepen overnight and cold advection will continue...think it will be
tough to get wind advsy level winds here anymore. So am cancelling
the advsy across interior portions of the lower Hudson Valley and
interior southern CT. Rest of advsy remains in effect although
conds now look marginal. Also cut back on end time of the hazard
on Sat. GFS has been too strong this evening and NAM has been a better
fit...with 00z soundings supporting winds diminishing earlier
which was also the case of the 18z run.

Despite the cancellation of the wind advsy...surface winds will still
remain high enough to keep the wind chill advsy as is. A few zones
may fall just short...but it's still close enough to keep it.

The combination of strong winds and low temperatures into the single
digits inland...and around 10 at the coast...produces wind chills
of 10 to around 15 below zero. Regardless...it will be bitterly
cold and precautions will need to taken if exposed to these
elements for any length of time.

For overnight lows...preference was toward a blend of the colder
met MOS and NAM 2m temperatures.

&&

Short term /6 am this morning through 6 PM Sunday/...
strong northwest flow continues on Sat as low pressure lifts up into the
Canadian Maritimes and polar high pressure builds in from the
west. GFS is already too high with the winds and may be overdoing
it on Sat as well. Therefore...the wind advsy may be up too long
and may scale back on the timing later this evening. Preference was
toward a blend of the colder met MOS and NAM 2 M temperatures with highs
15 to 20.

High pressure slides across the area Sat night and then offshore
sun as deepening low pressure approaches from the Ohio Valley.
Clouds will increase late Sat night into sun with a low chance of
snow developing ahead of the system by late sun after/early evening.

Lows Sat night will be considerably warmer...but still below
normal with lows in the teens. West winds will also continue to
diminish. Highs on sun will be in the low to middle 30s. Stayed
closed to a met/mav MOS blend.

&&

Long term /Sunday night through Friday/...
the main focus of the long term is the storm system Sunday night
through Monday. The chance of precipitation is very high and looks
to be mainly snow. The snow forecast has a total of generally 6-12
inches in this time frame...highest across southern CT and lower
Hudson Valley...lowest across Long Island. However...these specific
snow amounts are uncertain and the confidence level is around 40-45
percent...the higher percentage being across the interior zones.

Because of this aforementioned uncertainty and lower
confidence...held off on the Winter Storm Watch. There are more
features that go into the current lower confidence level. One...a
progressing middle level shortwave that does not close off. It exhibits
a rather potent magnitude but swiftly moves across Monday. The
highest positive vorticity advection will be going into Monday
morning so the snow will probably be the heaviest during this
timeframe.

Two...this event is still beyond the 36-48 hour timeframe that is
typical of a watch. The forecasts going into Monday morning have
exhibited wide variance in the position of the low on the order of
about 100 to 200 miles. This has been conveyed in the NAM...CMC
between the last two runs and the European model (ecmwf) 12z compared to 12z
yesterday. This will make all the difference if for example a
further northward trend is made with the models runs tonight. The
NAM and parallel NAM have already shown a more northward trend that
poses a chance for a wintry mix across some coastal sections. This
has been reflected in the forecast so this is a very complex one.

Three...ingredients for this system have yet to come together from
western Canada and southwest Mexico. These will combine Saturday and
Saturday night. Thinking the better sampling tonight into Saturday
will yield less variance in future model runs.

After this system...Monday night until midweek...we will be in a
quasi-zonal middle level flow. A weak low amplitude shortwave moves
across Tuesday with a larger more amplified shortwave moving
approaching Wednesday night. There will be an associated cold front
at the surface approaching Wednesday night into Thursday. There will
be a chance of snow with this.

For late in the week...a low pressure area moves far offshore...more
offshore with the 12z European model (ecmwf) run today...but did not want to totally
make for a dry forecast. Left in a chance of mainly snow for
Thursday into Friday. However...the models have conveyed more of a
progressive solution and less amplified than before so the low is
not that strong offshore and high pressure could prove to be more
dominant in allowing for a drier forecast.

For high temperatures...below normal overall...mainly in 20s except
for Wednesday and Thursday with low to middle 30s. Lows are forecast to
be teens to lower 20s Sunday night and Wednesday night. For other
periods...low temperatures are forecast as follows...single digits
to a little below zero Monday night...single digits to lower teens
Tuesday night...low to middle teens Thursday and Friday night.

&&

Aviation /06z Saturday through Wednesday/...
high pressure slowly builds in from the west through the forecast
period.

VFR. Gusty northwest wind around 310 true...with gusts 30kt to
37kt.

Outlook for 06z Sunday through Wednesday...
late Saturday night-Sunday...VFR.
Sunday night-Monday...potential high impact day. IFR and snow
likely. Chance mixed precipitation. NE-north g 25-35kt possible.
Monday night...becoming VFR as snow comes to an end. North-northwest wind
g20-25kt possible.
Tuesday-Wednesday...VFR.

&&

Marine...
northwest gales will continue on the waters overnight into Sat morning.
The eastern ocean waters could approach storm force gusts. The
combination of strong winds and cold water temperatures from the middle 30s
to lower 40s will also result in at least moderate freezing spray
during this time frame.

Gusty winds will diminish Saturday night into Sunday. Seas will
respond by subsiding through this time frame. Marginal 5 feet seas
may clip the easternmost ocean waters S of Montauk into
Sunday...but sub Small Craft Advisory conditions are likely across the waters
Sunday.

Overall...rough conditions Sunday night through Wednesday. Winds and
seas increase late Sunday night into Monday morning. Ocean seas
increase to 6 to 11 feet through the day Monday...and last into Monday
night. The wind gusts reach 25 knots late Sunday night with gales quite
possible Monday into Monday night. These conditions gradually taper
down early Tuesday. The relatively more quiet period looks to be
late Tuesday morning through early Wednesday morning. There could be
some marginal Small Craft Advisory seas on the outer ocean Tuesday of around 5 feet.
Small Craft Advisory conditions possible once again with the approach of the cold
front towards midweek.

&&

Hydrology...
generally around 0.6 to 1.2 inches of liquid forecast with the
system Sunday night through Monday. Mainly a snow event
forecast...so no hydrologic issues expected.

&&

Okx watches/warnings/advisories...
CT...Wind Advisory until 10 am EST this morning for ctz009>012.
Wind Chill Advisory until noon EST today for ctz005>007-009-
010.
New York...Wind Advisory until 10 am EST this morning for nyz069>075-
078>081-176>179.
Wind Chill Advisory until noon EST today for nyz067>071.
New Jersey...Wind Advisory until 10 am EST this morning for njz002-004-006-
103>108.
Wind Chill Advisory until noon EST today for njz002-004-103-
104.
Marine...freezing spray advisory until 6 PM EST this evening for anz330-
335-338-340-345-350-353-355.
Gale Warning until 6 PM EST this evening for anz330-335-338-
340-345-350-353-355.

&&

$$
Synopsis...jm/dw
near term...dw
short term...dw
long term...jm
aviation...mps/met
marine...jm/dw
hydrology...jm/dw

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