Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
350 PM EST Sat Dec 27 2014
high pressure will slide off the middle Atlantic coast through
tonight as a cold front approaches from the west. The front will
move across on Sunday...and then stall off the southern middle
Atlantic. A wave of low pressure riding along this front may
affect the region late Monday night through Tuesday evening.
Otherwise...high pressure will dominate through Friday...with
another frontal system approaching for the start of next weekend.
Near term /until 6 am Sunday morning/...
expect increasing clouds tonight ahead of the approaching cold
front...and likely pop well north/west of NYC...and at least
chance of showers late tonight except Long Island. Lows tonight
should range from the middle 40s in Midtown NYC...to the middle/upper
30s across eastern Long Island and well inland.
Short term /6 am Sunday morning through Monday night/...
cold front should be accompanied/followed by some light rain as it
moves through in the daytime Sunday. Shot of positive Theta-E
advection ahead of the lagging 800 mb cold front...and lift via
passing middle level shortwaves and upper divergence with an
anticyclonic jet streak to the north should result in a period of rain
for most places...especially NYC metropolitan and Long Island Sunday
afternoon as these ingredients come together. GFS/NAM MOS blend
accepted for highs...generally within a couple degree either side of
Any lingering light rain mainly for NYC metropolitan and Long Island
early Sunday evening should end by late evening as the 800 mb cold
front passes to the southeast...but skies may not clear very much...even
north/west as another middle level shortwave and the right rear
quadrant of the upper jet swing across. Cold air advection on northwest-north flow
especially late at night should lower temperatures to the 30s...possibly
just below freezing in the interior valleys.
Long term /Tuesday through Saturday/...
a return to nearly zonal flow early through midweek. Periodic
shortwaves move across within the quasi zonal flow to give
reinforcement of colder air. Relatively strongest one with support
of upper level jet streaks increasing is on Tuesday.
Cutoff low in the southwest U.S. Moves east slowly midweek into late
week. This pushes heights up to the east of it. This gives more of a
ridging pattern Friday into next weekend.
Believe the European model (ecmwf) more than the GFS with the progression of the
upper level low...taking a much slower track for this.
For Monday at the surface...a very large magnitude...1050mb at
least...high pressure area builds into the northwest U.S. This will
be a source for much colder air. The high gradually moves southeast
into the south central U.S. Through midweek with the local area
air mass becoming colder. Will have to monitor potential for surface
low development along a front well south of the region for late
Monday night through Tuesday evening. Only sref and NAM are
portraying this wetter solution for this time frame while
GFS...parallel GFS...ECMWF...and CMC are dry and have any precipitation
well south of the region...generally south of 40 degrees north
latitude. However...with a general consensus of there being a
shortwave and jet streak enhancement...even with models that have
dry quantitative precipitation forecast fields...will keep a slight chance of precipitation in the forecast.
With the dry and cold air advection...the precipitation type will be mainly
snow due to wet bulb effect with precipitation amounts between NAM and
sref...showing generally around three tenths of an inch or less...or
up to 3 inches of snow equivalently accounting for snow to liquid
ratio. This is for late Monday night through Tuesday evening. Again
though other models are completely dry and therefore these
probabilities remain very low.
The cold air mass settling in does not last that long. Monday has
temperatures near to slightly above normal. Tuesday through Thursday
is when the bulk of the cold air mass is in place with highs
hovering near to slightly above freezing on average. Near normal
temperatures return by late week.
Outside of the late Monday night through Tuesday evening
time frame...weather is mainly dry through Friday. Another frontal
system approaches late in the week with next chance for precipitation. Much
uncertainty though since this is day 8 of the forecast.
Therefore...these probability of precipitation are no higher than 30 percent with model run
fluctuations being more likely at this very late forecast time frame
with timing and placement differences.
Aviation /21z Saturday through Thursday/...
VFR conditions through tonight as high pressure moves off the middle
Light S/SW winds under 10 knots continue into tonight. Winds veer to
the west/SW Sunday morning.
Scattered-broken high clouds this evening...lowering overnight as a cold
front approaches from the west. MVFR ceilings in -shra likely towards
daybreak Sunday at kswf. Low probability of MVFR ceilings over city
terminals as -shra move east Sunday morning.
Outlook for 18z sun through Thursday...
Sunday afternoon...MVFR possible in -shra.
SW flow will increase tonight to 15-20 knots with gusts up to 25 knots.
This plus incoming swells of 2-3 feet should build combined ocean
seas to 5 feet east on the ocean east of Moriches Inlet...so Small Craft Advisory has been
issued there from 4-10 am Sunday. Could see an occasional 25-knots gust
farther west on the ocean near daybreak...but duration will be
short so Small Craft Advisory was not issued elsewhere.
There are also chances of Small Craft Advisory conditions Tuesday night and again
Wednesday night into Thursday...behind shortwaves with the cold air advection
and better mixing over the waters at these time frames. The Small Craft Advisory
chances are mainly for wind gusts mostly over the eastern waters.
Ocean seas on Thursday are forecast to reach 5-6 feet east of Fire Island
Inlet...but there is uncertainty with this.
quantitative precipitation forecast with the frontal passage on Sunday should range from 1-2
tenths of an inch. No significant precipitation of 1/2 inch or
Marine...Small Craft Advisory from 4 am to 10 am EST Sunday for anz350.