Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
943 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/...
although high clouds are increasing across the region...it is not
enough to overcome the radiational cooling in some of the outlying
areas. Lowered min temperatures slightly in these areas to account for
this. Also...adjusted hourly temperatures to reflect current trends.
Otherwise...forecast is on track.
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.
Expecting the lows to be met by late this evening with steady to
slightly rising temperatures overnight as cloud deck increases in depth
with more middle level clouds moving as well as flow becoming more
southwest. The southwest flow will allow warm and moist air
Lows range from the low 30s in interior and rural sections to low
40s for much of NYC.
Also slightly adjusted probability of precipitation but overall they remain pretty much
the same as previous forecast.
Short term /6 am Sunday morning through Monday night/...
cold front should be accompanied/followed by some light rain
showers 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 showers 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 50.
Any lingering light rain showers 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 /03z Sunday through Thursday/...
high pressure moves east well off the middle Atlantic coast overnight.
A cold front moves through Sunday.
VFR conditions overnight with passing middle and high level clouds.
A few outlying airports though may observe fog with MVFR visibilities at
Light S/SW winds under 10 knots continue overnight. Winds veer to the
west/SW during the morning. Westerly winds around 10 knots are expected
during the afternoon along and behind the cold front.
The scattered-broken middle/high clouds lower overnight. MVFR ceilings in -shra are
likely towards daybreak at kswf. Low probability of MVFR ceilings over
city terminals as -shra move east during the morning. Higher
probability for MVFR ceilings in the afternoon...especially across
the coastal airports.
Outlook for 00z Monday through Thursday...
Sunday night-Thu...VFR. Low probability for light snow and sub-VFR
conditions during the day Tuesday.
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.