Scientific Forecaster Discussion
fxus61 kokx 150532
Area forecast discussion
National Weather Service New York New York
1232 am EST Fri Dec 15 2017
high pressure builds into the area tonight then quickly shifts
offshore on Friday as an area of low pressure develops off the
mid Atlantic coast. Low pressure quickly departs eastward on
Saturday, with high pressure briefly building in again in its
wake. A series of weak low pressure and frontal systems will
pass through mid week.
Near term /until 6 am this morning/...
forecast is on track.
The pressure gradient will gradually relent tonight as high
pressure builds into the region from the west. Strato-cu has
quickly dissipated in the subsident environment, with mainly
just some jet induced cirrus working in overnight. The result
should be favorable radiational cooling overnight, with the
remaining snow pack aiding in temperatures across outlying area
radiating into the lower teens to single digits, generally about
10 to 15 degrees below climatological normals.
Short term /6 am this morning through 6 PM Saturday/...
the persistent blocking pattern will gradually begin to break
down on Friday with a subtle eastward shift to a large scale
East Coast upper trough, while upstream low pressure flattens a
dominant ridge on the West Coast.
Phased vorticity maximums will push eastward, allowing a surface
low to intensify off the Carolina coast before ejecting
eastward. Across the area, temperatures will remain below
normal, largely below freezing, with increasing cloud cover
through the day as the phased vorticity maximums approach.
Although the heaviest snowfall will remain well south of the
area, mid-upper level lift/saturation will gradually increase
into the evening, with any developing precipitation aloft
subsequently saturating low levels enough to produce at least a
dusting of snow along the coast.
A slight northward shift noted in the 18z guidance, which if
trend continues would increase potential for a light measurable
snow across at least southern and eastern portions of the tri-
state, but at this point only a 1 in 10 chance of seeing more
than an inch of snowfall.
Cloud cover decreases again Friday night as the system pushes
east of the area, while winds gradually increase as the pressure
gradient increases ahead of building high pressure. Low
temperatures are already forecast to be well below normal, but
could drop further depending on the exact timing of clearing
skies and increasing winds.
Long term /Saturday night through Thursday/...
a progressive pattern in place across the country for the long term
period. High pressure builds to the south on Saturday as a coastal
low remains well to the southeast of the area. As the low exists, west-
northwest winds increase, especially across Long Island and coastal CT
where the low level jet moves across. Below normal temperatures,
combined with gusty winds, will keep wind chill values in the low
20s during the day.
The forecast becomes more uncertain on Sunday night into Monday as a
weak warm front moves towards the region. While models are in good
agreement regarding upper level energy, there is still disagreement
amongst precipitation amounts. However, with winds shifting to the
SW expecting a period of rain/mixed precipitation overnight into
Monday. Confidence still remains low based on the differences in
By Monday temperatures return to near seasonal norms for mid
Thereafter, models in fairly good agreement with a northern stream
trough approaching the region on Tuesday, but differences exist in
the amount of interaction with southern stream energy/moisture.
Primary low pressure system appears to ride through Quebec/Ontario
with trailing cold front approaching the region, but precip
coverage amounts will be dependent on the aforementioned
southern stream interaction. Thermal profile suggests precip
would be a wintry mix transitioning to rain, but predictability
at this point is low.
Upper trough swings through the NE Tue night into Wed with a
glancing shot of modifying Arctic air in the wake of the cold front
Aviation /06z Friday through Tuesday/...
high pressure builds in through Friday morning with VFR
conditions. Then, weak low pressure moves northeast of the mid-
Atlantic coast. This will bring some snow Friday afternoon into
Friday evening with associated MVFR/IFR conditions. There is a
potential for a light snow accumulation up to 1-2 inches. VFR
returns by late Friday night.
Wind gusts have subsided. West-northwest flow near 10 kt will decrease
further overnight before becoming more west-southwest-west at 5-10 kt on
Outlook for 06z Saturday through Tuesday...
Friday night...VFR. A few west winds g20kt late.
Sat...VFR. West-northwest winds g20-25kt daytime.
Sun...VFR most of the time. Chance MVFR in -ra/-sn late at
Monday...chance MVFR -ra for coastal terminals, light wintry mix
with MVFR/IFR inland early and at night.
Tuesday...MVFR possible. Slight chance of mainly -ra.
winds are slower to diminish than guidance is indicating, thus
have extended the Small Craft Advisory from Sandy Hook to Fire Island Inlet
through 10z. They may come down over the next hour or two
though. Winds and seas will fall below Small Craft Advisory levels on the ocean
waters by daybreak as high pressure builds into the area.
Tranquil conditions will then persist into Friday, before winds
and seas increase to Small Craft Advisory levels again Friday night with the
departure of a low pressure system to the south and east. These
conditions will persist into Saturday night, followed by a
better chance of Small Craft Advisory or possible gales in the wake of a midweek
no significant hydrologic impacts expected.
NYC National oceanic and atmospheric administration weather radio station kwo-35 (162.55 mhz) is off the
air for an extended period of time.
Marine...Small Craft Advisory until 5 am EST early this morning for
Small Craft Advisory until 7 am EST this morning for anz350-