Scientific Forecaster Discussion
fxus61 kokx 210308
Area forecast discussion
National Weather Service New York New York
1008 PM EST Tue Nov 20 2018
high pressure briefly builds from the southwest tonight before an
Arctic cold front approaches on Wednesday. This cold front moves
through Wednesday evening with high pressure building in for
Thursday. High pressure moves off into the Atlantic Ocean
Friday night. A low pressure area approaches Saturday and moves
across Saturday night into early Sunday. Weak high pressure
follows that and then another low moves in for early next week.
Near term /until 6 am Wednesday morning/...
on the heels of a shortwave trough that passed through this
evening, there will be a quick shot of cold advection with
occasional wind gusts up to 20 mph. A few minor adjustments were
made to forecast based on latest observations.
Deepening low pressure near Nova Scotia tracks NE overnight as
high pressure builds to our south and west. Drier air advects
into the region under a breezy westerly flow.
Clearing skies and diminishing winds will allow temperatures to
fall into the 20s inland/Pine barrens of Li and lower 30s
closer to the coast.
Short term /6 am Wednesday morning through Wednesday night/...
the main story for Wednesday will be the approaching Arctic cold
front and anomalous upper closed low/trough digging towards New
The day should start out mostly clear and chilly, but clouds begin
to increase into the afternoon as the front approaches. There is
good agreement among the models for the cold front to move across
the area in the evening. High resolution models including the
namnest and extended hrrr hint at a broken band of snow showers
along the boundary as the front moves through. Think this is
reasonable as there will be some weak instability in the low levels
as the cold air begins to move into the area. Probabilities for snow
showers will be held down in the slight chance range for now. The
timeframe for these snow showers looks to be from around 21-23z
across the northwest interior moving eastward thereafter from 23-
03z. Wind gusts in the afternoon and evening look to be 20-30 mph,
but gusts could briefly end up higher along the frontal passage and
in any snow shower.
High temperatures will continue below normal in the low 40s inland
and the middle 40s closer to the coast.
Significant cold air advection commences Wednesday evening behind
the front and as the deep upper low shifts over northern New
England. Anonymously cold and unseasonable air will quickly
overspread the region Wednesday night into Thursday morning. 850 mb
temperatures go from -8 to -12c at 00z Thursday to -16 to -19c by
day break Thursday morning. These readings are near the minimum
observed for November 22 (-17c) based on sounding climatology from
Storm Prediction Center.
Surface temperatures will start out in the 30s in the evening and
drop considerably through the night with temperatures in the teens
inland and near 20 in the NYC Metro and Long Island by day break.
Blustery northwest winds will make it feel like the single digits early
Long term /Thursday through Tuesday/...
polar jet will be across the region Thursday through Friday with
more of a split jet structure across the region for the weekend.
Subtropical jet strengthens and approaches the region late in the
weekend. This moves into the region early next week.
At the surface, very cold airmass builds in for Thursday through
Friday as strong Canadian high pressure builds in. Strong subsidence
will keep dry conditions during this time period along with
temperatures well below normal. Highs forecast on Thursday stay in
the 20s with highs near 30 forecast on Friday. Breezy conditions
Thursday will decrease Thursday night into Friday with a decrease in
the pressure gradient.
A more unsettled weather pattern unfolds thereafter. Troughs move in
late Saturday into Sunday and early next week with accompanying
low pressure systems at the surface. The airmass will be
moderating Friday into the weekend so with a more southerly flow
Friday night into Saturday, this will moderate temperatures with
highs Saturday in the mid 40s to near 50. The timing of the system
with abundant clouds Saturday night and onshore flow is expected
to keep temperatures in the upper 30s to mid 40s. Lower 50s
forecast Max temperatures Sunday will be followed by mid 30s to
low 40s min temperatures Sunday night as well as mid 40s to low
50s for Max temperatures Monday. So, the two systems moving in for
the long term period look to be mostly stratiform rain.
Please see our social media platforms for a graphic displaying
the top 5 coldest high temperatures and top 5 coldest low
temperatures for the Thanksgiving Holiday at Central Park.
Aviation /03z Wednesday through Sunday/...
high pressure builds in from the west tonight. An Arctic front
passes late Wed.
Mainly VFR through the taf period. A brief period of MVFR or lower
possible 21z Wed thru 2z Thu in isold-sct shsn.
Diminishing northwest winds tngt, then speeds increase again during
the day Wed, and particularly behind the Arctic front late.
Outlook for 00z Thursday through Sunday...
Wednesday night...VFR. Low chance MVFR or lower in shsn in the eve.
West-northwest winds g20-30kt.
Wednesday night-Thursday...VFR. Northwest winds g25-30kt.
Saturday...VFR early...followed by possible MVFR in the afternoon.
Sunday...MVFR early...VFR in the afternoon.
marginal Small Craft Advisory conditions on the ocean, eastern Li sound and
eastern bays overnight. Ocean seas may build to near 5 ft
tonight. Winds may briefly weaken early Wednesday morning before
increasing on all waters late morning into the afternoon ahead
of the cold front. Ocean seas will build to 5 to 7 ft in the
afternoon and evening as well. Headlines remain in place tonight
but have adjusted the start time for the Small Craft Advisory on the New York Harbor,
western Li sound, and Great South Bay to 15z Wednesday.
The cold front crosses the waters Wednesday evening with the
potential for gales on the ocean, eastern Li sound and eastern Li
bays. Confidence in gales occurring is not high enough to
convert the watch over to a warning at this time, but have
extended the Small Craft Advisory on the New York Harbor, western Li sound and Great
South Bay through Wednesday night. The gale watch has been
extended into Thursday as gales remain possible.
Gales will be probable across the eastern and ocean waters to start
the long term period Thursday with otherwise widespread across Small Craft Advisory
winds. Winds decrease Thursday night but still will be mainly Small Craft Advisory
levels. Small Craft Advisory winds return Saturday night for the ocean. Otherwise,
Friday through Sunday night, below Small Craft Advisory winds are forecast.
Ocean seas are forecast in the Small Craft Advisory range Thursday into Thursday
night as well as Saturday night through Sunday night. Otherwise,
seas are below Small Craft Advisory.
no significant hydrologic impact expected through the rest of
record low temperatures for Thu Nov 22:
Central Park.....13 (1880)
Record low maximum temperatures for Thu Nov 22:
Central Park.....23 (1880)
Record low temperatures for Fri Nov 23:
Central Park.....14 (1880)
*also occurred in previous years
NYC Central Park winds are out of service until further notice.
Loss of data is due to a severed cable, parts are on order.
NYC National oceanic and atmospheric administration weather radio station kwo35 (162.55 mhz) will remain off
the air for an extended period of time.
Marine...Small Craft Advisory from 10 am Wednesday to 6 am EST Thursday
Gale watch from Wednesday evening through Thursday afternoon
Small Craft Advisory until 6 PM EST Wednesday for anz330-340-