Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kokx 170000 
afdokx

Area forecast discussion
National Weather Service New York New York
700 PM EST Sat Nov 16 2019

Synopsis...
the center of strong high pressure shifts through northern New
England tonight and Sunday, then moves offshore Sunday night.
Coastal low pressure approaches on Sunday night and passes to our
southeast on Monday. A second weaker system is expected to develop
well offshore Tuesday night and move away during Wednesday.
High pressure will build by Wednesday night and settle nearby on
Thursday. A cold front will move through on Friday followed by
high pressure to begin next weekend.

&&

Near term /until 6 am Sunday morning/...
high pressure centered to our north shifts east later tonight.
Meanwhile, low pressure off the Carolina coast shifts NE. The
pressure gradient between the two systems will maintain somewhat
breezy conditions, and models agree with low level
moisture/clouds beginning to move in towards the coast late at
night. Satellite imagery continues to show clouds down off the
mid Atlantic coast being held at Bay for the time being. This
should continue for the remainder of this evening with high
pressure analyzed at 1037 mb holding strong during the first
half of tonight. Regardless of how far the clouds progress and
breezy conditions, low temperatures will still be about 10
degrees below normal in this cold air mass. Only slight
adjustments were made with respect to temperatures and dew
points for the remainder of this evening to match observations.

&&

Short term /6 am Sunday morning through Monday/...
high pressure moves across northern New England on Sunday while the
coastal storm off the Carolinas continues its path NE. Lower level
clouds will continue to push north through the forecast area
although areas northwest of the city could end up with at least partial
sunshine for a good portion of the day. Moisture will still be
shallow through the day, confined to below 875mb. Lift will be weak
at best, so will go with a dry forecast. High temperatures will be a
little warmer than it was was today, but still around 10 degrees
below normal.

The coastal low begins to travel in a more northerly direction
Sunday night as the associated cutoff low begins to interact with an
approaching longwave trough from the west and upper ridging weakens
over US. Still some model spread regarding timing and northwest progression
of pcpn, but overall it appears that it eventually becomes likely
east NYC with chance pops to the west. Rain will be the precipitation type
for most areas. For some of the northern zones, whether it be too
warm of an elevated warm nose aloft or a lack of moisture in the
dendritic growth zone, profiles would likely preclude the
possibility of snow. This leaves the potential of freezing rain and
maybe even some sleet for these areas, but with pops only at chance
here, will hold off on issuing any advisories.

The storm center then passes southeast of the 40n/70w benchmark on Monday.
Rain likely for most areas in the morning. Rain chances then
diminish somewhat in the afternoon, but is still likely over CT and
eastern Li.

Winds with this storm will be strongest late Sunday night through
Monday morning. Coastal sections during this time will have NE winds
20-25 mph with gusts up to 30-35 mph.

&&

Long term /Monday night through Saturday/...
it will be a progressive long wave pattern during the period. The
eastern US trough will redevelop sort to speak Monday night with
mean upper level troughing through Tuesday night. In the wake of low
pressure in the short term period, moisture will be lacking in the
mid levels. Therefore precipitation chances will generally lower
Monday night into Tuesday. The only fly in the ointment is with a
vort Max rounding the trough which will have some good positive vorticity advection with it
towards and after midnight late Monday night and into early Tuesday
morning. Guidance continues to hint at the potential for
measurable precip for northwestern zones during this time frame
as temperatures begin to cool. For the time being straying away
any measurable frozen precip for far northwestern zones, but it
will be close. Precip amounts would be very light if it does in
fact take place. This will have to be monitored with subsequent
forecast cycles as surface temperatures in these areas get
close to freezing early Tuesday morning. With mean upper level
troughing in place and a surface trough nearby think it is
prudent to maintain at least slight chance pops into early
Tuesday morning for the remainder of the area. With all profiles
above freezing any light or showery precip would be in the
liquid form, even well inland later in the morning. Despite a
good deal of clouds during much of Tuesday, much of the day
should go by generally dry with cool advection aloft beginning
to take hold. This along with a lack of mid level moisture
should limit precipitation despite the clouds Tuesday and
Tuesday night. Overall there will be a lack of meaningful
synoptic scale lift despite the upper level trough being in
place. A storm system will develop well offshore for Tuesday
night into Wednesday morning in response to the actual upper
level low, but will develop too late and too far to the east and
northeast to impact the region.

The 500 mb trough axis then pivots through by 12z Wednesday morning,
followed by transient height rises and ridging late Wednesday into
Thursday. This will lead to high pressure building in at the surface
from the southwest on Wednesday, with dry conditions expected during
the day Wednesday through the day on Thursday. The baroclinicity and
colder air will be lacking with this high pressure system, therefore
temperatures are expected to average near normal for the mid week.

By Thursday night a northern branch shortwave will dive into the
upper Midwest and Great Lakes. This will translate east and drag a
cold front through the region during Friday. The timing of the front
is difficult, but appears to be more likely during the first half of
Friday. Chance pops for late Thursday night into much of the first
half of Friday seems prudent at this time. A broad West Coast ridge
and broad eastern US trough then is forecast to follow into next
weekend. The source region will not be nearly as cold as previous
high pressure systems, therefore temperatures should be somewhat
seasonable into next weekend despite the mean upper level trough
into the northeast.

&&

Aviation /00z Sunday through Thursday/...
high pressure builds to the north and moves to the Canadian
Maritimes by Sunday. Low pressure off the southeast coast drifts
north tonight and Sunday.

VFR with only a few high clouds through tonight. Ceilings in the
3-4 kft range encroach from the south Sunday morning, with MVFR
ceilings expected to develop at the city and coastal terminals
between 13-16z.

Winds remain north/NE through the period, with speeds generally
12-18 kt (lighter at night, 6-12 kt). Occasional gusts to around
20 kt are possible through the overnight before becoming more
frequent again after 14z Sunday.

Outlook for 00z Monday through Thursday...
Sunday evening-Monday...MVFR cigs, with IFR conditions
possible late Sunday night/Monday morning. Chance of rain, with
chance of freezing rain well inland Sunday night into early
Monday morning. NE winds g20-25kt.
Monday night-Tuesday...mainly VFR with MVFR possible in a slight
chance of rain into Tuesday morning, then VFR.
Wednesday-Thursday...VFR. Northwest gusts 15-20 kt possible
Wednesday.

&&

Marine...
winds are expected to increase tonight in response to a re-tightening
pressure gradient ahead of an approaching coastal low. The low will
pass southeast of waters on Monday. Gales are expected on the ocean into
Monday, with Small Craft Advisory conds lasting through Monday on the rest of the
waters. Ocean seas eventually build up to 10-15 ft late Sunday night
into Monday morning.

Winds will continue to decrease Monday night with the non-ocean
waters having sub Small Craft Advisory conditions. Out on the ocean seas will be
decreasing, but will still remain elevated through Monday night and
into a good part of Tuesday. Therefore Small Craft Advisory conditions due to
elevated seas will likely continue into Tuesday out on the ocean.
Sub Small Craft Advisory conditions will continue for all waters late Tuesday through
early Wednesday, with marginal Small Craft Advisory conditions possibly returning out
on the ocean late Wednesday due to 4 to 5 foot seas as a northwest
wind increases late due to a tightening pressure gradient
due to building high pressure.

&&

Hydrology...
no hydrologic impacts are anticipated through the forecast
period.

&&

Tides/coastal flooding...
update was to convert the coastal Flood Watch to a coastal Flood
Warning for the Sunday high tide cycle for those South Shore Back
Bay locations of Nassau and southwest Suffolk.

However, expected tide levels were lowered slightly across the board
for the Sunday and Monday high tide cycles per latest guidance and
overall synoptic evaluation of storm, wind, etc. Fairly large spread
in ensemble guidance is noted, which leads to lower confidence in
exact tide level forecasts.

This timeframe is between full and new moons, which has helped as
large tidal departures are needed for coastal flooding due to
relatively low astronomical tides.

1-2 ft foot departures are needed for minor thresholds, and 2 to 3
ft is needed for moderate during the day. At night, astronomical
tides are about a foot lower, so only localized moderate coastal
flooding would be possible, with areas of minor and some locations
likely falling short of minor coastal flood benchmarks at night.

All of this is due to prolonged east-NE ocean gales through Monday,
accompanied by long period easterly swells of 9-13 ft by Sunday, and
10-15 ft on Monday. Winds do back to the north Sunday night and
Monday which may help keep departures down somewhat in spots (areas
where northerly winds push water away from the shoreline).

Elevated water levels with 8-12 ft breakers along the ocean
beachfront will result in beach erosion and flooding, with areas of
dune erosion and localized washovers likely during the times of high
tide Sunday into Monday. The North Shore of Long Island and the
north facing shoreline of the South Fork will also likely have beach
erosion and localized wave splashover issues due to rough waves as
well.

Perhaps some South Shore Back Bay locations may still hover at or
just below minor coastal flood benchmarks for the Monday night high
tide cycle. Otherwise the threat for coastal flooding will
generally subside Monday night into Tuesday.

&&

Equipment...
NYC National oceanic and atmospheric administration weather radio station kwo35 (162.55 mhz) is operating
at reduced power until further notice.

&&

Okx watches/warnings/advisories...
CT...coastal flood advisory from noon to 4 PM EST Sunday for ctz009-
010.
New York...coastal flood advisory from 9 am to 1 PM EST Sunday for nyz072-
074-075-178.
Coastal flood advisory from noon to 4 PM EST Sunday for nyz071-
073-078-176-177.
Coastal Flood Warning from 9 am to 3 PM EST Sunday for nyz080-
179.
Coastal Flood Watch from Sunday afternoon through Monday
afternoon for nyz080-179.
Coastal flood advisory from 11 am to 5 PM EST Sunday for
nyz079-081.
New Jersey...coastal flood advisory from 9 am to 1 PM EST Sunday for njz006-
106-108.
Marine...Small Craft Advisory until 6 PM EST Monday for anz330-335-338-
340-345.
Gale Warning until 1 PM EST Monday for anz353-355.
Gale Warning until 6 PM EST Monday for anz350.

&&

$$
Synopsis...jc/je
near term...jc/je
short term...jc
long term...je
aviation...Feb

National Weather Service Glossary of Abbreviations