Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kokx 160117 
afdokx

Area forecast discussion
National Weather Service New York New York
817 PM EST sun Dec 15 2019

Synopsis...
high pressure briefly builds over the region tonight, then
drifts offshore Monday. A low pressure system approaches the
region Monday and impacts the region Monday night and Tuesday
before moving northeast to the northern Atlantic Tuesday night
into Wednesday. A polar front approaches Wednesday and moves
across Wednesday night. Canadian high pressure moves in for
Thursday through Friday night. The high lifts farther north of
the area next weekend with possible close approach of offshore
low pressure.

&&

Near term /until 6 am Monday morning/...
just made some minor adjustments to hourly temperatures,
dewpoints, and cloud coverage to better match observed trends.
Forecast overall is on track.

High pressure will build over the region tonight with dry
conditions expected. Winds will gradually weaken, becoming light
and variable west of NYC, and less than 10kt elsewhere from the
west. This high will keep a warm front south of the area
tonight. Lows will fall into the 20s and 30s.

&&

Short term /6 am Monday morning through Monday night/...
Monday starts off with high pressure over the region, which
will gradually shift to the east through the day. Meanwhile, a
warm front will remain south of the area with precipitation
gradually developing along the front.

The 12z forecast guidance, along with some of the early 18z
guidance shows that much of the precipitation will struggle to
move into our area as it will struggle with the dry air from the
departing high to the northeast. Thinking that if any
precipitation falls during the day on Monday, it will be light
and mainly in the form of flurries or light snow showers.

By Monday evening, the high pressure moves far enough east to
allow precipitation to push its way across the area from south
to north. Even with the high nearby, signals of cold air damming
will keeping cold air in place across the northern tier for
much of Monday night.

In terms of precipitation type, the precipitation should start
off as snow everywhere with wet bulb cooling, then quickly
transition to a rain/snow mix then to all rain by 06z Tuesday
across NYC, Long Island and Metro New Jersey. Elsewhere, a prolonged
period of snow and a wintry mix can be expected, with snowfall
totals ranging between 1-2 inches and ice accumulations up to 2
tenths of an inch. As a result, have issued a Winter Weather
Advisory for much of our northern zones where the highest
confidence is for the snow/ice combo. For now, have left coastal
CT out of the advisory as confidence is not as high with ice
accumulations and more rain may occur. The storm total ice
forecast is showing any measurable ice accumulations to remain
across the interior and this is where there is higher confidence
of obtaining ice accretion. Stay tuned for any additional
updates as changes to the forecast may be necessary depending on
the timing of the precipitation and the rain/snow line.

Temperatures on Monday will be in the 30s. Monday night, lows
will be in the 20s and 30s, with lows occurring very early in
the tonight period, and slowly warming through the night.

&&

Long term /Tuesday through Sunday/...
first of all, the Winter Weather Advisory will be ongoing for
interior parts of the region with some additional snow and ice
accumulations during Tuesday. All precipitation tapers off Tuesday
evening.

Second half of the storm event for Tuesday with the low center
moving just south of the local area. 850mb freezing line will be
north of the entire County Warning Area during the day and then start to move
farther southward with cold air advection on the backside of the low
as it moves farther east of the area late afternoon into the
evening.

The second half of the storm event will feature a continuation of a
wintry mix across the interior including some additional freezing
rain while the coast will remain as plain rain as dewpoints are
expected to be above freezing. At the end of the event late
afternoon into early evening, there could be a brief window of a
rain snow mix getting farther southward towards the coast, but only
minor accumulations of less than an inch of snow expected and that
is across the interior with no snow accumulation expected for the
coast. Highs Tuesday will be from the lower 30s across the interior
to the upper 30s to lower 40s along the coast.

Conditions will become drier Tuesday night with weak high
pressure from the southwest briefly building in. Clouds will
decrease and northwest winds will lighten. Lows Tuesday night are
expected to be in the mid to upper 20s as winds will stay up
enough to prevent ideal radiational cooling.

A key part to the forecast is temperatures for these went with
consraw for temperatures Tuesday and transitioned from consraw to a
blend of consmos and nam12 for Tuesday night.

For the rest of the long term, that high pressure area from the
south and west will quickly way on Wednesday to an approaching polar
front. This will be accompanied aloft by a very strong mid level
shortwave as diagnosed from a strong positive vorticity Max.

This will bring some snow shower activity, slight to low end chance
Wednesday into Wednesday night. Low confidence on timing and
location of snow showers. Not expecting much if any snow
accumulation. Much colder airmass moves in Wednesday night and
lingers through Friday night. Temperatures are expected to be well
below normal. Northwest flow will be gusty Wednesday night into Thursday
night which will help advect in colder air.

For next weekend, the high lifts farther northward. The airmass
across the region will moderate. Models convey a vast array of
solutions regarding low pressure offshore and its track. A lot of
uncertainty in the local forecast in this timeframe.

&&

Aviation /01z Monday through Friday/...
high pressure will briefly build over the region tonight, then
drift offshore Monday. Low pressure will approach on Monday.

West-northwest winds should gradually diminish to under 10 kt overnight,
then as the high passes east become light SW-S in the afternoon,
then NE-east in the evening.

Clouds should start to lower/thicken late tonight into Monday.
Timing of precip and MVFR conds uncertain and could trend later
than fcst.

Outlook for 00z Tuesday through Thursday...
Monday night...IFR or lower likely. For the NYC Metro and
coastal terminals, wintry mix gradually changing to plain rain
late, though ewr/kteb/kbdr could see freezing rain linger into
the early Tue morning push. Khpn/kswf wintry mix, including
freezing rain.
Tuesday...IFR or lower conds. Wintry mix, possibly changing
back to all snow at kswf before ending. Rain at NYC/New Jersey Metro
and coastal terminals, possibly changing to wintry mix before
ending late. North winds g20kt in the afternoon.
Tuesday night...VFR. Northwest winds g20kt NYC metros/kisp mainly eve.
Wednesday...VFR. Northwest winds g25kt mainly afternoon.
Thursday and Friday...VFR.

&&

Marine...
gales have subsided across most waters except for the ocean east
of Fire Island Inlet. That Gale Warning remains until 10 PM
tonight. Other gales were replaced with Small Craft Advisory. The Small Craft Advisory for the New York
Harbor, western Long Island Sound, South Shore bays GOES until
midnight while the Small Craft Advisory for eastern Long Island bays and eastern
Long Island Sound as well as the ocean west of Fire Island Inlet
GOES until 6 am Monday.

Ocean seas will be a bit slower to respond with residual S/southeast
swells, but should fall below Small Craft Advisory from west to east through
Monday morning. Sub-Small Craft Advisory conditions are expected for much of
Monday and Monday night.

Small Craft Advisory seas return on the ocean Tuesday with otherwise sub-Small Craft Advisory
conditions all across the rest of the waters. Winds are below Small Craft Advisory
criteria. Small Craft Advisory ocean seas remain through Thursday and then decrease
to below Small Craft Advisory Thursday night and remain below Small Craft Advisory Friday into Friday
night. For the wind gusts, Small Craft Advisory wind gusts expected Tuesday night
across mainly the ocean waters. Wind gusts return to Small Craft Advisory levels on
the ocean Wednesday afternoon and all waters have at least Small Craft Advisory level
winds Wednesday night through Thursday with potential for gales on
the eastern and ocean waters during this timeframe. Small Craft Advisory levels gusts
forecast on the eastern and ocean waters Thursday night. Winds are
mainly below Small Craft Advisory Friday into Friday night.

&&

Hydrology...
remaining flooding concerns are for the larger Stem rivers in
CT with a combination of the recent rainfall and melting snow
to the north.

Another significant precipitation event is likely Monday through
Tuesday, with liquid equivalent quantitative precipitation forecast of 0.5 to 1.00 inches
possible. There is uncertainty in this amount given uncertainty
in the track of the low and frontal positions.

No significant widespread precipitation expected from Tuesday night
Onward through the rest of the forecast.

&&

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

&&

Okx watches/warnings/advisories...
CT...Winter Weather Advisory from 6 PM Monday to 6 PM EST Tuesday
for ctz005>008.
New York...Winter Weather Advisory from 6 PM Monday to 6 PM EST Tuesday
for nyz067>070.
New Jersey...Winter Weather Advisory from 6 PM Monday to 6 PM EST Tuesday
for njz002-103.
Marine...Small Craft Advisory until midnight EST tonight for anz335-338-
345.
Small Craft Advisory until 6 am EST Monday for anz330-340-355.
Gale Warning until 10 PM EST this evening for anz350-353.

&&

$$
Synopsis...BC/jm
near term...BC/jm
short term...BC/jm

National Weather Service Glossary of Abbreviations