Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 222029
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
329 PM EST Wed Feb 22 2017

.SYNOPSIS...
High pressure over the western Atlantic will influence the weather
across the Tri-State through Thursday. A mild, damp, spring-like
pattern Friday and Saturday will give way to a more seasonal
pattern for the beginning of next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Some breaks in the clouds are now occurring as the middle levels dry
out. Weak shortwave energy has moved to the east and the poorly
defined boundary has dissipated. Warmest temperatures of the day
will occur into the late afternoon before dropping after sunset.

Main concern for tonight is the development of fog and low clouds. A
light southerly flow over the area tonight will gradually increase
low level moisture. Cooling surface temperatures with loss of
heating in combination with weak warm advection above the surface
will create a steepening temperature inversion. Moisture will become
trapped beneath this inversion overnight into the early morning
hours. Areas of fog and low stratus will likely result from these
conditions. Have noted this signal in BUFKIT profiles from the
HRRR, RAP and NAM-4km, but it could end up occurring around or
after 09z. The fog and low stratus should then expand northward
towards into the early morning hours. How low visibilities
ultimately get is uncertain at this time, but dense fog is a
possibility, mainly near the coast.

Low temperatures will be in the upper 30s inland and low to mid 40s
along the coast.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
High pressure will remain across the western Atlantic, pumping a
warm and moist southerly flow around it towards the local area.
Aloft, a split flow pattern continues with core of northern stream
well to our north and a slow moving upper low across the southeast
states within the southern stream.

Areas of fog and low stratus start the day on Thursday. The first
forecast challenge is the duration. The fog should lift through the
morning hours, but the stratus could hang on into the early
afternoon. This creates another challenge with regards to
temperatures. There is high confidence in seeing unseasonably warm
temperatures for this time of year. However, how quickly clearing
occurs will be important to how warm it gets away from the coast.
Highs should be able to reach the middle and upper 60s north and
west of the city where clearing occurs the quickest. In the NYC
metro, readings will be in the lower to middle 60s. Further east
across southern Connecticut and Long Island, temperatures will be
held in the 50s to near 60 due to onshore flow. If the clouds clear
quicker, then highs could end up warmer and some records could be
broken. If clouds hang on longer, then highs could be held down
several degrees from current forecast.

For Thursday night, a weak boundary tries to move into the area from
the north. The boundary likely stalls nearby overnight and acts as a
focus for some areas of drizzle and fog development in a continued
moist environment. There is also the chance of some rain along this
boundary. Lows continue mild in the 40s to near 50 degrees.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Not much change to the forecast for Friday through Sunday. The
operational models are catching up with the conceptual model of
light rain and drizzle Friday night into Saturday. The timing of the
cold frontal passage has been narrowed down to the first part of
Saturday night, with the GFS now latching onto the ECMWF timing.

The models are showing some weak elevated instability in the
vicinity of the cold frontal passage. It would be preferred however
to have some solid upper level divergence to get thunderstorms
going. As a result, they have been left out of the forecast for now
based on the progged position of the upper jet in the 12Z data. If
the jet streak ends up further south, they may need to be
reintroduced to the forecast.

There remain some questions for Monday. The GFS continues to bring a
system through with some snow and rain. The ECMWF is now clipping
the southern portion of the forecast area. Considering the system is
currently near Barrow, Alaska, model agreement is actually pretty
good. Chances for precipitation have been set at 30 percent for this
event.

The pattern then shifts again with southwesterly flow aloft
developing Tuesday and Wednesday. The timing of the warm front and
associated low are progged in the Tuesday night and Wednesday period
per the model consensus, so chances for rain have been included in
the forecast.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
High pressure off the Mid Atlantic coast will produce a weak
onshore flow across the terminals tonight and Thursday.

VFR conditions will give way to MVFR or lower after sunset as fog
and/or low stratus begin to develop. It now appears that MVFR
visibilities initially develop after 03Z at coastal terminals before
spreading inland around 06Z. All guidance suggests the best chance
for IFR or lower conditions appears to be between 09-15Z before
conditions gradually improve during the late morning.

Light and variable winds at all terminals tonight before becoming SW
on Thursday.

     NY Metro Enhanced Aviation Weather Support...

Detailed information, including hourly TAF wind component forecasts,
can be found at: http:/www.weather.gov/zny/n90

KJFK TAF Comments: Uncertainty exists in the timing and areal
extent of developing IFR Conditions tonight.

KLGA TAF Comments: Uncertainty exists in the timing of developing
and areal extent of IFR Conditions tonight.

KEWR TAF Comments: Uncertainty exists in the timing of developing of
MVFR or lower conditions tonight. Chance of IFR conditions.

KTEB TAF Comments: Uncertainty exists in the timing of developing of
MVFR or lower conditions tonight. Chance of IFR conditions.

KHPN TAF Comments: Uncertainty exists in the timing of developing
IFR Conditions tonight.

KISP TAF Comments: Uncertainty exists in the timing of developing
IFR Conditions tonight.

.OUTLOOK FOR 21Z THURSDAY THROUGH MONDAY...
.21z Thursday-Saturday...MVFR or lower in stratus and fog. Chc of
light rain or drizzle.
.Saturday night...MVFR likely with rain and a slight chance of
thunderstorms early. Gusty S winds becoming NW.
.Sunday...VFR...Gusty NW winds.
.Monday...VFR early...becoming MVFR. Chance of rain or snow.
Winds becoming S-SW around 10 kts.

&&

.MARINE...
High pressure over the western Atlantic brings a weak pressure
gradient and rather tranquil conditions to the local waters through
Thursday night. Southerly wind gusts on the ocean could increase to
close to 20 kt Thursday afternoon and evening. A southerly swell may
also bring ocean seas to near 4 ft Thursday night. Otherwise, sub-sca
conditions are expected.

Winds and waves will remain below Small Craft Advisory levels
Friday. Conditions will deteriorate Saturday, with criteria likely
to be achieved Saturday night after a cold frontal passage. Small
Craft Advisory conditions are then likely on Sunday, and possible on
Monday. Winds and seas improve on Tuesday.

&&

.HYDROLOGY...
No hydrologic impacts are expected through Friday. Around an
inch of rain is possible Saturday and Saturday night. Measurable
precipitation is possible Monday and again Wednesday of next
week.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

&&

$$
SYNOPSIS...12/DS
NEAR TERM...DS
SHORT TERM...DS
LONG TERM...12
AVIATION...IRD
MARINE...12/DS
HYDROLOGY...12/DS


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