Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 230253

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

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.


Main concern for tonight continues to be the development of fog
and low clouds. A light southerly flow over the area tonight
will gradually increase low level moisture. Cooling surface
temperatures 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. Fog has already started as of 02z
for a few spots over eastern Long Island. with low stratus being
more widespread. Have noted this signal in BUFKIT profiles from
the HRRR, RAP and NAM-4km, but the bulk of fog development may
not occur until after midnight. The fog and low stratus should
then expand northward towards into the early morning hours. How
low widespread visibilities ultimately get is uncertain at this
time, but widespread dense fog is a possibility, mainly near the
coast and especially over Long Island. Have issued an SPS for
Suffolk County to address dense fog being at least patchy.

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


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.


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

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.


High pressure off the Mid Atlantic coast will produce a weak onshore
flow across the terminals overnight through Thursday.

IFR to LIFR ceilings along with MVFR to IFR fog has developed across
Long Island this evening. Other areas were VFR. Fog and stratus is
expected to expand north and west with the NYC area terminals
becoming MVFR and possibly at times IFR. And after 06Z coastal, y
Connecticut into the lower Hudson Valley becomes MVFR to IFR.

MVFR to IFR remains into Thursday morning with conditions improving
to VFR by late morning into the afternoon. Along the coast possible
that conditions remain MVFR through much of the afternoon. Timing of
improvement is uncertain at this time.

Conditions lower once again after 23Z Thursday.

Light and variable, to calm, winds at all terminals overnight, then
becoming S-SW Thursday.

.Thursday night-Saturday...MVFR to IFR in stratus and fog.
Likely improving to VFR during the day Friday before lowering
again Friday night. Chance of light rain or drizzle.
.Saturday night...MVFR likely with rain. Gusty S winds becoming NW.
.Sunday...VFR...Gusty NW winds.
.Monday...VFR early...becoming MVFR. Chance of rain or snow.


Might need to eventually issue a dense fog advisory for tonight
should it become more obvious that dense fog becomes more

Otherwise, 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.


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




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