Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 200534
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1234 AM EST Fri Jan 20 2017

.SYNOPSIS...
Weak high pressure remains over the region tonight. An upper
level disturbance will approach from the south on Friday, and
weaken as it moves across Friday night. High pressure briefly
returns on Saturday. Deepening low pressure moving across the
southern states on Sunday will reach the southern Mid Atlantic
region by Monday morning, while high pressure builds southeast
into the Canadian Maritimes. The low will intensify into a
significant coastal storm as it moves up the coast toward the area
Monday through Tuesday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Surface observations and satellite data continue to show extensive
cloud cover. Over the last few hours, stratus has filled back in
where it had scattered out earlier this evening. Will continue
with a mostly cloudy to overcast sky forecast. Have raised min
temperatures several degrees as clouds have kept temperatures
relatively stable. Some breaks in the clouds are possible towards
day break and could outlying areas drop several degrees.

Forecast low temperatures now range from the lower 30s inland to
the middle and upper 30s near the coast.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
High pressure ridge slides east early Friday morning, allowing
the next wave of low pressure to approach from the southwest.
Clouds increase Friday morning. As the wave nears the region,
POPs will gradually increase through the afternoon and evening.
All the forecast models are hinting at some kind of light to
moderate precipitation, so will continue to mention likely POPs.
QPF amounts will remain fairly light, with less than a quarter of
an inch of rainfall expected. The highest amounts are expected to
fall west of NYC. POPs gradually diminish after midnight as the
wave weakens and lifts north.

High temperatures on Friday continue about 5 degrees above normal
in the lower and middle 40s. Friday night, lows fall into the
30s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
A shearing shortwave will move ne of the region Sat with ridging
moving in at the surface and aloft. Weakening shower activity should
be pushing east Sat morning...but lingering cloud cover is likely
with weak waa under subsidence inversion. Temps likely run well
above seasonable in the upper 40s to lower 50s...with potential for
mid to upper 50s for NE NJ/NYC metro with breaks of sunshine.

Main focus is on a storm forecast to take shape as strong Pacific
jet energy crashes onshore the California coast Fri/Sat...allowing
an upper level system to close off over the southern plains this
weekend and then negatively tilt up the east coast Monday into
Tuesday. The result will be strong low pressure tracking through the
southern states this weekend...and then tracking up the eastern
seaboard towards the area Mon/Tue. Models in general agreement with
the synoptic fields...but spread exists in timing/intensity of the
closed upper low as it move up the coast...which is playing out in
model spread on track/speed of the surface low Mon/Tue.
SBU ensemble sensitivity points towards a strong wave packet
emanating from shortwave energy developing off the eastern Asia
coast as the determining factor. Have stayed close to ensemble
means with forecast...with general trends of low pressure
tracking a bit farther se and slower than 24 hours ago.

Potential exists for multiple impacts including strong winds, heavy
rain (wintry mix NW) and minor to locally moderate coastal flooding,
with likelihood of occurrence in that general order. In terms of
heavy precip...PWATs of 3-4 stds above normal are being signaled as
the system taps into tropical connection to the Caribbean and
Eastern Pacific. The potential for 1 to 3 inches of qpf with higher
amounts continues.

Based on strong dynamics and se trend towards a track over or just
se of LI...potential for thermal profiles to diabatically cool to
near freezing and result in a rain/snow mix well N&W of NYC for a
portion of this event...with even a period heavy wet snow across NW
hills. Still too much uncertainty at this point to talk
amounts...but at least a low potential exists for an accumulating
wet snow for the NW hills.

In terms of winds...GEFS signaling an easterly
llj 4-5 std above normal. EPS probabilities for wind gusts over 50
kt continue to run in the likely range Mon/Mon night for the
immediate coastline, and the extended 00z/12Z GFS/ECMWF MOS guidance
indicate sustained winds 25-30 kt along the coast and in the higher
interior elevations. This signals moderate potential for wind
advisory conditions for the coastal and low potential for high wind.
See coastal flood sections for potential coastal flood impacts.

Gradually improving conditions Tue aft into Tue night as the upper
low pivots ne and low pressure tracks up the New England coast.

&&

.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
High pressure builds in from the west overnight and then moves
offshore on Friday as a warm front approaches from the south.

Ceilings at or below 3 kft much of the time overnight into early
Friday morning. VFR conditions will return briefly for the mid to late
morning on Friday before MVFR conditions return late Friday afternoon
and early Friday evening with light rain likely.

N-NE winds dropping off overnight to near 5 kt or less. A return
E flow develops late Friday morning at less than 10 kt. The winds
then veer to the SE by the late afternoon and will remain under
10kt.

.OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY...
.Friday night... MVFR and IFR in -RA, with a period of LIFR possible
at some terminals mainly after 3z.
.Saturday-Saturday night...MVFR or lower possible early Saturday
morning, followed by VFR for the late morning and into Saturday
afternoon and night.
.Sunday-Sunday night...MVFR or lower in -RA, mainly late Sunday
afternoon through Sunday night. Moderate rain develops at night.
NE gusts 20-25 kt by late Sunday afternoon and evening. NE gusts
30-40 kt Sunday night.
.Monday...IFR with moderate to heavy rain and strong E-NE winds.
NE gusts 35-45 kt.
.Tuesday...Rain tapering off with improving ceilings. Gusty NW
winds possible later in the day.

&&

.MARINE...
Easterly swell has slowly subsided, but sill seeing significant
wave heights at 44025 close to 6 ft. Since the other buoys are
still close to 5 ft, will continue with the Small Craft Advisory
for Hazardous Seas.

Winds and seas should then remain below SCA levels on all
waters through Friday night.

An intensifying storm moving up the coast early next week will
likely bring easterly gales to all waters from Sunday night into
Monday night...with storm force wind gusts may be possible on the
ocean and eastern most Long Island Sound. If these winds come to
fruition...15 to 20 ft waves possible over the ocean waters...with
4 to 8 ft on LI sound.

&&

.HYDROLOGY...
No significant precipitation is expected through Saturday night.

Potential for significant rainfall of 1 to 3 inches, with locally
higher amounts with a coastal storm early next week. If high end
rainfall amounts are realized...this will present a threat for minor
areal flooding...including small stream flooding. Rises on larger
rivers would be likely...but at this point the potential for minor
flooding appears slight.

&&

.TIDES/COASTAL FLOODING...
A strong coastal storm may cause minor to locally moderate coastal
flooding if its highest surge coincides with the early morning high
tide cycles either Mon or Tue, which is the higher of the two daily
high tide cycles. Stevens ensemble guidance is showing potential for
surge building to 3 to 4 ft on Monday.

Surge needed to cause minor coastal flooding is about 1.5-2.5 ft on
the Long Island South Shore back bays, and 2.5-3.0 ft elsewhere.

Surge needed to cause moderate coastal flooding is about 2.5-3.0 ft
on the Long Island South Shore back bays, and 3-4 ft elsewhere.

The other concern will be for significant beach erosion from long
period easterly swells of 10-15+ ft Mon into Tue. Localized washover
cant be ruled out if higher surge values are realized.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory for hazardous seas until 6 AM EST early
     this morning for ANZ350-353-355.

&&

$$
SYNOPSIS...BC/NV
NEAR TERM...JMC/DS
SHORT TERM...BC
LONG TERM...NV
AVIATION...JC/JE
MARINE...BC/JMC/NV
HYDROLOGY...BC/NV
TIDES/COASTAL FLOODING...


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