Area Forecast Discussion
Issued by NWS Upton, NY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KOKX 180234
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
934 PM EST Fri Nov 17 2017

.SYNOPSIS...
High pressure builds over the region overnight into early
Saturday. A warm front will lift to the north later Saturday,
then a strong cold front will approach Saturday night, and sweep
sweep eastward Sunday morning as strong low pressure passes to
the north. A few weather disturbances are possible later next
week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Winds continue to diminish as high pressure builds over the
region under mostly clear to clear conditions. Will be ideal
radiational cooling, however, a few knots of wind will make for
a trick low temperature forecast. The temperature at KFOK varied
from 35 to 26, and back up to 35 in a few hours as wind speeds
varied. The NYC metro will remain relatively warm as outlying
areas radiate. Minor changes to hourly trends and overnight
lows.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
Main concern will be an intensifying low moving into the Ohio
Valley Sat morning, then across the lower Great Lakes Sat night
and into the St. Lawrence Valley in Sunday. An associated warm
front will lift north of the area daytime Sat, with some showers
moving into the area from NYC north/west in the afternoon. The
pressure gradient between the departing high and the approaching
low will quickly tighten up, with S-SW winds gusting to 25-30
mph in most places, and as high as 35 mph across Long Island.

Main impacts ahead of and following a strong cold trailing the
low expected Sat night into Sunday, with S-SW winds increasing
further and a band of moderate to heavy showers sweeping across
with the front overnight. Models show fairly good low level
mixing with max boundary layer winds from 40-55 kt, highest
across eastern Long Island and SE coastal CT. Do not think the
full complement of these winds will mix down to the surface, but
gusts up to 35 mph are likely inland, 40-45 mph in NYC metro
and along most of the coastline, and 50-55 mph across eastern
Long Island. Confidence level in seeing winds over 60 mph is not
quite high enough to warrant a high wind watch for eastern
coastal sections, but this could change with later forecasts.
Will have to watch band of moderate to heavy showers with the
cold front itself for best low level momentum transfer on the
western fringe of the low level jet.

Winds could abate somewhat right after cold fropa, then should
pick up from mid morning into the afternoon after the passage of
a strong mid level vort max, via strong downward momentum
transfer of W-NW 40-kt H9 winds to the surface, with gusts up to
or just over 45 mph likely during this time frame.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
A broad area of high pressure will build into the region Monday
and Tuesday. This will produce fair weather. SuperBlend was
used for temperatures except for Monday night, where MEX was
used to better capture radiational cooling.

Wednesday remains a bit of a question. A cold front will be
approaching from the west. In addition, there remains the
suggestion that some semblance of a coastal low will develop.
The 12Z GFS is way off the Southeast coast and not a factor. The
12Z ECMWF is trending west and now produces a solid swath of
rain across the area. The forecast has been trended towards the
ECMWF, with low chances for precipitation included for all
areas. The rain would help to suppress high temperatures as
well. The cooler SuperBlend was used as a result.

The cold front comes through Wednesday night. The ECMWF is much
different than the GFS, which pours the cold air into the
region. The ECMWF keeps the coldest air locked to the north of
the area, most likely due to the dynamics of the strengthening
offshore low. A blend of the models was used, however depending
on how the pattern ultimately develops, Thanksgiving
temperatures could end up being roughly plus or minus 5 degrees
from the current forecast for highs. All solutions are dry for
the day however, followed by a continuation of the dry weather
on Friday.

The GFS does spin up a low along the subtropical jet and tracks
it east of the area on Friday. The ECMWF spins up something
similar on Saturday. This feature will need to be watched for
any westward trend.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
High pressure slides east of the region tonight into Saturday,
with a low pressure system approaching from the West.

VFR through Saturday morning, with increasing potential for
rain showers and MVFR or lower conds developing late Sat into
Sat evening.

Southerly winds increase Saturday morning into early Saturday
afternoon. SW winds 15 to 20 kt with gusts 25 to 30 kt likely
for coastal terminals Saturday aft/eve.

.OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY...
.Saturday Night...MVFR or lower conditions in -SHRA. LLWS
possible at night due to SW flow 40-50 kt at 2 kft AGL. S-SW
winds G25-35KT and occasionally higher for coastal terminals.
.Sunday...Conditions gradually improve to VFR with showers
ending by afternoon. NW windshift Sunday morning, with NW winds
G30-40KT through the day. Gusts diminish to 25-30 kt Sunday
evening.
.Monday...VFR. W-NW winds G20-30KT. Gusts diminish gradually at
night.
.Tuesday...Mainly VFR. MVFR possible late Tuesday night with
showers. SW winds G15-20KT.
.Wednesday...MVFR possible with showers. W-NW winds G15-20KT.

&&

.MARINE...
Winds and seas have diminished across the waters east of
Moriches Inlet and cancelled the advisory.

Winds and seas remain below advisory levels through the
overnight with winds and seas increasing Saturday ahead of an
approaching cold front.

A Storm Watch has been issued for the eastern ocean waters for
Sat night into early Sunday morning, for frequent gusts up to 50
kt in S-SW flow ahead of an approaching strong cold front. Gale
warnings have been issued elsewhere, beginning Sat afternoon on
the western ocean waters, and elsewhere Sat evening, with S-SW
winds increasing to 40-45 kt Sat night. W-NW gales should
continue after the cold frontal passage into at least Sunday
afternoon, and possibly into Sunday night especially on the
ocean.

SCA conds will follow into Mon, and are still possible mainly
on the ocean into Tue. Conditions may improve to below advy
criteria on Wed.

&&

.HYDROLOGY...
A band of moderate to locally heavy showers with a strong cold
frontal passage late Sat night should cause no more than
local nuisance impacts.

&&

.TIDES/COASTAL FLOODING...
Water levels will approach minor flood thresholds with Sat
morning high tide, but are expected to remain just below.

Storm surge guidance for Sunday morning high tide may to be on
the low side given the strength of southerly winds expected Sat
night into Sunday morning ahead of a cold front. But typically,
S/SW winds are not conducive to building surge.

There is a low probability of a surge of 1-2 ft Sunday morning.
If these surge levels develop, minor coastal impacts in a
strong SW/W flow would be felt mainly across eastern portions of
the Great South Bay into Moriches Bay. Elsewhere any impacts
would be brief and localized.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Gale Warning from 6 PM Saturday to 6 PM EST Sunday for ANZ330-
     335-338-340-345.
     Storm Watch from Saturday evening through Sunday morning for
     ANZ350-353.
     Gale Warning from 1 PM to 6 PM EST Saturday for ANZ350-353.
     Gale Warning from 1 PM Saturday to 6 PM EST Sunday for ANZ355.

&&

$$
SYNOPSIS...JMC/Goodman
NEAR TERM...Goodman/19
SHORT TERM...Goodman
LONG TERM...JMC
AVIATION...NV
MARINE...JMC/Goodman/19
HYDROLOGY...JMC/Goodman
TIDES/COASTAL FLOODING...NV



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.