Scientific Forecaster Discussion
fxus61 kokx 180934
Area forecast discussion
National Weather Service New York New York
434 am EST Sat Nov 18 2017
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
Near term /until 6 PM this evening/...
ridge axis shifts to the east this morning as a longwave trough
advances through the plains and will reach the Midwest/Ohio
Valley by evening. Clouds will rapidly increase this morning,
and models are in good agreement that overrunning rain
associated with an approaching warm front holds off until aftn.
Best chances will be north and west of NYC until late. Southerly winds
will increase as well, but the strongest winds will hold off
until tonight and Sunday.
Warm air advection pattern could result in high temperatures occurring late in
the day or even right before midnight as some location.
Short term /6 PM this evening through Sunday night/...
neutral upper trough becomes negatively tilted by Sunday morning
with a vigorous shortwave moving through New England. At the
sfc, low pres in the Ohio Valley this evening will strengthen as
it tracks through the eastern Great Lakes and into southeast Canada
through Sun night. 00z ec has trended a little deeper with the
low but not as deep as the GFS/CMC. The NAM is weaker.
Warm front should lift through this eve with increasing S winds
in the low levels. Cold front then approaches from the west with
S-SW winds increasing further and a band of moderate to heavy
showers sweeping across with the front overnight.
Confidence in any wind-related hazards remains higher across eastern
CT and Long Island, where a Wind Advisory has been issued for
tonight into Sunday. Given a significant low-level mass
response to the potent upper system, the potential still exists
for strong gusts tonight as a jet (50-60kt at 925 mb)
strengthens across the coast. Naefs suggest low-level jet speeds
significantly stronger than normal for this time of year - in
the 90-98th percentile from 850-700 mb. As previous discussions
have mentioned, questions still remain on how much of these
winds will be able to mix to the surface. However, given the
antecedent dry air mass, saturation may be somewhat slow, and is
supported by sref probabilities showing only a 25% chance of
ceilings below 3000 ft by 06z/sun. Mixing to 3000 ft would
certainly allow gusts perhaps in the range of 50-55kt across
eastern Long Island and eastern/coastal Connecticut, especially
after the passage of the warm front. There will be another
chance to mix stronger winds to the surface with the arrival of
any showers/convection as the cold front pushes through the
There is also very limited elevated instability across the east
end of Li so have added in the possibility for a rumble of
thunder for a few hours early Sun morning. Otherwise, rain ends
from west to east by late morning/early aftn with clearing skies.
Could end up with some broken clouds from lake effect streamers
well north/west of the city, but no pcpn is expected to make it into
the County Warning Area. There is some uncertainty with the timing of the cold
air working in behind the front, but expect falling temperatures
during the aftn.
Winds may briefly abate Sunday morning following the frontal
passage, before strengthening again into the afternoon from the
west-northwest with the passage of a strong mid- level vorticity maximum.
Confidence in any Wind- Advisory level sustained speeds/gusts
remains highest across eastern CT/Long Island closer to the
departing low. Otherwise, areas farther west will need to be
monitored for possible inclusion in the Wind Advisory for
Gradient remains tight Sun night with cold air advection continuing, thus gusty
Long term /Monday 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 European model (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 European model (ecmwf) is much
different than the GFS, which pours the cold air into the
region. The European model (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
The GFS does spin up a low along the subtropical jet and tracks
it east of the area on Friday. The European model (ecmwf) spins up something
similar on Saturday. This feature will need to be watched for
any westward trend.
Aviation /09z Saturday through Wednesday/...
high pressure slides east of the region today, with a low pressure
system approaching from the west.
VFR through this morning, with increasing potential for rain showers
and MVFR or lower conds developing late today into tonight.
Southerly winds increase this morning into this afternoon. SW winds
15 to 20 kt with gusts 25 to 30 kt likely for coastal terminals
late today into this evening.
Outlook for 06z Sunday through Wednesday...
late Saturday night...MVFR or lower conditions in -shra. Low level wind shear
possible for eastern terminals at night due to SW flow 40-50 kt at 2
kft above ground level. S-SW winds g25-35kt and occasionally higher for coastal
terminals. Low prob for a band of +shra and isolated thunder.
Sunday...conditions gradually improve to VFR with showers ending by
afternoon. Strong northwest windshift Sunday morning, with northwest winds g30-
40kt through the day. Gusts diminish to 25-30 kt Sunday evening.
Monday...VFR. West-northwest winds g20-30kt. Gusts diminish gradually at
Tuesday...mainly VFR. MVFR possible late Tuesday night with
showers. SW winds g15-20kt.
Wednesday...MVFR possible with showers. West-northwest winds g15-20kt.
tranquil conditions on the seas will be short-lived this
morning prior to strengthening southwesterly winds ahead of a cold
front. Gale-force winds initially on the ocean waters by afternoon
will spread to all other waters as the front nears, with seas
building in response. Overnight, a low level jet is expected to
strengthen along the coast, with the possibility of storm-force
gusts reaching the surface, mainly east of Fire Island on the ocean
waters. A storm watch remains in effect.
The front passes from west to east tomorrow morning, with a brief
lull in winds before they strengthen again from the west-northwest. Gale-force
winds will continue into Sunday night, before gradually weakening to
sca-levels. Small Craft Advisory conditions may continue into Tuesday before
gradually weakening into Wednesday and Thursday as high pressure
builds across the area.
a band of moderate to locally heavy showers with a strong cold
frontal passage late tonight into Sunday morning should cause
no more than local nuisance impacts. Total rainfall is expected
to range between 1/2 to 1 inch.
water levels will approach minor flood thresholds with this
mornings 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/west flow would be felt mainly across eastern portions of
the Great South Bay into Moriches Bay. Elsewhere any impacts
would be brief and localized.
CT...Wind Advisory from 10 PM this evening to 6 PM EST Sunday for
New York...Wind Advisory from 10 PM this evening to 6 PM EST Sunday for
Marine...Gale Warning from 6 PM this evening to 6 am EST Monday for
Storm watch from this evening through Sunday morning for
Gale Warning from 1 PM this afternoon to 6 PM EST this evening
Gale Warning from 1 PM this afternoon to 6 am EST Monday for