Scientific Forecaster Discussion
fxus61 kokx 180528
Area forecast discussion
National Weather Service New York New York
1228 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 am this 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
Short term /6 am this morning through 6 PM 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 southeast 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 west-northwest 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 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 /06z 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.
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. West-northwest gales should
continue after the cold frontal passage into at least Sunday
afternoon, and possibly into Sunday night especially on the
Small Craft Advisory conds will follow into Mon, and are still possible mainly
on the ocean into Tue. Conditions may improve to below advy
criteria on Wed.
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.
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/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.
Marine...Gale Warning from 6 PM this evening to 6 PM EST Sunday 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 PM EST Sunday for