Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New York New York
1046 PM EDT Tue Oct 25 2016

high pressure slowly builds in from eastern Canada through
Wednesday then moves east Wednesday night. High pressure then
builds in to the southwest from Friday and Friday night. A frontal
boundary then stalls nearby from Saturday into Monday, with waves
of low pressure riding along it. High pressure then builds across
the region through Tuesday.


Near term /until 6 am Wednesday morning/...
upper trough lifts out of New England/eastern Canada overnight.
At the surface, polar high pressure builds southeast from eastern
Canada with gusty northwest winds gradually diminishing.

The coldest airmass thus far this fall will continue to filter
into the region with the interior dropping to around freezing, and
coastal locations into the mid and upper 30s by daybreak. The
Pine Barrens region of eastern Li could also see some below
freezing temperatures if winds decouple. These readings are
nearly 10 degrees below normal. A freeze warning remains up across
the interior.


Short term /6 am Wednesday morning through Wednesday night/...
high pressure builds in briefly both aloft and at the surface with
another day of gusty northwest winds to start. Gusts will mainly be
confined to the first half of the day and only up to 20 mph.
Conditions will remain unseasonably cold with readings struggling
to get to 50. Stayed just below met/mav MOS based on upstream

Models have trended slower with the southern branch Pacific
storm system approaching from the Great Lakes Wednesday night.
Clear skies and diminishing winds will allow for strong
radiational cooling with many locations inland dropping to below
freezing. Should a freeze not occur Wednesday morning to end the
growing season, another freeze warning will likely be needed for
portions of the forecast area. Mid and high level clouds increase
overnight with gradually rising temperatures. Any precipitation is
forecast to be just west of the lower Hudson Valley/NE New Jersey by
daybreak Thursday.


Long term /Thursday through Tuesday/...
northern stream ridging exits to the east on Thursday as a
northern stream closed low moves across the eastern Great Lakes.

How fast precipitation develops on Thursday will in large part
be determined by how quickly the northern stream ridging exits
and exactly how dry the low levels are Thursday morning.

The European model (ecmwf) remains the most aggressive in bringing in
precipitation. Looking at isentropic lift and saturation on the
I-285 to I 300 surfaces on the European model (ecmwf) note flow is almost parallel
to pressure contours over the County Warning Area at 12z Thursday - so appears
European model (ecmwf) is likely to fast in bringing in precipitation (it had this
bias last winter also). As a result, limit slight chance pops at
12z Thursday to basically the northwest 1/2 of Orange County - then
gradually increase pops to categorical throughout by 21z

The question is how fast do the low levels warm north/west of NYC
before the precipitation begins. High resolution models like the
NAM typically handle low level cold air better than the GFS
or ensembles, so weighed temperature forecast towards NAM
2-meter temperature and wet-bulb temperature once precipitation
is forecast to have started.

For now, it appears that if there is any precipitation over
the lower Hudson Valley and northern portions of NE New Jersey Thursday
morning, a wintry mix of snow/sleet/rain/freezing rain is
possible depending on elevation and timing. If confidence in
occurrence of freezing rain occurs, would need to consider a
winter weather and/or Freezing Rain Advisory over at least
portions of the lower Hudson Valley for early Thursday morning.
Any snow/sleet accumulation will be less than 1 inch, if any at

Regardless all areas should be to plain rain by early
Thursday afternoon, if not sooner. Isentropic lift increases
significantly by afternoon, so have gone with moderate rain in
the grids, though would not be surprised if locally heavy.

The closed northern stream low tracks to the north Thursday night
with its associated secondary surface low tracking near Long
Island late Thursday night then to around Cape Cod by 12z Friday.
Based on this have categorical pops for moderate rain Thursday
evening, tapering off from W to E, with dry conditions expected
over all but far NE New London County by 12z Friday. Showalter
indices fall to the 0 to 1c range from around 2-8z from west to east so
have a slight chance of thunder in the forecast as well Thursday
night. Refer to the hydrology section of the afd for details on
rainfall amounts and any potential impacts.

Highs on Thursday were based on a blend of ecs/met/mav guidance,
NAM 2-meter temperatures and a mix down from 950-875 hpa per
BUFKIT soundings. Wet-bulbing will serve as the limiting factor
on high temperatures - with higher elevations well north/west of NYC
struggling to reach the lower-mid 40s and the remainder of the
area mainly in the upper 40s to lower 50s. Note if the developing
secondary low tracks farther S than currently forecast and the
low level flow remains more northerly - then highs might need to
be undercut by 5-10 degrees depending on exact track of low and

Lows Thursday night were based on a blend of mav/met/ecs
guidance and NAM 2-meter temperatures and should run around
normal in the immediate NYC Metro and around 5 degrees above
normal elsewhere.

A relatively flat deep layered ridge builds in Friday-
Saturday night, then slides to the east Sunday. Associated
subsidence should keep things dry Friday-Friday night. A backdoor
cold front pushes down from the north Saturday, and stalls out
near by, but likely to the north through Sunday. Depending on
exactly where the front stalls there could be a period of rain
over the weekend. For now have kept pops to slight chance to low
end chance - but this does not mean it will rain for all of/most
of the weekend. On the whole there is a better chance for the
weekend to remain dry than be wet, especially over NYC/Long
Island/southern portions of NE New Jersey.

A northern stream trough passes to the north Sunday night - with
some question as to how far north it GOES. The GFS keeps things dry
while the European model (ecmwf)/CMC bring some rain to the region kept chance to
slight chance pops in for Sunday night as result.

With the GFS and European model (ecmwf) both showing deep layered ridging building
in Monday/Monday night and sliding offshore Tuesday - went with a
dry forecast at this time.

For temperatures Friday-tuesday:
a blend of mav/met guidance, NAM 2-meter temperatures and a mix
down from 875 hpa was used for highs on Friday, with values
forecast to be around 5-10 degrees below normal. Lows Friday
night were based on a blend of mex/men/ece/ecm/ekd/wpc guidance
and should be near normal. The superblend was used for
temperatures Saturday-Tuesday, with near normal temperatures on
Saturday then above normal temperatures Sunday, below normal
temperatures Monday, and above normal temperatures on Tuesday.


Aviation /00z Wednesday through Sunday/...
high pressure slowly builds into the region through Wednesday.

VFR through the taf period.

Winds around 310 true shift slightly towards 330 true overnight
and Wednesday. Gusts for the city terminals have generally ended
with the exception of kjfk, which could continue until 05z-06z.
Klga and kewr may see an occasional gust to 20kt through 05z. The
magnitude of the winds will be decreased on Wednesday.

... Metro enhanced aviation weather support...

Detailed information...including hourly taf wind component fcsts can
be found at: http:/www.Weather.Gov/zny/n90

Kjfk taf comments: gusts may end or become more occasional an hour
or 2 before 06z.

Klga taf comments: an occasional gust to 20kt is possible through

Kewr taf comments: an occasional gust to 20kt is possible through

Kteb taf comments: no unscheduled amendments expected.

Khpn taf comments: an occasional gust to 20kt is possible through

Kisp taf comments: no unscheduled amendments expected.

Outlook for 00z Wednesday through Sunday...
Wednesday night...VFR with decreasing northwesterly winds.
Thursday...MVFR or lower possible in rain. Potential for a wintry
mix across the interior before 15z. Southerly winds.
Friday...VFR with strong northwest flow behind a cold front.
Gusts to at least 25 kt are expected at this time.
Saturday and Sunday...VFR with southwest flow possible.


Small Craft Advisory conditions will linger on the ocean waters overnight and into
for the ocean waters. For Wednesday into Wednesday night, high
pressure builds into the waters with sub-Small Craft Advisory conditions.

Small Craft Advisory conditions are likely on the coastal
ocean waters and possible on the non-ocean waters from Thursday
into Friday night. The pressure gradient relaxes sufficiently by
the weekend to limit winds to 15 kt or less on Saturday and to 10
kt or less on Sunday.


dry weather remains forecast through Wednesday night.

From around 0.75 to 1.25 inches of rain is forecast Thursday and
Thursday night, with locally higher amounts possible. The ponding
of water in typical poor drainage areas cannot be ruled out as a


Okx watches/warnings/advisories...
CT...freeze warning from 2 am to 9 am EDT Wednesday for ctz005>008.
New York...freeze warning from 2 am to 9 am EDT Wednesday for nyz068>070.
New Jersey...freeze warning from 2 am to 9 am EDT Wednesday for njz002-004-
Marine...Small Craft Advisory until 8 PM EDT this evening for anz330-
Small Craft Advisory until 6 am EDT Wednesday for anz350-353-


near term...dw
short term...dw
long term...maloit

National Weather Service Glossary of Abbreviations