Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
617 am EST Wednesday Nov 25 2015
high pressure over the region moves off the New England coast
today. The high drifts east tonight through Thursday. High
pressure retreats to the northeast Thursday night. A cold front
approaches from the west Friday...then slowly crosses the tri-
state Friday night and Saturday. The front then stalls out to the
south through the weekend...as high pressure builds in to the
north. The high then slowly retreats to the northeast early next
week. A complex storm system will approach from the west Tuesday.
Near term /until 6 PM this evening/...
clear conditions with light wind continue with high pressure over
the area. Made some minor adjustments to temperatures and dew
points for early this morning as temperatures along the coast did
not fall off as low as expected.
An upper ridge moves across the region today with the axis
shifting to the east around 00z Thursday. At the surface high
pressure will build to the northern New England coast. As a result
strong subsidence and little moisture will keep the region mostly
cloud free. There may be some high clouds across the western
portions of the region by late in the day as the ridge moves east.
Warm advection through the day and maximum heating...temperatures
will rise to seasonal levels.
Short term /6 PM this evening through 6 PM Thursday/...
warm advection continues tonight into Thursday...gradually weakening
by Thursday morning. Tonight into Thursday and deep southwest flow
develops as the ridge moves east as does the surface high. A
southeast to south flow develops tonight and continues into
Thursday. With the onshore flow and a developing surface inversion
tonight into Thursday low clouds will be trapped under the
inversion. Expect clouds to develop late tonight into Thursday
morning as the inversion steepens. Then clouds remain through
Thursday. Increasing low level lift will allow for some light
drizzle to develop by Thursday afternoon. Lowered probability of precipitation to slight
chance with the weak forcing in the area and the lowest levels are
not completely saturated.
Temperatures tonight will fall off quickly this evening...then hold
steady or possibly rise a degree of so as the warm advection
remains and clouds move into the area.
Long term /Thursday night through Tuesday/...
SW flow aloft Thursday night...with onshore flow in the immediate
low levels. This is a typical set up for low clouds/drizzle...with
moisture trapped under an inversion from around 1000-975 hpa. So
have a slight chance of drizzle (pops reflect probability of
measurable drizzle vice express a chance of occurrence of drizzle -
which is likely).
Flow becomes more west-southwest during the day on Friday in the low
levels...this should bring an end to the drizzle...and allow for
breaks in the low clouds by afternoon...if not sooner.
For lows Thursday night...a blend of mav/met/ecs guidance and NAM 2-
meter temperatures was used...with values around 10-15 degrees above
normal. For highs on Friday...a blend of met/mav guidance...NAM 2-
meter temperatures and a mix down from 975 hpa per BUFKIT soundings
was used. Highs should be around 10 degrees above normal.
Models differ with timing of system for Friday night-Saturday...and
then how far to S its surface frontal reflection stalls out through
the weekend. This is mainly due to differences in handling of ridging
centered over the southeastern U.S. - With the European model (ecmwf)/NAM extending
the ridging farther NE of the middle Atlantic coast than the CMC and to
a lesser extent the GFS...and a trough/possible closed low over/just
east of the Bahamas. As a result the European model (ecmwf)/NAM are the slowest in
bringing the surface front through...the CMC the fastest...and the
GFS in between. Noting the European model (ecmwf) in general handles ridging along
the East Coast better than most models in this time frame...have
leaned towards slower European model (ecmwf) solution Friday night-Saturday. So have
chance probability of precipitation mainly northwest 1/4 of the County Warning Area Friday night with chance probability of precipitation
It should be noted that outside of the European model (ecmwf)...there is some
suggestion the precipitation falls apart as the front passes on
Saturday in response to the shearing out of the supporting shortwave
aloft. Not quite ready to go to only slight chance probability of precipitation or a dry
forecast for Saturday...but cannot rule out needing to ultimately
move the forecast in that direction.
Zonal flow Saturday night/Sunday...gives way to northwest flow aloft Sunday
night as a northern stream trough sharpens over the Canadian
Maritimes. With no shortwaves currently forecast to be embedded in
the flow - have gone with a dry forecast Saturday night...then
slight chance probability of precipitation over only the SW 1/3 of the County Warning Area Sunday/Sunday
night in response to a passing southern stream shortwave.
Deep layered ridging builds in Monday...with its axis beginning to
slide to the east Monday night. Associated high pressure should keep
a stalled front far enough to the S that the area should remain dry.
However...this is a change from previous runs...so do have slight
chance probability of precipitation Monday/Monday night to more gradually trend this
change...instead of going straight to a dry forecast.
The axis of the deep layered ridge should finish sliding to the east
on Tuesday...with over running flow setting up behind it. Have
chance probability of precipitation all day on Tuesday. However...exact timing will
ultimately be determined by how fast the ridge axis slides to the
east - this could change the onset time of precipitation by 12-24
hours from current expectations. However...with chance probability of precipitation in the
forecast all day...if there is any precipitation in the morning...it
could be in the form of snow and rain across S CT/the lower Hudson
Valley and interior NE New Jersey...changing to all rain by afternoon. Only
rain is currently expected over NYC/Long Island/east NE New Jersey.
Temperatures Friday night-Tuesday were based on a blend of
mex/men/ekd/ece/ecm guidance...with wpc guidance mixed in from
Saturday on...and NAM 2-meter temperatures added in Friday night.
For now looking at above normal lows Friday night...then near normal
temperatures on Saturday (depending on the exact timing of the
surface cold front). Temperatures then run from slightly below to
slightly above normal Saturday night-Tuesday.
Aviation /12z Wednesday through Sunday/...
strong high pressure slowly retreats to the NE through tonight.
VFR through 00z. Light north winds this morning becoming southeast in the
afternoon under 10kt. MVFR ceilings move in east to west tonight...likely holding
off until after 12z at NYC terminals.
... Metropolitan enhanced aviation weather support...
Detailed information...including hourly taf wind component forecasts can
be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)
Kjfk fcster comments: wind shift S of 130 degrees magnetic could be
+/- 1-2 hours.
Klga fcster comments: wind shift S of 130 degrees magnetic could be
+/- 1-2 hours.
Kewr fcster comments: wind shift S of 130 degrees magnetic could be
+/- 1-2 hours.
The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: no unscheduled amendments expected.
Khpn fcster comments: no unscheduled amendments expected.
Kisp fcster comments: no unscheduled amendments expected.
Outlook for 12z Thursday through Sunday...
Thursday-Thursday night...mainly MVFR.
Fri-Sat...mostly VFR. MVFR possible in -shra Friday night into Sat.
Chance north-NE gusts 20-25kt Sat morning.
Sunday...chance of sub-VFR in rain late.
seas on the ocean waters running about a half foot below forecast
through 12z. Otherwise the forecast of wind and seas on track.
With high pressure centered over northern New England this
morning...and moving east through Thursday...a weak pressure
gradient force will exist across the forecast waters. As a result
both wind and seas will remain below Small Craft Advisory levels.
A relatively relaxed pressure gradient will be over the
waters for most of the time from Thursday night-Sunday...so winds
will mainly be 10 knots or less in this time frame.
The exceptions Thursday evening over the coastal ocean waters east
of Moriches Inlet...where winds should diminish from around 15
knots...and on Saturday on the coastal ocean waters where winds of
around 15 knots are possible with a frontal passage.
Thus...sub-Small Craft Advisory conditions are expected on the non-
ocean zones Thursday night-Sunday.
Seas of around 5 feet are possible on the coastal ocean waters are
possible Friday-Saturday. As a result...a Small Craft Advisory for
hazardous seas maybe needed for these waters during this time...if
these seas are realized (which is uncertain at this time).
dry today. There is a slight chance of drizzle Thursday.
Less than 1/4 inch of precipitation is expected Thursday through
Saturday...then it should be mainly dry from Saturday night into
early next week.