Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
458 am EDT Tuesday Jul 28 2015
high pressure over the Ohio Valley builds east and into the area
through middle week. A cold front approaches from the west Wednesday
night and Thursday morning...then slowly crosses the tri-state
through Thursday night. High pressure then builds in from the west
into the weekend. The Bermuda high ridges in from the west early
Near term /until 6 PM this evening/...
a weak short wave trough will move across New England this morning
sending a weak cold front/trough to the north of the area. This
boundary dissipates with a thermal trough setting up near or just
west of the NYC metropolitan this after. At the same time...a high
amplitude ridge over the middle MS valley extending north into south
central Canada builds east toward the eastern Seaboard through
middle week. The combination of the warming aloft and S/SW flow at
the surface will result in very warm to hot and muggy conditions
across the tri-state area. With the lack of a surface trigger...and
a developing subsidence inversion...convection is unlikely.
There will be some instability clouds across the area due to
daytime heating...but mainly looking at mostly sunny skies with
highs in the lower 90s inland and across portions of the NYC
metropolitan...but a bit cooler across Li/CT. Due to the combination of
the high heat and humidity...heat indices will in the lower to
middle 90s for most locations. Per local criteria...a heat advisory
will be issued for NYC for heat index values in the middle and upper
90s today and tomorrow.
There is a moderate risk for rip currents at the ocean beaches
Short term /6 PM this evening through 6 PM Wednesday/...
conditions continue to warm with ridging building in both aloft
and at the surface. A thermal trough will redevelop on Wednesday which will
keep the area in S/SW flow...with a continuation of high dew point
air across the region. Highs on Wednesday look to be a couple of
degrees warmer than Tuesday with heat indices in the middle and upper
90s for most locations. Once again...a lowering subsidence
inversion and lack of a trigger will keep a lid on any convection.
The overnight period will be very muggy with lows close to dew
points around 70.
Long term /Wednesday night through Monday/...
the axis of a northern stream deep layered ridge builds over the
area Wednesday night...with associated subsidence keeping things dry
and relatively cloud free. It appears the southern part of the ridge
maybe undercut by a 700-500 hpa shortwave late Wednesday night. This
should allow for just enough mixing for temperatures to fall a few
degrees lower than previously forecast. Lows Wednesday night are
based on a blend of NAM 2-meter temperatures with a mixture of
ecs/met/mav guidance. Values should be 5-10 degrees above normal.
There could be some mainly isolated showers/thunderstorms to the northwest
of NYC Thursday morning as a pre-frontal trough develops. Most of
the precipitation though is associated with a northern stream trough
that will pass to the north Thursday night...along with its associated
surface cold front. As a result the bulk of any showers and
thunderstorms should occur Thursday afternoon mainly to the northwest of
NYC and over the remainder of the County Warning Area Thursday night. The 00z
GFS/ECMWF/CMC all have no precipitation from 12z Friday on and a
reasonable interpretation has things dry by 12z Friday...so bring all
precipitation to an end Thursday night from northwest to southeast as the front
Model BUFKIT soundings still showing a small cap around 650
hpa...but much weaker than the past couple of days. Most models also
tend to limit any significant cape to over NE New Jersey/lower Hudson
Valley/SW CT and maybe NYC Thursday afternoon. So the two limit the
risk of any stronger to possibly severe storms to this area. With 30
knots of bulk shear could see a mixture of pulse storms and some bowing
segments. Given the potential for organized convection...and 1000-
1500 j/kg of cape...Storm Prediction Center has placed NE New Jersey/lower Hudson Valley/SW CT
and NYC under a marginal risk for severe thunderstorms. Will
highlight this threat in the severe weather potential statement.
A blend of mav/met/ecs guidance...NAM 2-meter temperatures and a mix
down from 975-875 hpa was used for highs on Thursday. This is less
mixing than previously forecast...so temperatures on Thursday are
now forecast to be several degrees cooler...mainly in the middle-upper
80s. However a few 90 degree readings in urban NE New Jersey cannot be ruled
out. Heat indices as a result are now forecast to be below 95
degrees County Warning Area-wide on Thursday.
Lows Thursday night are based on a blend of NAM 2-meter temperatures
with a mixture of mex/men/ekd/ece/ecm/wpc guidance. Values should be
around 5 degrees above normal.
For now have gone with a dry forecast Friday-Saturday...with the
region on the southern edge of a northern stream trough setting up
to the north. As a result...most if not all associated forcing should
stay to the north of the area. Another complication is the cold front is
forecast to stall out off the Middle Atlantic States into the weekend.
There is some variety in exactly how far to the S the front
stalls...with solutions creeping north over the past few days. If
this trend continues...might need to revisit probability of precipitation over S zones.
The models then begin to differ with how far S/how long the trough
digs into the NE U.S. With the GFS sharper with the trough...digging
it in into Monday. The European model (ecmwf) however...keeps the bulk of the trough
to the north and in fact builds in a westward extension of the sub-
tropical ridge by early next week. Noting that we are currently in a
fairly climatological pattern right now...have favored the more
climatological solution of the European model (ecmwf) right now Saturday night-
Monday. So anticipate hot and humid conditions early next week.
However...do have slight chance probability of precipitation in for now Monday in case the
GFS ends up being more correct.
Temperatures Friday-Monday...a blend of mex/men/ekd/ece/ecm/wpc
guidance was used with above normal temperatures forecast.
However...given the large differences in patterns forecast by the
GFS and European model (ecmwf)...there is quite a bit of uncertainty in temperatures
for the weekend and early next week.
Aviation /09z Tuesday through Saturday/...
high pressure builds through the taf period with VFR prevailing
much of the time. A few outlying terminals will have some patchy
MVFR or lower fog/ceilings into daybreak. Also...there will be some
possible MVFR haze along the coast. The probability is too low at
the moment to include MVFR haze in taf.
Light onshore winds less than 10 knots much of the taf period. For
this afternoon...city terminals will reach 10-13 knots with sea
..NY 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: no unscheduled amendments expected.
Klga fcster comments: sound breeze duration may vary 1-2 hours
Kewr fcster comments: sea breeze arrival could vary 1-2 hours from
The afternoon kewr haze potential forecast is green...which
implies slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: sea breeze arrival could vary 1-2 hours from
Khpn fcster comments: low confidence on the MVFR fog before 11z.
Kisp fcster comments: low confidence on the MVFR fog before 11z.
Outlook for 09z Wednesday through Saturday...
Wednesday-Thursday...mainly VFR. 5-6sm haze development
possible. SW winds with afternoon seabreeze development at coastal
terminals. Thunderstorms and rain possible Thursday aftn/eve.
Friday and Saturday...VFR.
a weak pressure gradient across the forecast waters today into
tonight will keep winds and seas below small craft levels.
Gradient wind from the south strengthens Wednesday with the possible
development of a coastal jet. Still though...gusts should remain
below 25 knots...strongest west of Fire Island Inlet.
Even factoring in the seabreeze and the passage of a cold front
late Thursday...winds should be 15 knots or less on the waters
Wednesday night-Saturday. At this time...there is no reliable
prediction of any significant swell moving into the coastal ocean
waters in this time frame...so seas should remain below Small Craft Advisory levels
Wednesday night-Saturday consistent with the forecast winds.
dry conditions are forecast through middle week.
While widespread significant rainfall is not expected with any
showers/thunderstorms Thursday/Thursday night...there is the
potential for locally heavy rainfall with any stronger convection.
If this were to occur...than localized minor urban/poor drainage
flooding would be possible.
It should then be dry from Friday into the weekend.
record highs for Wednesday July 29 2015...
Location..........record high/year.........Forecast high
j f Kennedy................99/2002.................89
New York...heat advisory from noon today to 6 PM EDT Wednesday for