Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
546 am EDT Wednesday Jul 29 2015
high pressure builds off the middle Atlantic coast today. A cold
front approaches from the west tonight and Thursday morning...then
crosses the tri-state Thursday afternoon and night. Weak high
pressure builds in Friday through Saturday. A cold front
approaches Saturday night...weakening and dissipating with its
arrival on Sunday. Weak high pressure follows for Sunday with
another weakening cold front approaching Sunday night. This too
dissipates within the region early next week with main high
pressure staying in the western Atlantic and the main low pressure
staying in southeast Canada.
Near term /through tonight/...
a deep layered northern stream ridge continues to build over the
County Warning Area today...with the ridge axis passing over the area tonight.
Subsidence under the ridge will keep things dry through
tonight. Cloud cover will also be at a minimum...other than maybe
some afternoon cumulus...until some high clouds begin to build in
from SW to NE late tonight as the ridge axis moves to the east.
Main story today will be the heat...with highs mainly from around
90 to the middle 90s...except middle to upper 80s on the Twin Forks of
Long Island and coastal southeast CT. These temperatures combined with
dewpoints from the middle 60s to around 70 this afternoon will
produce heat indices in the 90s...with middle-upper 90s across the
NYC metropolitan and urban portions of S CT. Based on this being the
second consecutive day with heat indices of 95-99 in NYC...have
continued the heat advisory there.
Lows tonight are based on a blend of mav/ecs/met guidance with NAM
2-meter temperatures. Readings should be between 5-10 degrees
There is a moderate risk for the meteorological enhancement of
rip current formation at Atlantic beaches into this evening.
Short term /Thursday through Thursday night/...
the deep layered northern stream ridge exits to the east Thursday
morning...with a northern stream trough moving in behind it
through Thursday night. Precipitation will generally run ahead of
the trough...and not to far ahead of its associated surface cold
front. Confidence in the occurrence of precipitation has lead to
an increase of probability of precipitation to likely Thursday afternoon and evening.
Along with this...have also put a mention of locally heavy
rainfall in the forecast. Refer to the hydrology section of the
afd for details on amounts and any potential impacts.
However...with BUFKIT soundings still showing some warming in the
layer from around 650-550 hpa...have kept the probability of
thunder to chance. Models are fairly consistent in the timing of
the end of precipitation...and so expect it to come to an end from
northwest to southeast Thursday night as the surface cold front exits to the
Generally have 1500-2000 j/kg of surface based cape forecast over
all of the County Warning Area but the Twin Forks and the immediate coast of southeast
CT. With a bulk shear of around 30 knots...favor a combination of
pulse storms and some multi-cellular clusters and/or bowing
segments. With the region forecast to be in the right rear
quadrant of an around 80 knots 250 hpa jet...and the passing of a
25-30 knots 950-850 jet near/over the area Thursday
afternoon/evening...there is sufficient forcing to go along with
the cape and shear for strong to possibly severe storms.
Accordingly Storm Prediction Center has expanded the marginal risk of severe
thunderstorms to encompass all but basically southern Suffolk
County. Will make a minor adjustment to this for the severe weather potential statement...and
highlight the severe threat for all but eastern Suffolk
County...noting the lower convective available potential energy there.
For highs on Thursday used a blend of mav/met/ecs guidance with
NAM 2-meter temperatures and a mix down from 975-825 hpa per
BUFKIT soundings. Highs should be around 5 degrees cooler than
today...as the core of the warm air aloft moves to the east with
the ridge axis. Forecast dewpoints however have increased from
previous forecasts and now are around 70-lower 70s. As a result
expect heat indices mainly in the lower 90s...with some middle 90s in
NYC/urban NE New Jersey and the I-91 Corridor North of New Haven. Only have a
few gridpoints of heat indices of 95 in NYC proper...but given
uncertainties with dewpoints...and that a change in 1 degree in
temperature and/or dewpoint makes a bit of difference in heat
index...do not have the confidence to cancel the heat advisory for
NYC for Thursday.
For lows Thursday night...a blend of mav/met/ecs guidance and NAM
2-meter temperatures was used...with values forecast to be around
5 degrees above normal.
Long term /Friday through Tuesday/...
overall Friday into next week...no significant large scale changes
within the region in the middle to upper levels. The main upper level
jet stays mostly northeast of the region with the 250mb height
gradient gradually decreasing going into next week. The 500mb height
is forecast to generally stay between 5770m to 5830m much of the
period. The lowest heights will be marked by the the passage of
shortwaves within a longwave trough over the northeast. These are
shown to occur Saturday night into early Sunday as well as Monday
night into Tuesday. The local region will be at the base of this
longwave trough. Much of the positive vorticity advection will be
located north of the region...leaving a void in synoptic forcing
over the local area.
The middle levels will likewise exhibit similar trends at the surface
with overall a weak pressure gradient remaining. The cold fronts
approach Saturday night into early Sunday and early next week with
weak high pressure for other time periods within the long term. The
fronts dissipate without much change of airmass for the region.
Therefore...the probability of precipitation for showers and thunderstorms will in the
slight chance range due to timing at night with less instability and
the aforementioned lack of synoptic forcing for this Saturday night.
The probability of precipitation are also slight chance for early next week due to larger
uncertainty but with some more instability to work with potentially
for any convection during the day.
The airmass will continue to be very warm and humid. Much of the
area has forecast highs of middle 80s to near 90 with forecast lows middle
60s to lower 70s. The dewpoints are forecast to stay well within the
60s much of the time period.
Aviation /09z Wednesday through Sunday/...
a weak low pressure trough will remain over the area...while high
pressure remains to the west.
Generally VFR this morning...although a few terminals outside NYC
metropolitan could observe patchy MVFR fog. Kgon could go IFR or lower
as was the case last night. Expect any MVFR or lower conditions to
quickly improve to VFR by 13z-14z.
Light and variable winds this morning will increase to 5-10 knots by
late morning/early afternoon from the SW. Speeds increase to at
least 10 knots for coastal airports during the afternoon.
..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: wind direction may vary from 160-180 in the
Klga fcster comments: timing of onset of south winds may vary by
1-2 hours...and direction may vary from 160-180.
Kewr fcster comments: wind direction may vary from 180-210 in the
The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: wind direction may vary from 180-210 in the
Khpn fcster comments: wind direction may vary from 170-200 in the
Kisp fcster comments: no unscheduled amendments expected.
Outlook for 06z Thursday through Sunday...
Wednesday night...MVFR visibility possible late.
Thursday...early morning haze with MVFR conditions...then scattered
afternoon/evening thunderstorms with MVFR or lower conditions.
a weak to moderate strength pressure gradient will generally keep
winds at 15 knots or less through Thursday night. However...could
see a combination of the tightening of the pressure gradient
ahead of a cold front and the seabreeze bring winds to 20 knots in
the New York bight region Thursday afternoon/evening. For now it appears
though that any gusts to 25 knots in this region will be occasional
at most. Given this...and current expectation of no significant
swell through Thursday night...expect seas to remain below 5 feet
through Thursday night also.
Sub Small Craft Advisory conditions are forecast on Friday and Friday night with weak
high pressure moving across. The below Small Craft Advisory conditions are forecast
to continue into much of Saturday until some higher seas from
continued southerly fetch will move in late Saturday afternoon
through Sunday. Ocean seas are forecast to reach 5 to 7 feet with this
fetch...so Small Craft Advisory potential will be there.
dry through tonight.
Around 1/4-1/2 inch of basin average rainfall is possible Thursday and
Thursday night. However...with precipitable waters forecast to
over 2 inches Thursday afternoon and evening...locally heavy
rainfall is possible with any stronger convection. If this
occurs...then minor urban/poor drainage flooding would be
No significant widespread rain expected Friday through Tuesday.
record highs for Wednesday July 29 2015...
Location..........record high/year.........Forecast high
New York...heat advisory until 8 PM EDT Thursday for nyz072>075-176-178.