Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1033 PM EDT Tuesday Jul 22 2014
high pressure will continue to move offshore as a cold front
approaches from the west. The front will move across from
Wednesday night into Thursday...followed by building high pressure
on Friday. The high will weaken on Saturday...then low pressure
passing to the southeast will impact the area Sunday into Monday.
An associated cold front will approach late day Monday...and move
across Monday night into Tuesday.
Near term /until 6 am Wednesday morning/...
dry conditions expected overnight with weak shortwave energy
sliding south of the region.
Warm and humid night on tap with lows in the 60s to low 70s. The
warmest temperatures will occur in/around NYC due to the urban heat
island effect. Surface dew points will climb through the middle 60s and
into the upper 60s. Can expect patchy fog to develop away from the
Short term /6 am Wednesday morning through Wednesday night/...
hot and increasingly humid air mass remains over the area
Wednesday. With high pressure departing and cold front approaching
from the west...SW flow increases throughout the day...and surface
dewpoints will rise through the 60s and into the lower 70s. Maximum
temperatures on Wednesday will top off in the lower 90s across NYC and NE
New Jersey...and will be in the upper 80s to near 90 elsewhere. Temperatures will
be sightly cooler near the south coasts. The heat index on
Wednesday will generally top off in the low to middle 90s...expect
for NYC/NE New Jersey...where the heat index will be in the middle to upper
90s. Since the heat index in NYC will not reach 95 for 2
consecutive days...and since the heat index will remain below 100
across the County Warning Area...will not issue a heat advisory.
As cold front approaches...showers and thunderstorms will develop
north and west of NYC in the afternoon along a pre-frontal trough.
Showers and thunderstorms spread east Wednesday evening and
Wednesday night...and the bulk of the activity should hold off
until Wednesday night as the cold front passes through the region.
With the heat and humidity...ml MUCAPE values will range from
1000-1500 j/kg during the day...and then will drop to around 400
j/kg at night with the loss of the heating. 0-6 km bulk shear will
be weak during the day...and then will rise to 25-35 knots after 00z
Thursday. Cannot rule out strong winds with any thunderstorms...
but primary threat will be heavy rain due to precipitable waters around 2".
Flash flooding of low lying and poor drainage areas is possible.
Will not issue a hazardous weather outlook as the threat will not
Showers and thunderstorms taper off from west to east Wednesday
night as the cold front works its way across the region.
There is a moderate risk of rip currents...mainly Wednesday
after/evening with enhanced sea breeze development.
Long term /Thursday through Tuesday/...
the surface cold front should be to the east Thursday morning...but with the
800 mb front still yet to move across...a middle level trough still well to
the west and potential for a weak surface wave along the front to slow
its progress even further...will have likely pop to start across southeast
CT and eastern Long Island and chance elsewhere...with chances gradually
ramping down during the afternoon and early evening. Conds look
mainly dry for later Thursday night and more so into Friday as high pressure
builds from the west.
The high should weaken on Sat as flow aloft becomes more zonal.
As low to middle level moisture return commences...with precipitation
efficiency increasing back to over 1 inch by late day...and as middle
level shortwaves approach in zonal flow...should start to see
increasing chances for showers/thunderstorms beginning late day Sat into
The flow aloft should undergo significant amplification early next
week as an upper ridge builds in the western states and a potent
shortwave trough diving out of central Canada merges with an upper
low over Quebec...carving out a deep longwave trough over the
eastern states. There will be good chances for showers/tstms...
especially Sunday night into Monday morning as an associated wave of
low pressure passes just off to the southeast...then late day Monday into Monday
night with the approach of a cold front from the west.
Could see some leftover showers/thunderstorms on Tuesday mainly in the morning
as the cold front moves to the east...then drier and slightly cooler
air arriving through the rest of Tuesday into Tuesday night.
Aviation /03z Wednesday through Sunday/...
high pressure moves east as a cold front approaches Wednesday.
Generally VFR through the taf period. Patchy fog could result in
MVFR visibilities outside of NYC terminals late tonight. Otherwise...VFR
with possible late day showers/thunderstorms from NYC west. Any storm could
produce sub VFR conditions briefly late in the day Wednesday.
South winds diminish and remain light overnight. Sea breezes are
expected again Wednesday...with speeds increasing during the
afternoon once again.
Outlook for 00z Thursday through sun...
Wednesday night-Thursday morning...slow moving cold frontal passage. MVFR or lower conditions
in scattered-numerous showers/tstms.
Sun...chance of showers or thunderstorms. Sub-VFR possible.
winds will gradually subside through 06z...with sub-Small Craft Advisory conds
expected overnight. Low probability of fog on the waters based on
forecast dewpoints near or slightly below water temperatures...so have
removed from forecast.
Winds will increase to 15-20 knots once again on the ocean waters
Wednesday afternoon and to 10-15 knots with 15-20 knots gusts on the
rest of the waters ahead of an approaching cold front. Convection
likely Wednesday night. Seas will average 2-4 feet on the ocean and
around 1 feet elsewhere.
Outside of thunderstorms Thursday and late day Sat have high confidence in
quiet conds Thursday through Sat...then forecast uncertainty creeps in
beginning on Sunday. Have forecast continued quiet conds...but if an
approaching wave of low pressure and/or frontal system are
stronger than forecast...hazardous ocean seas could develop if
corresponding S-SW flow is stronger than forecast.
there is the potential for around 1/2 inch of rainfall from late
Wednesday through Thursday with locally higher amounts possible.
Precipitable waters are forecast to be around 2 inches on
Wednesday night...so locally heavy rainfall is possible in any
stronger convection. Areas experiencing locally heavy rainfall
could experience at least minor flooding of urban/poor drainage
area...and possibly localized flash flooding. The confidence in
the latter is currently less than 30 percent so will not highlight
in the hazardous weather outlook.
Low pressure passing just off to the southeast Sunday night into Monday
morning...followed by a cold frontal passage later Monday...have some
potential to produce heavy rain...as precipitation efficiency increases
to over 1.5 inches. This will depend first on the low track...then
on potential for training of cells ahead of the cold front...as
well as other mesoscale/thermodynamic factors. Given these
uncertainties it is too early to outlook this in the severe weather potential statement.