Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1024 am EDT Tuesday Jul 22 2014
as a high pressure system moves slowly east of the area today...a
cold front will approach from the west on Wednesday. The cold front
crosses the area from Wednesday night into Thursday
morning...followed by high pressure building to the south of Long
Island into Saturday. A storm system then impacts the area into
early next week.
Near term /until 6 PM this evening/...
forecast remains on track. With high pressure over the region...skies
will be sunny with temperatures a few degrees above normal...topping off
in the middle to upper 80s...possibly around 90 west of the Hudson
Atlantic Ocean and Long Island Sound sea breezes will develop by
noon. Wind speeds will be 10 knots or less.
Will also continue a low chance for probability of precipitation...30 percent or less...for
showers/thunderstorms this afternoon for areas northwest of NYC. Brief...heavy
downpours are possible.
There is a moderate risk of rip currents...mainly this afternoon
through evening with enhanced sea breeze development and long
period southeast swells.
Short term /6 PM this evening through 6 PM Wednesday/...
tonight...SW winds will continue transporting higher dew points
across the region making it feel uncomfortable.
Wednesday...Summer heat and humidity returns with day time high
temperatures reaching around 90 across NYC and urban northeast New Jersey and
with heat index values rising into the middle and upper 90s. No
extended heat wave is forecast as the next cold front approaches.
A warm moist unstable maritime tropical air mass will set the
stage for the development of more numerous showers and thunderstorms by
Wednesday afternoon mainly west and north of NYC. Increased probability of precipitation to
likely category by 6 PM.
Primary potential hazard is heavy rain which could cause isolated
flash flooding mainly of low lying poor drainage areas. Can not
rule out the potential for a strong to possibly severe thunderstorm with
damaging winds being the primary threat.
Because more widespread flash flooding or severe storms are not
forecast...a hazardous weather outlook will not be issued at this
time for these potential hazards.
Long term /Wednesday night through Monday/...
have the potential for significant convection Wednesday
night...with the passage of a surface cold front through a rather
warm and humid air mass. There are some indications that convective available potential energy of
1000-1500 j/kg could persist at least through Wednesday
evening...and showalter indices of 0 to -2 persist through the
night...especially over eastern portions. This coupled with the
region at the minimum int he right rear quadrant of a 80+ knots upper
level jet...and possibly in a coupled upper jet region - depending
on the exact location of the subtropical jet. Models due vary on
the location/strength of the latter. 0-6 km bulk shear is forecast
to increase to 25-35 knots during the evening so there could be
sufficient shear/cape for isolated super cells during the evening
mainly across NYC/NE New Jersey/S CT/lower Hudson Valley zones. As such
there is the potential for strong to possibly severe storms
Wednesday night...mainly prior to 6z.
Models do differ on amount/extent of precipitation on Thursday due
to differences in timing of 850 hpa cold front. NAM/sref are the
slowest with this feature. Given the propensity for cold fronts to
hang up crossing the mountains...slower progression of the 850 cold
front makes some sense...so did weigh probability of precipitation and convective
probabilities more towards this line of thinking. However...there
should not be enough instability for any strong or severe storms on
Thursday. Have lingered slight chance probability of precipitation into Thursday evening
across far southeast zones...this might be a tad too long ultimately...but
with overall trend with frontal timing a tad slower than previous
forecast...cannot rule out precipitation lasting a tad longer than
See the hydrology section of the afd for rainfall amounts and
potential impacts from tonight into Thursday.
For lows Wednesday night used a blend of mav/met guidance with NAM
2-meter temperatures then added a degree to weigh towards warmer
solutions - with values forecast to be a few degrees above normal.
For highs Thursday used a blend of mixing down from 950-875 hpa per
BUFKIT soundings...with NAM 2-meter temperatures and a blend of
mav/met guidance...then added 2 degrees to weigh towards warmer
solutions. Expect highs to be around a few degrees below normal. For
lows Thursday night used a blend of mex/ekd/ece/ecm/wpc guidance
with NAM 2-meter temperatures - with values a few degrees below
The regions weather Friday-Monday will largely be determined by the
exact position/strength of a rather large cutoff low over eastern
Canada...and when spokes of energy rotating around its base pass
through the region. For now...it appears the region should be
between spokes Friday and Friday night and possibly into Saturday.
So for now have gone with a dry forecast from Friday-Saturday night.
However...there are some indications that a small shortwave could
pass the area on Saturday...possibly triggering some -shra on
Saturday. Confidence in this is too low to reflect in the forecast
at this time.
Based on model consensus...am more confident in a period of
unsettled weather Sunday...Sunday night and Monday. It will not rain
the entire time...in fact most areas will be dry for more time
during this time frame than it will rain at any given location.
Given difficulty in timing of shortwave rotating around a cutoff low
this far out...yet alone inherent uncertainty in models handling of
a cutoff low this far out...do not want to even attempt any sort of
timing - so have chance probability of precipitation Sunday-Monday.
For temperatures Friday-Monday used a blend of mex/ekd/ece/ecm/wpc
guidance with highs running below normal...and lows starting out
below normal and trending to near normal.
Aviation /15z Tuesday through Saturday/...
high pressure will slowly move offshore today. VFR with light
west/SW flow this morning.
Sea breeze late this morning into afternoon. Timing could be off +/-
1-2 hours from taf. Medium confidence sea breeze makes it to
kewr/kteb...resulting in wind direction around 170-180 true by late
A rain showers possible across interior late afternoon into early evening.
Confidence fairly low though...so only vcsh at kswf.
... 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: timing of sea breeze may be off +/- 1 hour.
Klga fcster comments: timing of sea breeze may be off +/- 2 hours.
Gusts indicated in taf may be more occasional in frequency.
Kewr fcster comments: medium confidence in sea breeze reaching
terminal this afternoon. If it does not...wind direction will stay closer
to 220 true.
The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.
Kteb fcster comments: medium confidence in sea breeze reaching
terminal this afternoon. If it does not...wind direction will stay closer
to 220 true.
Khpn fcster comments: timing of sea breeze may be off +/- 2 hours.
Kisp fcster comments: timing of sea breeze may be off +/- 1 hour.
Outlook for 12z Wednesday through Sat...
Wednesday...primarily VFR. Brief MVFR visibility possible early Wednesday...especially
interior and eastern terminals. Isolated rain showers/thunderstorm northwest of the New York
Wednesday night-Thu...slow moving cold frontal passage. MVFR or lower conds in
made minor changes this update to reflect the latest trends in
observations and guidance. Forecast appears on track.
Winds and seas are forecast to remain below Small Craft Advisory
levels of 25 knots and 5 feet through Wednesday morning. Occasional
gusts to 25 knots are possible on mainly the ocean waters Wednesday
Sustained winds up to 15 knots are likely Wednesday night ahead of a
cold front. For now appears gusts and seas should stay below small
craft thresholds. The pressure gradient then relaxes over the region
Thursday and remains light into Saturday. As a result expect winds
of 10 knots or less from Thursday through Saturday...with seas 4 feet or
less on the coastal ocean waters and 1 feet or less elsewhere.
mainly dry through Wednesday morning...though a brief locally
heavy downpour is possible in any stronger convection this
afternoon. This best chance for this is to the north/west of NYC.
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.