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Area forecast discussion 
National Weather Service New York New York
435 am EDT Thursday Jul 30 2015

Synopsis...
a cold front approaches the region today and moves across tonight.
Weak high pressure follows for Friday. Multiple weak cold fronts
or troughs will move across the area starting Saturday night and
continuing into the middle of next week. The strongest cold
frontal passage looks to be on Tuesday afternoon. In
between....weak high pressure will prevail across the area.

&&

Near term /until 6 PM this evening/...
the cold front at the surface will be approaching today with a
continued southwest flow ahead of it. This will continue the warm
and moist air advection. Precipitable waters grow up to near 2-2.2
inches...allowing for heavy rain potential with any shower or
thunderstorm that forms. The convection will further develop and
expand in the afternoon with the closer proximity of the front and
colder air aloft. More of a cyclonic flow aloft arrives with a
digging trough into the northeast.

In terms of hazards...heat advisory remains in effect. Heat indices
came close to 100 degrees elsewhere along the urban corridors of
northeast New Jersey...southern lower Hudson Valley as well as
southwest Connecticut. However...with expectation of increasing
clouds and increasing likelihood of showers and thunderstorms...kept
temperatures and heat indices slightly lower than otherwise.

Overall though a hot and humid day again in store. This will fuel
the cape which will be pretty substantial...up to near 2000 j/kg
mainly north/west of NYC. Models also show 0-6 km bulk shear of 20-25 knots.
Models are showing expansive clouds across the region which will
limit the heating and instability. However...if there is more
sunshine than forecast...more areas could potentially reach heat
index of 100 degrees.

Used the warmer met guidance for highs.

There is a high risk of rip currents at ocean beaches today.

&&

Short term /6 PM this evening through 6 PM Friday/...
convection ongoing across Long Island early this evening as the cold
front moves across. This will dissipate late in the evening into the
overnight as the bulk of convection moves southeast of Long Island
with the front. A shortwave in the middle levels pivots around the
longwave trough as moves north of the region through the night.

The weather will be dry Friday as weak high pressure builds in from
the south and west. The source region of the next airmass will be
across the south central U.S. A continued very warm but now drier
airmass will build in. Dewpoints lower to upper 50s to lower 60s for
much of the region with more of a west to northwest flow.

&&

Long term /Friday night through Wednesday/...
a rather benign period with a broad upper trough across eastern
Canada and the NE quarter of the nation. Polar vortex during this
time descends from Hudson Bay on Sat southeast into Ontario province by middle
week. A series of disturbances in the upper flow will send weak cold
fronts or troughs across the area with the potential for scattered
convection. MDT instability...decent middle level lapse rates...and
some wind shear supports isolated strong convection. The limiting
factor will be moisture with a deep-layered west/SW flow.

Temperatures during the period will be several degrees above normal...but
overall the airmass will be drier than recent days...so a little
less humid. Temperatures on Wednesday may be overdone a bit as the GFS is
significantly cooler with a sharper trough and cold front passing
through late Tuesday. European model (ecmwf)/ggem are considerably flatter and warmer.
Subsequent tends in global model runs will be watched. Gefs supports
warmer solutions.

&&

Aviation /09z Thursday through Monday/...
a southerly flow continues around high pressure off the
middle Atlantic coast as a cold front through the Great Lakes and into
Ohio slowly approaches.

Generally VFR through the morning...although isolated MVFR possible
in developing br/hz. Several pieces of guidance indicating widely
scattered shower activity developing over central/northern New Jersey between 09z and
12z and tracking to the NE through 15z or so. Have included vcsh
at most terminals to account for this...but would like to see
something on radar before adding it into prevailing or tempo. A
few showers popped up over the past hour in southeast PA...but are
weakening as they move Ely.

The cold front and a weak pre-frontal trough will be moving into the
terminals around 18z today and move through this evening. Scattered
showers and thunderstorms will accompany the front with MVFR
conditions...or possibly IFR in stronger storms. There is a higher
chance of convection from the NYC terminals and areas west. Have
added tempo groups for the two hour period with highest
likelihood of thunderstorms...but this may need to be adjusted slightly.

Heavy rain will likely accompany any showers this morning and
especially in thunderstorms this aftn/eve. This will drop visibilities to IFR or
lower in the heaviest activity.

Moderate to high confidence in wind forecast.

New York 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: gusts up around 20 knots possible after 15z. Timing
of thunderstorms may be +/- 1 to 2 hours.

Klga fcster comments: gusts may be a few knots higher than forecast.
Timing of thunderstorms may be +/- 1 to 2 hours.

Kewr fcster comments: gusts may be a few knots higher than forecast.
Timing of thunderstorms may be +/- 1 to 2 hours.

The afternoon kewr haze potential forecast is green...which implies
slant range visibility 7sm or greater outside of cloud.

Kteb fcster comments: gusts may be a few knots higher than forecast.
Timing of thunderstorms may be +/- 1 to 2 hours.

Khpn fcster comments: occasional gusts around 20 knots possible late
morning/aftn. Timing of thunderstorms may be +/- 1 to 2 hours.

Kisp fcster comments: gusts may be a few knots higher than forecast.
Timing of thunderstorms may be +/- 1 to 2 hours.

Outlook for 06z Friday through Monday...
Thursday night...MVFR possible conds in fog/haze becoming VFR.
Friday-Monday...VFR.

&&

Marine...
BUFKIT exhibits pretty good agreement with gusty winds across
much of the waters this afternoon into early this evening.
Wavewatch currently verifying within a foot of buoy observation. The ocean
seas increase to 5 feet this afternoon in response to continued
southerly fetch and south to southeast swell. The Small Craft Advisory seas last
through tonight. A return to sub Small Craft Advisory conditions will be in place
for Friday into Saturday as weak high pressure moves in.

Ocean seas could build to around 5 feet Sat night...and then again
late Monday into Tuesday ahead of an approaching cold front. Prevailing
flow will be S/SW during this time.

&&

Hydrology...
basin average quantitative precipitation forecast of approximately 1/2 inch possible through
tonight...likely across interior areas and locations near NYC and
to the north and west. With precipitable water over 2 inches...locally heavy
rainfall is possible with any stronger convection. Minor
urban/poor drainage flooding is the most likely outcome. There
will also though be a possibility of flash flooding but expect
this to be more isolated.

Otherwise...no significant widespread rain expected.

&&

Okx watches/warnings/advisories...
CT...none.
New York...heat advisory until 8 PM EDT this evening for nyz072>075-176-
178.
High rip current risk through this evening for nyz075-080-081-
178-179.
New Jersey...none.
Marine...Small Craft Advisory from 2 PM this afternoon to 8 PM EDT this
evening for anz330-340-345.
Small Craft Advisory from noon today to midnight EDT tonight
for anz355.
Small Craft Advisory from noon today to 6 am EDT Friday for
anz350-353.

&&

$$
Synopsis...jm/dw
near term...jm
short term...jm
long term...dw
aviation...24
marine...jm/dw
hydrology...jm/dw

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