Scientific Forecaster Discussion
fxus61 kokx 271812
Area forecast discussion
National Weather Service New York New York
212 PM EDT Thu Jul 27 2017
high pressure will remain off the coast today, while a cold
front slowly approaches from the northwest. The front will enter
the area tonight and become stationary on Friday. Low pressure
developing late Friday into Friday night over the Ohio Valley to
the mid Atlantic coast will move slowly south of the region
Saturday into Saturday night. Canadian high pressure will build
in from Sunday into the middle of next week.
Near term /until 6 PM this evening/...
1230 PM update:
well - as said previously... a challenging forecast for late
afternoon/early evening. Have updated based on radar trends and
Convective showers are moving into central CT/the lower Hudson
Valley and eastern PA as of 1615z. Pure advection brings this
to NYC/Long Island by 18z. With hrrr struggling with the now-
term, have updated pops to likely for this afternoon.
Instability is marginal at best with MLCAPE only about 500
j/kg and deep layer shear of 30 knots. Going with slight chance of
tstms as a result.
High temps should be in the upper 70s/lower 80s, slightly
warmer than a MOS blend and still a few deg below avg.
There will be a moderate risk of rip currents at area beaches.
Short term /6 PM this evening through 6 PM Friday/...
1230 PM update: no changes at this time. Have updated the severe weather potential statement
product, but planning to hold off on a Flood Watch (would be
overnight Friday into Saturday morning) for now.
Expect the front to enter the area tonight and then stall. An
associated bkn trailing line of showers/tstms also expected
this eve, moving across from northwest-southeast and impacting southern CT and
the lower Hudson Valley more than other areas. These storms
will have better instability to work with, with MLCAPE closer to
1000 j/kg, so a marginal svr risk could last into the first
half of tonight, with stronger cells possibly producing gusty
winds and small hail.
Lows tonight will be in the lower 70s near the coast, and
mid/upper 60s inland.
Precip with approaching low pressure should hold off until
Friday night. However, there could be enough low level
convergence along the old frontal boundary to spark isold-sct
showers/tstms in the afternoon, particularly invof NYC Metro
where there the sea breeze could focus convergence further.
High temps on Friday will be a seasonable lower/mid 80s.
Long term /Friday night through Wednesday/...
a shortwave across western Canada will be moving over the
western ridge and into the northern plains and Great Lakes
region Thursday and Friday. This shortwave will dig a trough
into the eastern United States later Friday into Friday night
with a surface low developing across the Ohio Valley to the mid
Atlantic. The trough will dig to the Gulf of Mexico coast and
into Florida by Saturday with the upper low closing off over the
mid Atlantic states. This will keep a rather prolonged period of
precipitation across the region. The uncertainty is how far
north the upper low will be when the low closes off and also
where the surface low will be. This will determine where a
deformation zone sets up and where the cutoff of the
precipitation will be. A cold pool will also be moving into the
mid Atlantic states Friday night into Saturday increasing lapse
rate with the potential for a series of thunderstorms. In
addition moisture will be transported into the region from the
Gulf of Mexico with precipitable water values increasing to over
2 inches late Friday night into Saturday. A low level jet will
enhance lift and there will be the potential for periods of
heavy rainfall from late Friday night into Saturday.
The upper low lingers along the mid Atlantic coast through the
weekend, however much of the energy with the low will be
offshore, so precipitation is expected to wind down Sunday.
Ridging builds into the area later Sunday through the middle of
next week, the the Atlantic high returning by mid week. After a
cool start to the week temperatures and humidity are expected
to increase for the mid week period.
Aviation /18z Thursday through Tuesday/...
a weakening cold front approaches from the northwest this
evening and passes through the terminals during the early
morning hours Friday. Developing low pressure over the Ohio
Valley then approaches from the southwest late Friday into
Friday night, passing to the south on Saturday.
There will be occasional MVFR ceilings this afternoon along
with some showers through tonight. Any thunderstorms are
forecast to be isolated in nature.
A period of MVFR/IFR conditions is forecast overnight as winds
become light and variable for a time ahead of the cold front.
Conditions improve around daybreak with the onset of daytime
S/SW winds 5 to 10 kt this afternoon become light and variable
overnight, and then light NE toward daybreak following the cold
New York Metro enhanced aviation weather support...
Detailed information, including hourly taf wind component forecasts,
can be found at: http:/www.Weather.Gov/zny/n90
Kjfk taf comments: occasional MVFR ceilings this afternoon.
Klga taf comments: occasional MVFR ceilings this afternoon.
Kewr taf comments: occasional MVFR ceilings this afternoon.
Kteb taf comments: occasional MVFR ceilings this afternoon.
Khpn taf comments: occasional MVFR ceilings this afternoon.
Kisp taf comments: MVFR ceilings possible this afternoon.
Outlook for 18z Friday through Tuesday...
Friday night-Saturday...MVFR or lower with heavy rain and
possibly a tstm. NE winds g25-35kt on Saturday, mainly at the
quiet through Friday afternoon outside of any tstms. A
strengthening northeast to east flow will occur Friday night
into Saturday, with wind gusts increasing to small craft levels
Saturday and ocean seas building to 5 feet or greater by late
Saturday. Small craft winds will continue into late Saturday
night, and there is a chance that gusts could occasionally reach
gale force on the ocean waters Saturday night. Small craft
ocean seas are expected to remain into Monday. With high
pressure across the region winds and seas will then remain below
Small Craft Advisory levels Monday night through Tuesday.
there is the potential for a heavy rainfall event Friday night
through Saturday, especially across portions of northeastern New
Jersey, New York City and Long Island. From Friday night through
Saturday night rainfall is expected to range from around 1/2 to
3/4 of an inch across the lower Hudson Valley and interior
southern Connecticut to 1 1/4 to 1 1/2 inches across
northeastern New Jersey and across Long Island. Local amounts of
2 to 2 1/2 inches are possible. Urban and poor drainage flooding