Scientific Forecaster Discussion
fxus61 kokx 200006
Area forecast discussion
National Weather Service New York New York
806 PM EDT Sat Aug 19 2017
a weak cold front will pass through tonight, followed by high
pressure building from the west Sunday into Sunday night. The
region remains on the western periphery of the Bermuda high from
Monday through Tuesday. A cold front approaches from the west
Tuesday night then crosses the area on Wednesday. Canadian high
pressure then builds in through Saturday.
Near term /until 6 am Sunday morning/...
afd issued to clear rip current headline which expired at 8pm.
Latest radar trends show convection over central PA beginning to
weaken. 22z hrrr seems to be handling this well. Made some minor
adjustments in pops this evening, shading towards 22z hrrr
(ignoring its typical spurious convection out ahead of main
area). Should be dry throughout after midnight as northern
stream shortwave trough exits to the NE.
Low temperatures should be in the lower 70s in/just outside
NYC, with 60s elsewhere.
Short term /6 am Sunday morning through Sunday night/...
zonal upper flow ensues after the upper trough passage, with sfc
high pressure building from the west. Sunday should be mostly
sunny and quite warm, with high temps only a shade lower than
those of today. Temps should respond to clear skies/light winds
Sunday night by dropping into the 50s inland and in the Long
Island Pine barrens and the 60s most elsewhere, but only the
lower 70s once again in outside NYC.
Long term /Monday through Saturday/...
the region remains on the northern periphery of a western extension
of the sub-tropical ridge Monday-Monday night, with zonal flow
aloft. With no shortwaves embedded in the flow it should be dry with
minimal cloud cover. Any clouds would be primary some isolated-
scattered cirrus, but cannot rule out few-sct cu Monday
afternoon along any seabreeze/differential heating boundaries.
Highs Monday should be 5-10 degrees above normal, with the NYC Metro
area right around the 90 degree mark. With dewpoints progged in the
lower-mid 60s Monday afternoon, heat indices should be within a
degree or two of the air temperature. Lows Monday night should also
be around 5-10 degrees above normal, with urban heat island areas
only falling to the mid 70s.
SW winds aloft on Tuesday as an approaching north stream closed low
sharpens the flow ahead of it. GFS is the most aggressive of all
models with any showers/thunderstorms Tuesday afternoon, so have
limited pops to slight chance over the northwest 1/2 of the County Warning Area. Tuesday
will be another very warm-hot day over the area, with highs again 5-
10 degrees above normal. Afternoon dewpoints though should be around
70 producing heat indices across NYC/urban NE New Jersey in the mid 90s.
Have increasing pops Tuesday night into Wednesday with the
aforementioned northern stream closed low passing to the north, and
its associated surface cold front crossing the area on Wednesday.
With the region in the right rear quadrant of a 95-100kt 300 hpa jet
Wednesday, 1000-2000 j/kg of cape, 35-45kt of 0-6km bulk shear, and
the region in the tail of a 30-35kt low -level jet, there is a low-
end potential for strong to possibly isolated severe storms ahead of
the cold front on Wednesday. Lows Tuesday night should be a degree
or so warmer than on Monday night. Highs on Wednesday should be near
normal (depending on how fast the cold front actually moves through).
A mean trough sets up over the northeast and mid-Atlantic Wednesday
night-Saturday. However dry low levels and predominately northwest
(occasionally west-wnw) low level flow should keep things dry.
Temperatures should be near normal Wednesday night, then a few
degrees below normal Thursday-Saturday.
Aviation /00z Sunday through Thursday/...
a cold front moves through the terminals tonight followed by high
pressure for Sunday.
VFR through the taf period. Showers and thunderstorms to the west
will weaken and diminish after sunset with no impact to the
immediate New York Metro terminals. While a weakening shower/storm cannot
be ruled out at kswf 01-03z, have left out of taf due to low
SW-west flow this evening 10 kt or less veers to the northwest with the cold
front passage overnight. Northwest winds are expected on Sunday around 10
kt, with some backing to the west and SW in the afternoon.
Outlook for 00z Monday through Thursday...
Sunday night-Tuesday morning...VFR.
Tuesday afternoon-Wednesday...a chance of showers and thunderstorms
with MVFR or lower conditions possible. SW g20 kt possible late
made minor changes this update to reflect the latest trends in
observations and guidance. The forecast appears on track.
A relaxed pressure gradient over the region will limit winds to
around 10kt or less through Monday night, with seas/waves below
Small Craft Advisory levels.
The pressure gradient tightens ahead of a cold front Tuesday,
with winds up to around 15kt.
There should be a moderately tight pressure gradient over the
region Tuesday night- Wednesday with sustained winds up to
around 20kt and the potential for gusts to around 25kt,
especially over the coastal ocean waters. Seas should build to
Small Craft Advisory levels over the coastal ocean waters Tuesday night and
remain so on Wednesday.
The pressure gradient then slackens from Wednesday night into
Thursday. Winds should be limited to around 15 knots or less on
Wednesday night and 10kt or less on Thursday, with seas below Small Craft Advisory
levels during this time frame.
it should be dry through Monday night, then no significant
hydrologic impact is expected from any showers or thunderstorms
At this time, there is too much uncertainty to specify what, if
any, hydrologic impact would be experienced from convection
Tuesday night and Wednesday. It should then be dry Wednesday