Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1039 PM EDT Thursday Aug 21 2014
an upper level disturbance pushes through the northeast into the
weekend...eventually pushing south on Saturday as high pressure
builds down from eastern Canada. This high will remain nearly
stationary over the northeast into Tuesday...then will shift south
of the area and slide offshore through Thursday.
Near term /until 6 am Friday morning/...
showers and thunderstorms around the city....associated with an
upper level trough pivoting through the northeast...will continue
to wind down over the next few hours due to the loss of heating. Laps
data indicating the activity enters a more stable airmass. Have
adjusted probability of precipitation and weather grids based on latest radar data and
trends. There is lower confidence in probability of precipitation across eastern Li and southeast
CT with the storms weakening in the more stable atmosphere.
Because of this...capped probability of precipitation at chance for the second half of the
night. Any thunderstorms over the County Warning Area at this point would be
Temperatures right around normal tonight. Used a blend of met/mav
Short term /6 am Friday morning through Friday night/...
the region remains positioned under the deepening trough along the
eastern Seaboard as ridging aloft strengthens across the central
US. At the surface...low pressure rides a nearly stationary front
well south of the area...with high pressure dipping south from
southeastern Canada. Some model discrepancy on the extent of precipitation
development during the day and exactly where it forms. Once
again...higher confidence of development over western areas where
a shortwave is expected to move through as it rounds the
trough...so maintaining the higher chance probability of precipitation there...with slight chance
over eastern areas with the thinking that the persistent easterly
flow will work to stabilize the atmo and minimizing the chance for
shower formation. 12z model suite also suggests the stronger
forcing with another shortwave remaining well east of the area
tomorrow afternoon into tomorrow evening...keeping the bulk of that
associated precipitation east of the area.
For tomorrow night...could see lingering showers mainly over
western areas...clearing by 06z as high pressure at the surface
nudges south. Patchy fog also possible with plenty of moisture being
injected in the lower levels by the easterly flow. Temperatures on the
cooler side again with the onshore flow during the day Friday as
well into Friday night.
There is a moderate risk for rip current development along the
Atlantic Ocean beaches during the day Friday.
Long term /Saturday through Thursday/...
models are in good agreement that the 500 mb pattern across noam at the
start of the long term period will consist of an amplifying ridge
extending from south central Canada through the southeast Continental U.S. With a
cutoff low over the western US a slowly weakening blocking pattern
over eastern Canada and the northeast. The anomalously strong ridge
over Quebec will gradually break down and merge with the
aforementioned ridge over the US. This will result in a digging
trough east of New England.
Some uncertainty with the specific details and timing of vorticity energy
tracking through New England on Sat...but the trough axis should
move through Sat night. Have kept the majority of Sat dry with just
a schc of showers early. There could be a few additional showers
during the afternoon if there are any weaknesses aloft...but cannot
pinpoint where and when at this Point. May need to add slight to low
chance probability of precipitation in subsequent forecast packages to account for these timing
differences. Additionally...the amount of cloud cover on Sat is
also questionable as a result.
Otherwise...expect dry seasonable conds through the middle of next
week as heights rise once the trough departs. Surface high pressure will
build into the northeast over the weekend and remain nearly
stationary into Tuesday. This will result in an Ely flow contributing
to below normal temperatures though this time...but with heights
rising Tuesday through Thursday...temperatures will rebound to near normal
Aviation /03z Friday through Tuesday/...
weak low pressure moves through the area overnight and off the
Delaware-Maryland-Virginia Friday morning. High pressure builds from the northeast
during Friday. Showers and an isolated thunderstorm will impact the
NYC area terminals through 05z...with a chance of showers east of
Marginal VFR ceilings will be likely...mainly along the coast...with
a chance of marginal VFR visibilities in fog. There will be some
improvement after 14z with VFR visibilities and ceilings possibly
lifting to VFR.
Southeast wind 5 to 10 knots will gradually back to the east after 06z
and remain east to northeast through Friday.
Outlook for 00z Sat through Tuesday...
Friday night-Sat...marginal VFR ceilings and possibly visibilities in
fog into Saturday morning...then improving to VFR.
generally sub-Small Craft Advisory conditions on the waters through Friday night
with high pressure building south and low pressure remaining well
south of the waters.
Small Craft Advisory for seas will be possible on the ocean waters Sat with a
moderate Ely flow. Current forecast keeps seas just below Small Craft Advisory
levels...but there is the potential for them to be a foot or so
higher. Sub-advsy conds expected thereafter as the pressure gradient
weakens with high pressure building over the northeast.
showers with a few slow moving thunderstorms producing locally heavy
rainfall will continue this evening in interior NE New Jersey and into
parts of NYC. Only expect minor urban and poor drainage issues at
No significant rainfall is then expected through the middle of