Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service New York New York
519 am EDT Friday Jul 29 2016

Synopsis...
low pressure over the Delmarva this morning passes to the south
and east of Long Island through this afternoon. High pressure will
then briefly build into the region tonight into the first half of
Saturday, giving way to low pressure approaching from the Ohio
Valley later in the day. This low will pass to the north as a few
waves of low pressure pass along a frontal boundary to the south
into early next week. High pressure then returns for the middle of
the week.

&&

Near term /until 6 am this morning/...
deep-layered lift with the approach of an upper jet and mid level
short wave trough this morning will result in a strengthening
frontogenetic band to the northwest of surface low pressure over the
Delmarva. Latest radar imagery shows band progressing across
eastern PA and central Maryland with localized heavy rainfall reports
across this area. Rainfall amounts up to 0.50 inches an hour were
noted across eastern PA.

Latest guidance has trended farther south with the low track and
thus the axis of heaviest rain which pivots across the area this
morning. There is good model clustering on keeping the heaviest
rain to the south of Long Island. That being the case, coastal
sections are still forecast to receive between 1 and 2 inches with
localized higher amounts. The biggest change in the forecast is
across the lower Hudson Valley and interior southern CT, where
less than an inch is expected on average. Thus,the Flood Watch
has been trimmed back and remains in place for NE NJ, NYC Metro,
Li, and coastal CT.

Precipitable water values around 2 inches with upper air soundings
typical of a tropical airmass. Narrow convective available potential energy support slowly rising
updrafts with mainly heavy showers and isolated thunderstorms.
Due to the farther south low track, severe weather is unlikely.

The heaviest rain will exit the area by late morning, perhaps
lingering across eastern Li and southeast CT into early afternoon.
Thereafter, there will be a chance of scattered showers and
possibly a thunderstorm, especially across the interior where
there will be some clearing.

Daytime highs will range from the upper 70s to lower 80s. It will
remain very humid with dew points around 70 and little change in
airmass on the backside of the low this afternoon.

&&

Short term /6 am this morning through 6 PM Saturday/...
weak ridging builds behind the shortwave tonight with surface
high pressure building from the northwest. Lows will be near
seasonable levels, but remaining muggy.

Weak high pressure will remain over the region Saturday morning,
resulting in a dry Saturday morning. Models have trended quicker
with the next approaching shortwave, which may trigger scattered
showers and thunderstorms as early as Saturday afternoon. Eastern
Li and southeast CT may be able to remain dry most of the day. Highs
also will be near seasonable levels.

&&

Long term /Saturday night through Thursday/...
latest nwp guidance in fair agreement with the 500 mb pattern across
North America consisting of strong high pressure over the southwest
US...a Bermuda high over the western Atlantic and a mean trough
extending from west of The Rockies to the East Coast this weekend.
Early next week the high out west expands back into the Southern
Plains sharpening the trough east of the Mississippi. The trough
moves east of the area on Tue with upper level ridging building in
for the middle of the week.

Model trends over the past 24 hours have sped up the weekend
system with pcpn moving in during the day Sat. The shortwave is
lagging behind the rrq of a 65kt upper jet...but could have decent
warm rain processes with pw's around 2 inches. However...the GFS
looks suspicious aloft between 00z and 12z developing a coupled
vort Max/min in the mid levels thus enhancing pcpn total at the
sfc. So...while there will likely be overrunning Sat night with a
frontal boundary to our south...the best dynamics associated with
the shortwave appear to pass to the north on sun with the majority of
the rainfall likely remaining to our north with areas north and west of NYC
having the best chance to see pcpn. A few weak waves of low pres
does develop along the boundary sun and Sun night...but they look
to pass too far S to have any real impact on the region. Have
remained with chc pops for most of the area during this time
except northwest zones which will be closest to the upper jet and
shortwave energy. There is also uncertainty with the location of
the frontal boundary. Ec is further north with it on sun tracking the
waves directly over the local area.

Upper trough axis approaches Mon and moves through Mon night with
sct showers/thunderstorms expected during this time. An isolated
shower is possible on Tue although there may not be enough
moisture and we could be capped as upper level ridging begins to
build in.

The remainder of the week looks dry with increasing heat and
humidity.

&&

Aviation /09z Friday through Tuesday/...
low pressure along the mid Atlantic coast will pass to the south
today. Associated heavy showers with IFR vsby are moving across
NYC Metro and are also along the New Jersey coast. Additional rain bands
with MVFR and local IFR vsby extend across the lower Hudson Valley
into northwest New Jersey and eastern PA. Think most of this activity will move
across NYC Metro between now and 14z-15z, and kbdr/kisp from 10z-
11z until about 15z-16z. LIFR conditions at kgon attm should
improve to IFR as rain arrives there early this morning and
continues until at least 16z. Isolated rumbles of thunder not
entirely out of the question, mainly at or near kisp.

Rain and MVFR conditions could linger a little longer than
outlined above, then improvement to VFR expected later this
afternoon.

NE winds could gust between 15-20 at the coastal terminals this
morning.

..NY 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: amendments possible to fine tune flight
category. Occasional g15-20kt possible this morning.

Klga taf comments: amendments possible to fine tune flight
category. Occasional g15-20kt possible this morning.

Kewr taf comments: amendments possible to fine tune flight
category. Occasional g15-20kt possible this morning.

The afternoon kewr haze potential forecast is yellow, which
implies slant range visibility 4-6sm outside of cloud.

Kteb taf comments: amendments possible to fine tune flight
category. Occasional g15-20kt possible this morning.

Khpn taf comments: amendments possible to fine tune flight
category.

Kisp taf comments: amendments possible to fine tune flight
category. Occasional g15-20kt possible this morning.

Outlook for 06z Saturday through Tuesday...
late tonight into Saturday morning...light fog with MVFR vsby
possible until about 12z-13z.
Saturday afternoon into Sunday...chance of showers and possibly a
tstm. MVFR or lower conditions possible.
Sunday night-Monday night...chance of showers. MVFR conditions
possible.
Tuesday...mainly VFR.

&&

Marine...
winds and seas are expected to remain below Small Craft Advisory
levels through Saturday. Low pressure is forecast to track south
of the waters today with strengthening east/NE winds through this
afternoon. Winds and seas are forecast to remain below sca, but
could gusts up to around 20 kt, especially on the ocean waters
east of Moriches Inlet. Winds diminish tonight as high pressure
builds across the waters.

Sub-advsy conds are then expected through the rest of the forecast
period.

&&

Hydrology...
a Flash Flood Watch is in effect for much of NE NJ, NYC Metro, Li,
and coastal for the potential of 1 to 2 inches with locally
higher amounts. The axis of heaviest rain at this time is expected
across eastern sections of Li and southeast CT.

The next chance for organized rainfall Saturday into Sunday.
Less than an inch is expected.

&&

Okx watches/warnings/advisories...
CT...Flash Flood Watch until 4 PM EDT this afternoon for ctz009>012.
New York...Flash Flood Watch until 4 PM EDT this afternoon for nyz071>075-
078>081-176>179.
New Jersey...Flash Flood Watch until 4 PM EDT this afternoon for njz004-006-
103>108.
Marine...none.

&&

$$
Synopsis...BC/met
near term...jp
short term...met
long term...British Columbia
aviation...Goodman
marine...BC/jp/met
hydrology...BC/met

National Weather Service Glossary of Abbreviations