Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 281819
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
219 PM EDT THU JUL 28 2016

.SYNOPSIS...
Weak high pressure offshore, moves farther east through this
afternoon. A wave of low pressure approaches and passes nearby
Friday. High pressure briefly builds into the region for Saturday.
Unsettled weather returns Sunday and Sunday night with the passage
of another low pressure system. Drier weather is expected for the
first half of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
The region will lie between a closed low over Northern Quebec and
Southeastern US ridging today...with zonal upper flow gradually
backing to the SW ahead of a broad trough digging east of the
Mississippi River.

A hot and humid air mass remains over the region today. There is
the potential for heat indices across NYC metro/NE NJ and Lower
Hudson valley to peak in the mid to upper 90s this afternoon. A
few spots across NE NJ could flirt with 100 degrees in the
afternoon as a sea breeze works inland and increases
dewpoints...however this will be sparse. Southerly flow along the
coast will promote early sea breeze development and should cap
temps in the mid to upper 80s along south coasts.

Weak shortwave energy moving through aloft and ample moisture
could spark an isolated shower/tstm along the sea breeze boundary
late morning into afternoon. Limited instability...potentially
capped at mid-levels...should keep any tstm development pulsey and
sub-severe.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Models in good agreement with a southern wave over the Lower
Mississippi River Valley getting picked up by a digging Upper
Mississippi River Valley/Great Lakes trough today...and then sliding
ne towards the area Friday. At the surface...developing low pressure
along a stalled frontal boundary over the Tennessee River Valley
tonight...track ne towards the region Friday morning. Models are
converging on a track in the vicinity of the region on Friday...but
still subtle differences in terms of timing and track will present
a significant mesoscale forecast challenge.

Synoptic lift...interacting with deep gulf moisture of 2 to 3 stds
above normal...instability feed from the south...and focus for
convergence along the warm front/coastal front ahead of the
approaching low will provide the ingredients for heavy rainfall
during the late tonight through into Friday afternoon period.

To the north of the track of the 850 hpa low...models indicating a
moderate to heavy frontogenetic rain band with a little if any
convection. Operational and ensemble depicting potential for 1 to 3
inches within this swath over a 6 hr period.

Along and just on the cool side of the warm front back to the triple
pt...potential exists for not only elevated convection...but surface
based. This would pose both a flash flood threat and lesser severe
threat. Threat for flash flooding from training convection as
steering flow closely parallels warm front. The GFS/NAM initialized
SBU WRF is depicting swaths of 7 to 10 inches along this boundary
due to training convection...but location is quite varied. This is a
concerning signal, and cant be ignored based on the available
instability and moisture. The limited severe threat appears to be
for weak tornadoes based on strong veering wind profile...low
lcls...low-level cape...and sufficient low-level shear/helicity in
se inflow.

Unfortunately the exact mesoscale setup will likely only become
clear as the event nears tonight into early Friday morning. So where
exactly these threats line up is still quite uncertain. Would like
to let dayshift evaluate some of the ensemble cams before issuing a
flash flood watch. Will continue to address the flash flood
and convection threat in HWO.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Latest NWP guidance in fair agreement with the H5 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.
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.

The only timeframe that looks to have organized pcpn is
late Saturday night into Sunday night. Currently looks to be an
overrunning event with a wave of low pres tracking along an old
frontal boundary to the south of Long Island. However...there are
some indications that the low track could be further north so this
will need to be monitored. Upper support is not impressive
though...with only a 40kt jet streak and weak vorts so not
anticipating a high impact event.

Otherwise...pcpn moves out Friday evening with dry weather on
Saturday with high pressure moving across. There`s also the
potential for isolated showers/tstms during the first half of next
week...mainly N and W of NYC during the aftn hours.

Temps will be near normal levels through the period with highs in
the 80s and lows generally in the 60s to lower 70s.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
...High Impact Weather Forecast until 18z Friday...

Low pressure is forecast to gradually intensify as it moves northeast
across the area Friday.

Widespread IFR conditions in heavy rain and fog with embedded thunderstorms
are forecast north of the low`s track across the Lower Hudson
Valley and CT, mainly between 06z and 16z Friday.

There is a potential for thunderstorms with damaging wind gusts along
and south of the lows` track along coastal NJ, NYC, and
Long Island.

Weather conditions improve from west to east 18z-23z Friday.

     NY Metro Enhanced Aviation Weather Support...

Detailed information including hourly TAF wind component fcsts can
be found at: http:/www.weather.gov/zny/n90

KJFK TAF Comments: G20kt possible 20Z-23Z.

KLGA TAF Comments: Brief G15-18kt possible 21Z-23Z.

KEWR TAF Comments: Slight chance of a TSTM aft 22Z. Brief G15-18kt possible
20Z-22Z.

The afternoon KEWR haze potential forecast is green, which implies
slant range visibility 7SM or greater outside of cloud.

KTEB TAF Comments: Slight chance of a TSTM aft 22z. Brief G15-18kt possible
20Z-22Z.

KHPN TAF Comments: No unscheduled AMD.

KISP TAF Comments: No unscheduled AMD.

.OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY...
.Friday Afternoon...MVFR improving to VFR as rain ends west to east
by 23z.
.Friday night until Noon Saturday...VFR.
.Saturday Noon into Monday Night...Chance of showers/tstms with
MVFR or lower conds.
.Tuesday...Mainly VFR.

&&

.MARINE...
Visibilities across the ocean waters continue to improve as the
fog has become less widespread or dissipated. Fog may redevelop
late this afternoon into the evening. However, at this time
widespread dense fog is not expected.

Sub sca conds expected today as weak high pressure slides
offshore. 20 kt gusts possible in NY bight and adjacent nearshore
waters late today.

Marginal se sca gusts possible on ocean waters if low pressure
tracks north of the waters late tonight/Fri morning. Marginal N/NE
gusts possible on ocean waters if low tracks to the south. In
addition...seas may build to marginal sca levels Friday afternoon
into Fri Night as southerly swells work in.

Marginal SCA conds may be met Fri night as the low departs but
should fall back below by morning. Sub-advsy conds are then expected
through the rest of the forecast period.

&&

.HYDROLOGY...
There is potential for significant rainfall of 1-3 inches, with
locally several inches of rain from late tonight into Friday
afternoon with a low tracking near the area. Potential exists for
flash flooding from training convection along a warm front,
dropping several inches of rain in a short period of time. Farther
north of the warm front, rain would be mainly stratiform and
result in mainly minor urban and poor drainage flooding.
Unfortunately the exact location of these scenarios may not become
clear until the event nears tonight, so continue to monitor the
latest NWS forecasts for updates on this flooding threat.

The next chance for organized rainfall is Sunday. Although exact
amounts are unclear at this time, they should be less than
an inch.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Flash Flood Watch from 8 PM EDT this evening through Friday
     afternoon for CTZ005>012.
NY...Flash Flood Watch from 8 PM EDT this evening through Friday
     afternoon for NYZ067>075-078>081-176>179.
NJ...Flash Flood Watch from 8 PM EDT this evening through Friday
     afternoon for NJZ002-004-006-103>108.
MARINE...None.

&&

$$
SYNOPSIS...24/NV
NEAR TERM...MET
SHORT TERM...NV
LONG TERM...24
AVIATION...GC
MARINE...24/MET/NV
HYDROLOGY...24/NV



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