Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
435 am EDT Thursday Jul 28 2016
weak high pressure slides offshore today. 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
Hot and humid conditions today...with highs in the lower to mid 90s
across the interior. Heat indices across NYC Metro/NE New Jersey amd lower
Hudson Valley will likely run in the mid to upper 90s. A few spots
across NE New Jersey could flirt with 100 degrees in the afternoon as sea
breeze works inland and increases dewpoints...but appears to 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
Stratus advecting in off the ocean this morning...expected
to overspread Li and southeast CT through daybreak. Patchy fog possible
along south coastal areas. Expect stratus to mix out fairly quickly
after daybreak with strong heating.
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
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 severe weather potential statement.
Long term /Friday night through Wednesday/...
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.
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 north and west 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 /09z Thursday through Monday/...
light southerly flow at city terminals overnight with light and
variable winds at outlying terminals. Winds will become southerly at
most terminals daytime Thursday, and increase to around or just over
10 kt near the coast in the afternoon with sea breeze enhancement.
Exceptions to the rule will be klga, with an east-northeast morning sound
breeze, and kewr/kteb, where southeast sea breezes close to 10 kt expected
mid to late afternoon.
Low clouds have spread onto Long Island, impacting kisp. Light west-southwest
flow has kept these clouds away from kjfk, but will still have to
watch out for backbuilding toward the terminal before 12z. The flow
may also spread these clouds to kgon for a brief time
Cannot totally rule out an isold shower or tstm this afternoon,
mainly near sea breeze boundaries on Long Island. Kisp could
experience brief vicinity impact.
..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: low cloud deck with IFR cigs could briefly build
westward before 12z. G20kt possible 20z-23z.
Klga taf comments: no unscheduled amend expected. Brief g15-18kt
Kewr taf comments: no unscheduled amend expected. Brief g15-18kt
The afternoon kewr haze potential forecast is green, which implies
slant range visibility 7sm or greater outside of cloud.
Kteb taf comments: brief g15-18kt possible 20z-22z.
Khpn taf comments: no unscheduled amend.
Kisp taf comments: no unscheduled amend expected.
Outlook for 06z Friday through Monday...
late tonight...MVFR vsby possible in showers.
Friday...IFR likely in showers/tstms. Rain heavy at times. Tstms
could produce strong winds in the morning NYC Metro terminals and
Friday night...becoming VFR.
Saturday night into Sunday night...chance of showers/tstms with
MVFR or lower conds.
sub sca conds expected today as weak high pressure slides offshore.
20 kt gusts possible in New York bight and adjacent nearshore waters
Marginal se sca gusts possible on ocean waters if low pressure
tracks north of the waters late tonight/Fri morning. Marginal north/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 Small Craft Advisory 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.
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 National Weather Service 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