Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kokx 210243 
afdokx

Area forecast discussion
National Weather Service New York New York
1043 PM EDT Thu Jul 20 2017

Synopsis...
mainly dry conditions are expected through Friday in the wake
of a cold front, however, hot and humid weather will continue.
A warm front will approach late Saturday and lift north across
the area into Sunday morning. Multiple waves of low pressure
move through the area through early next week, followed by
building high pressure for the mid to late week.

&&

Near term /until 6 am Friday morning/...
in the wake of the convective activity, patchy fog may form in
areas that received heavier rain and temps cool to near the
dewpoint.

Weak front has settled across eastern portions of the area late
this evening.

Lows tonight will still be in the upper 60s in the coolest
spots well north and west of the city with readings in the mid
to upper 70s in more urban areas.

&&

Short term /6 am Friday morning through Saturday night/...
west to northwest flow aloft sets up for Friday as the front
drifts on south and stalls toward the Delmarva Peninsula. Drier
air aloft should mix down a bit as the flow aloft remains
offshore to 925 mb. However, this flow aloft is light (10 kts or
less) that the seabreeze will likely return in the afternoon
which would bring dewpoints at the surface back up. With the
offshore flow I have favored the warmer end of guidance and
gone with the higher end of MOS. This will push temps to near 90
over well inland areas and into the low to mid 90s along the
coast and in and around immediate NYC and urbanized areas in
north Jersey. Thus the heat advisory was extended for most areas
today except for Rockland, Westchester, western Bergen and
southern Fairfield counties which look to fall just short of
criteria.

Although moisture and some instability lingers I have kept the
forecast dry as the presence of a Lee-side surface pressure
trough and seabreeze do not look to be enough to pop any lid to
trigger convection tomorrow.

Dry for Friday night with west/northwest flow aloft holding
firm. Lows should be a little cooler, with readings in the low
to mid 60s well north and west of the city to the mid 70s in NYC
and Hudson County, New Jersey.

I'm not enthused much for convection during the day on Saturday.
Westerly flow aloft sets up and a surface stationary front is
well to our south. Again, the only triggers will be the Lee side
surface pressure trough and the sea breeze. I left in a low end
slight chance of a shower or thunderstorm along the sea breeze
on Long Island and over interior areas where differential
heating of the hilly terrain may set off something. Highs will
be a bit cooler and many spots will only be in the 80s for a
high. However, humidity will still be enough to make it a sticky
Saturday.

The warm front should start to lift back north Saturday night
and return the potential for showers and thunderstorms from the
south and west. Models show a spread in timing, so I
broadbrushed in pops for this time frame. The better chance
should be closer to sunrise on Sunday as a low-level jet of
40 kts+ moves from the Jersey Shore toward Long Island. With
high precipitable water values approaching 2 inches per the GFS, the threat
for heavy rain will be there Saturday night along with gusty
winds in any more potent convection. Lows will be a little
warmer due to the increase in clouds and warm front lifting
north.

&&

Long term /Sunday through Thursday/...
much of the extended will be dominated by an unseasonably south
latitude polar jet orientation, with multiple short waves moving
through the northeast in northwest flow, which is typically a
pattern that offers very little predictability.

Despite considerable uncertainty for the extended period, the
pattern remains favorable for periods of heavy rainfall and
thunderstorms as multiple mesoscale convective systems move through
the area in northwest flow. The greatest complexity with the
forecast remains on where any frontal boundaries stall, which have
impacts on temperature, wind, instability, cloud cover, etc, but
most importantly on where exactly these systems will track. The
forecast will need to be monitored over the next few days for any
heavy rainfall/flooding and severe potential.

By mid week, a brief respite in the active wet pattern may come as
ridging builds aloft and confluent flow allows a surface high to
strengthen. At least briefly, dew points and subsequently relative
humidity values will finally fall to more comfortable thresholds.
However, this may be short lived as the overall pattern still looks
to be active.

&&

Aviation /02z Friday through Tuesday/...
VFR. Patchy fog and stratus may develop after 08z but confidence
is too low to include in terminals at this time.

West flow around 10 kt becoming light and variable overnight
before increasing again late Friday morning. By mid
afternoon Friday, some occasional gusts up to 20 kt possible at
coastal terminals.



New York 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: no unscheduled amendments expected. Patchy
fog and stratus may require an update late tonight.

Klga taf comments: no unscheduled amendments expected. Patchy
fog and stratus may require an update late tonight.

Kewr taf comments: no unscheduled amendments expected. Patchy
fog and stratus may require an update late tonight.

Kteb taf comments: no unscheduled amendments expected.Patchy
fog and stratus may require an update late tonight.

Khpn taf comments: no unscheduled amendments expected. Patchy
fog and stratus may require an update late tonight.

Kisp taf comments: no unscheduled amendments expected. Patchy
fog and stratus may require an update late tonight.

Outlook for 18z Friday through Tuesday...
Friday afternoon through Saturday...VFR.
Saturday night-Tuesday...episodes of showers and thunderstorms
with MVFR or lower conditions possible.

&&

Marine...
although winds and seas are forecast to remain below Small Craft Advisory (small
craft advisory) levels of 25 kt and 5 ft from overnight through
Saturday night, there is the potential for thunderstorms
Saturday night that could result in higher waves and winds.
Marine weather statements and/or special marine warnings are
possible during that time.

Depending on the exact track of the stalled front, southerly swells
may begin to increase through the weekend into early next week, with
a low probability for Small Craft Advisory conditions on the ocean by Monday.
Conditions will gradually improve by mid to late week as winds
decrease in building high pressure, allowing any lingering swells to
slowly subside.

&&

Hydrology...
a chance for flooding in periods of heavy rainfall and
thunderstorms will continue late Saturday night into Sunday and
Monday as a slow moving frontal system interacts with a moist
and unstable airmass.

&&

Climate...
today marked the 9th day of 2017 the temperature has reached at
least 90 degrees at Central Park.

So far we have had two heat waves (at least 3 consecutive days
of 90 degrees or greater) in 2017 at Central Park - from may
17th through may 19th and from June 11th through the 13th.

The highest temp of 2017 at the park has been 94 on June 13th
and today, July 20th.

Highest temps of 2017 for the other main climate stations in the
area as of 3:10 PM EDT today:

LaGuardia airport: 101 on 6/13
JFK airport: 94 on 6/13 and 7/20
islip: 93 on 6/13
newark: 99 on 6/13
bridgeport: 94 on 6/13

&&

Okx watches/warnings/advisories...
CT...none.
New York...heat advisory until 6 PM EDT Friday for nyz072>075-078-080-
176>179.
New Jersey...heat advisory until 6 PM EDT Friday for njz004-006-104>108.
Marine...none.

&&

$$
Synopsis...MD/cs
near term...pw/cs
short term...cs

National Weather Service Glossary of Abbreviations