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Area forecast discussion 
National Weather Service New York New York
228 PM EDT Friday may 29 2015

Synopsis...
high pressure will set up over the Atlantic through Saturday. A
cold front approaches Saturday night and moves through the region
on Sunday. The front will stall just south of the area as weak
waves of low pressure ride along it. High pressure then builds in
from the north late Tuesday into Wednesday...shifting south of the
area on Thursday.

&&

Near term /through tonight/...
no major changes made with the latest update. The forecast is on
track. Hi pressure ridge drifts through the County Warning Area today and offshore by
evening. Northerly flow this morning will therefore gradually veer to
the S today. Water vapor shows a very dry airmass building over
the area...so will forecast a mainly clear sky through tonight. The
return flow however will allow for increasing humidity due to the
low level moisture influx...and with the dry middle levels some
patchy fog will be possible tonight.

Temperatures were close to a blend of guidance as the numbers were in
good agreement. However...there is the potential for some locally
higher temperatures today particularly over Long Island if the opposing
northeasterly flow holds the sea breeze back a bit. The namdng
suggests near 80 along roughly the 495 corridor. As a result
bumped up highs in this area a few degrees.

&&

Short term /Saturday/...
destabilization by afternoon across western zones with south-southwest flow. This
will again keep eastern portions of the County Warning Area...especially the
coasts...stable. The NAM hints at temperatures remaining in the 60s
across the S shore of Long Island and much of coastal CT.
Although this may be a bit much...did lower temperatures in this area and
will bank on a stable airmass. Across the west...the main question
will be whether there will be a sufficient trigger. The jet will
be too far upstream...but the models do hint at some subtle middle
level forcing. Maintained the current chance probability of precipitation for the afternoon
hours across approximately the western 1/3 of the County Warning Area.

&&

Long term /Saturday night through Thursday/...
western Atlantic ridge weakens slightly at the start of the long
term period Saturday night with heights beginning to fall over the
area. This will allow a cold front to approach from the northwest.
The best chances for showers and thunderstorms will be north and
west of New York City early Saturday night...and then probability of precipitation increase
from west to east late Saturday night as the front draws closer.

The front should be entering the interior Sunday morning and moving
south through the remainder of the area during the late morning and
early afternoon hours. Models generally agree on this scenario
although it is possible the timing slows down in later runs as the
models can be too fast moving fronts south with deep ridging off the
coast. The front does have a good push south however with a near
1030 mb high over the Great Lakes region and a shortwave moving
across southeast Canada and northern New England.

Probability of precipitation increase to likely from northwest to southeast across the area Sunday morning
into the afternoon. With abundant cloud cover and
precipitation...instability will likely be low. Have continued the
wording from previous forecast with showers likely with a chance of
thunderstorms. A deep moisture feed around the ridge tapping into
the Gulf of Mexico brings high precipitable waters ranging from 1.5
to 1.8 inches. Locally heavy rainfall is possible with any showers
in this airmass.

Showers continue Sunday night into Monday as the front stalls just
south of the area. Weak waves of low pressure will ride along the
boundary. Aloft...some short wave energy...and the region being
located near the right entrance region of a 80-100 knots upper level
jet across northern New England and southeast Canada provide a
larger scale lifting mechanism. Locally heavy rainfall remains a
possibility through at least Monday morning. Probability of precipitation will slowly taper
to high chance in the afternoon for northern zones...but remain
likely across the south.

Probability of precipitation continue trending downward Monday night into Tuesday morning.
However...models differ on the handling of a more well defined short
wave at 500 mb late Monday night into Tuesday. The 00z European model (ecmwf) is
slower and indicates a more neutral tilt which allows widespread
shower activity to continue well into Tuesday. The GFS and CMC shift
the front further south with a positively tilted shortwave quicker
to move through. Will need to see if the European model (ecmwf) is on to something as
the new 00z run is consistent with its previous 12z run. For
now...forecast shows a low chance probability of precipitation for southern zones Tuesday
morning but these may need to be increased if the models come more
into line with the European model (ecmwf).

High pressure will build into the region Tuesday night through
Wednesday...and then shift south into the western Atlantic on
Thursday. This will allow for drier conditions to return.

Temperatures will be near normal on Sunday...average below normal
Monday through Wednesday...and be near normal on Thursday.

&&

Aviation /18z Friday through Wednesday/...
high pressure remains offshore through Saturday with a cold front
approaching from the Great Lakes. This will keep the area under a
prolonged period of southerly flow.

Forecast dilemma resides in the extent and magnitude of
stratus/fog development tonight. Latest Sat imagery shows area of
stratus 40-50 miles south of Li. This will begin returning north
this after as winds becomes southeast...and may reach the South Shore
between 00z and 03z. The offsetting factor with be the amount of
dry air over land. Thus...have delayed IFR/MVFR conditions until
after 06z tonight...and then quickly improve to VFR after 12z Sat.

New York metropolitan enhanced aviation weather support...

Detailed information...including hourly taf wind component forecasts
can be found at: http:/www.Erh.NOAA.Gov/zny/n90 (lower case)

Kjfk fcster comments: timing of stratus along the South Shore
could move in earlier this evening.

Klga fcster comments: no unscheduled amendments expected.

Kewr fcster comments: no unscheduled amendments expected.

Kteb fcster comments: no unscheduled amendments expected.

Khpn fcster comments: no unscheduled amendments expected.

Kisp fcster comments: timing of stratus along the South Shore
could move in earlier this evening.

Outlook for 18z Saturday through Wednesday...
Saturday afternoon...most likely VFR. Chance of MVFR in
showers/thunderstorms mainly to the north/west of city terminals. Gusts
to 20-25kt possible with seabreeze.
Saturday night-Tuesday morning...MVFR or lower at times in
showers. Thunderstorms possible Saturday night-Sunday night.
Tuesday afternoon/night...becoming VFR.
Wednesday...VFR.

&&

Marine...
hi pressure will keep winds and seas below Small Craft Advisory levels through tonight. S
flow increases through the day on Sat with Small Craft Advisory conditions possible
by late afternoon...especially the ocean and S shore bays.

Small Craft Advisory conditions are likely on the ocean waters from Saturday night
through Tuesday. A cold front will be approaching Saturday night
with strong southerly flow ahead of it. Seas on the ocean will be
near 5 feet and winds could gust up to 25 knots. The front crosses the
waters on Sunday with a strengthening NE flow behind it. Seas likely
build up to 7 feet on Monday and continue into Tuesday on the
ocean.

&&

Hydrology...
the potential continues for an extended significant widespread
rainfall...mainly Sunday through Monday with a cold front stalling
near the region. It is difficult to specify exact rainfall
amounts...but there will be potential for heavy rainfall especially
Sunday and Sunday night into Monday morning when precipitable waters
reach 1.5 to 1.8 inches. Any heavier showers produce locally heavy
rainfall and therefore at least minor flooding of urban/poor
drainage areas will be a possibility. Localized flash flooding
cannot be ruled out.

&&

Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...none.

&&

$$

Synopsis...jmc/ds
near term...jmc/Goodman/ds
short term...jmc
long term...ds
aviation...dw
marine...jmc/Goodman/ds
hydrology...ds

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