Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 230625
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
225 AM EDT Sun Jul 23 2017

.SYNOPSIS...
A frontal boundary remains to our south tonight as a wave of
low pressure tracks along it. This front then sags farther to
the south later today after the low passes. Another low then
moves along the front, tracking off the mid-Atlantic coast by
Monday morning. Still another area of low pressure that moves
through the region Monday and Monday night, exits to the east
Tuesday. High pressure builds over the northeast late Tuesday
through Wednesday, then drifts off the coast Wednesday night.
Another wave of low pressure follows for Wednesday night into
Friday, with a cold front moving through Friday. High pressure
returns Saturday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Forecast remains generally on track. Heavier showers have
developed in and around NYC, but this activity is progged to
pass east early this morning. Once a mid and upper level
shortwave exits, some drying should occur except for possibly
some lingering showers mainly over Long Island.

Lows tonight should be around 5 degrees above normal.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
The region should be under locally zonal flow Sunday. With no
shortwaves of note forecast to move over the region in this
flow, it should be mainly dry. However, this is quite a change
from the previous forecast. So to trend things, went with
slight chance pops over western zones and mainly dry over
eastern zones through late afternoon, then increased pops to
chance over far western zones and slight chance throughout
elsewhere (reflecting climatological trends for convection).

A sharpening 700-500 hPa trough/developing closed low moving
into the Great Lakes Sunday night, along with 850 hPa
frontogenesis, will produce an increasing threat of showers,
with a slight chance of thunderstorms. The pops increase from W
to E, to likely throughout by after midnight.

Onshore low-level flow should result in a mostly cloudy sky on
Sunday, limiting highs to near to slightly below normal levels
(mainly around 80-mid 80s). Lows Sunday night should be slightly
above normal due to cloud cover.

There is a moderate risk for the development of rip currents at
ocean beaches Sunday.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
An upper level shortwave and accompanying wave of surface low
pressure will be exiting to the east Monday night into early
Tuesday. Showers and isolated thunderstorms will be on-going at the
beginning of the extended forecast period. Instability and CAPE will
be marginal and increase somewhat during Monday, however may still
not be sufficient to support widespread convection, so will keep
isolated wording.

The upper westerly flow will be progressive through the period. A
weak ridge builds Monday night into Tuesday, and Wednesday. Then
another shortwave, with an embedded closed low, over the Canadian
west coast Monday, opens and digs a more significant trough into
the eastern states Wednesday night into Thursday with a high
amplitude trough, of 1 to 2 standard deviations above normal,
digging all the way to northern Florida by Friday. The flow looked
to be still progressive with a surface low moving through
Thursday and Friday. However, there are hints that the upper low
will close off again Friday into Saturday and remain along the
northern coast into next weekend. At this time will keep with
persistence and the more progressive flow and keep Friday night
into Saturday dry as upper ridging builds to the north.

Temperatures through the extended period will be near to slightly
below seasonal normals.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
A frontal boundary will remain just south overnight as a wave
of low pressure tracks along it, then sag farther south today
after the low passes. Another low will then moves along the
front tonight.

Brief IFR vsby in heavier rain at KJFK has tapered off, leaving
MVFR conditions in rain at KISP. Lingering MVFR conditions at
KEWR/KTEB should improve overnight.

Expect BKN VFR cigs through the day on Sunday, with NE flow
turning SE in the afternoon. Played cigs more on the pessimistic
side, but they could be higher than forecast if drier air works
in from the NE, especially at the CT terminals. If the more
optimistic scenario plays out, winds at coastal terminals could
be more southerly then fcst as a sea breeze also develops.

As the next low approaches, showers with MVFR conditions should
make it to the NYC metro terminals after 02Z-03Z Mon.

.OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY...
.Late Sunday night-Monday night...Showers likely. MVFR conds
likely, IFR cigs possible. A rumble of thunder also possible
late Sunday night.
.Tuesday...Mainly VFR.
.Tuesday night-Wednesday night...VFR.
.Thursday...Chance of showers and possibly a tstm, with local
MVFR or lower conds.

&&

.MARINE...
A light to moderate pressure gradient over the waters around
Long Island through Sunday night, will limits sustained winds
to 15 KT or less, ocean seas to 4 ft or less, and seas/waves on
the non- ocean waters to 1 ft or less through then.

Winds, gusts, and seas will remain below small craft levels Monday
through Thursday. However, ocean seas may approach 5 feet Wednesday
night into Thursday as an increasing southerly flow develops ahead
of a cold front. Waves of low pressure passing through the waters
will bring a chance of thunderstorms Monday and again Thursday into
Thursday night.

&&

.HYDROLOGY...
Currently expecting up to an inch in spots across southern
portions of the CWA and less than 1/4 of an inch of rainfall
elsewhere through morning.

An additional 1/2 to 1 inch of rainfall is likely from Sunday
night into Monday night, with locally higher amounts possible.
There is a small chance for minor flooding or urban and poor
drainage areas, if any experience locally heavy rainfall.

More rain is possible late Wednesday night through Friday.
Significant hydrologic impacts are not expected at this time.

&&

.TIDES/COASTAL FLOODING...
With the approach of the new moon (Sun), tides will run high
this weekend into early next week. Positive tidal departures of
1/2 to 1 ft will be needed for minor flooding during the night
time high tides during this time.

Minor flooding is possible starting with the high tide cycle
this evening, mainly in the western south shore bays of Long
Island. A bit more widespread minor flooding is possible Sunday
night with an E/NE flow expected. The threat for minor flooding
could continue into Monday, with E/NE flow progged to continue.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

&&

$$
SYNOPSIS...Maloit/MET
NEAR TERM...BC/Maloit/MET/PW
SHORT TERM...Maloit
LONG TERM...MET
AVIATION...Goodman
MARINE...Maloit/MET/PW
HYDROLOGY...Maloit/MET
TIDES/COASTAL FLOODING...



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