Area Forecast Discussion
Issued by NWS Upton, NY-- Highlight Changed Discussion --
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FXUS61 KOKX 290458
Area Forecast Discussion
National Weather Service New York NY
1258 AM EDT Sat Apr 29 2017
A series of weak fronts cross the region tonight into Saturday
night. High pressure will return briefly for Sunday. A warm
front will then approach from the south Sunday night, and lift
into or through the area on Monday, followed by a cold front
from the west Monday night into early Tuesday morning. Weak high
pressure will return for the rest of Tuesday into Wednesday. A
low pressure system will then approach on Thursday, and pass
nearby on Friday. Weak high pressure then builds in through
Wednesday. A frontal system approaches from the southwest
Thursday and moves along the coast through late week.
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Minor adjustments were made again to the forecast database to
reflect the observed trends mainly with temperatures and
dewpoints. Lower and thicker clouds are expected late tonight
as the chances for showers and thunderstorms increase ahead of
the warm front. With coherent Showalter index forecast agreement
between different models with slightly negative values,
elevated instability is conveyed, and hence the potential will
be there for thunderstorms. The coherent mesoscale reflectivity
fields show higher reflectivity forecast in the 09-12Z timeframe
in the region. The forecast precipitable waters increase to
near 1.6 to 1.7 inches briefly early Saturday morning with the
convection so brief locally heavy rain will be possible
especially with any thunderstorms.
Through this evening high pressure will remain across the region
as Bermuda high pressure remains in the western Atlantic. This
keep a south to southwest flow across the area with increasing
dew points tonight. A warm front will be developing after 03Z
from low pressure across the central plains. There will be
increasing lift and instability mainly aloft late tonight and
into Saturday morning. In addition a weak vort will travel along
the developing warm front. This is expected to trigger showers
and a chance, or scattered embedded thunderstorms late tonight,
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
The front will remain in the area into early Saturday morning
and then dissipate as the Bermuda high builds back into the
area, leaving a warm and humid, summer like airmass in place.
Also, the vort moves quickly east of the region by 15Z, may be
sooner as depicted in some short term guidance. Afterward expect
area to remain dry, although both the NAM and GFS hint at some
precipitation heading close to the area late Saturday afternoon.
More likely is that maybe scattered showers develop on the
periphery of the high late in the day. Despite rain and clouds
early in the day, high temperatures expected to be close to
Friday highs, a couple of degrees lower, as sunshine develops
and with mixing to 900-850 MB. The boundary, cold front then
gets push south late Saturday night as high pressure builds to
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Remarkably consistent trend to the long term, so changes to the
previous forecast have been minor at most, except perhaps for Sunday
into Monday. Temps have trended a little cooler for Sunday after the
back door cold frontal passage, with highs from the upper 50s to mid
60s, warmest west of the Hudson. Precip with the approaching warm
front looks to be on the light side, but do expect widespread low
clouds to develop, also some patchy fog late Sunday night into
Monday morning just ahead of the warm front. Depending on the
strength of a lobe of high pressure off to the east and the
potential for a weak wave of low pressure to develop along the
front, it may take some time for the front to lift north of the
area, especially across Long Island and southern CT, so there will
be a wide range of potential high temps on Monday. High temp
forecast is close to the 00Z ECMWF ensemble mean MOS, with 60s
across southern CT and most of Long Island, and 70s west of there.
That said, the high end ensemble numbers suggest lower 80s are
possible west of the Hudson, and widespread 70s farther east, if the
front lifts through by afternoon.
At any rate, a cold front should move through Monday night into
early Tuesday morning with showers and a few thunderstorms, followed
by dry wx for the rest of Tue into Wed, with temps running above
average especially on Tue, with upper 60s to mid 70s, then mid and
upper 60s on Wed.
As noted a couple of days back, chances for rain will increase late
this week as flow aloft becomes zonal at first, then more amplified
via a developing upper trough in the Central states. The resulting
deep layer SW flow in its advance should result in surface
cyclogenesis along a baroclinic zone over the southern Plains and
lower Mississippi Valley, with this low then moving up the coast
toward the area and tapping into Gulf and Atlantic moisture. This
has some potential to be a heavy rain maker on Friday if the
synoptic scale ingredients are in sync, but it is still too early to
know for certain.
.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
A weak cold front settles over the area tonight...with a wave of
pressure moving through early Saturday morning. The cold front
slowly sags south of the region late Saturday.
An area of showers with embedded tsra will approach from the
west overnight, and should pass through from 8-14Z, west to
east. Medium to high confidence in sparse coverage of
tstms...conveyed through a VCTS.
The other concern is potential for IFR/LIFR
stratus/fog...currently lurking offshore...working back into
KJFK/KISP/KGON after 06z. Elsewhere MVFR or IFR conditions are
possible in fog and showers late tonight into Sat morning. Once
these showers move through by late Sat morning, VFR conditions
Light s or variable winds overnight...eventually turn toward
the W/SW by late morning Saturday. Westerly gusts to 25-30 kt
likely for KLGA/KEWR/KTEB/KSWF Sat aft. South coastal terminals
likely to see winds backed more to the SW...with gusts 20 to 25
kt in the afternoon. Winds should eventually veer to wnw late
.OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY...
.Saturday Night-Sunday...VFR...then MVFR cigs possible late
Sunday. Winds veering from NW to E/NE Sat night. E/SE gusts 15
to 20 kt Sun aft.
.Sunday night-Monday...MVFR or lower possible in showers and
.Monday night...MVFR in showers/possible thunderstorms. LLWS
-- Changed Discussion --Long period south to southeast swell between 3 and 5 feet
continues on the ocean waters. The combination of wind wave and
swell was allowing for seas to still fluctuate around 5 feet
mainly on the waters east of Fire Island Inlet. Seas and swell
will be slow to subside tonight and could fluctuate between 4
and 5 feet. The small craft advisory for hazardous seas remains
in effect until 09Z for the waters east of Fire Island Inlet.
Winds and seas will then be below advisory levels until later
Saturday afternoon as a south to southwest flow strengthens and
seas build once again on the ocean waters. Then seas subside
Saturday evening as winds diminish.
With the current small craft advisory in effect will not issue
one for Saturday at this time.
Increasing easterly flow between a warm front approaching from the
south and high pressure off to the northeast could push ocean seas
up to 5 ft late day Sunday into Sunday evening.
Still high confidence in increasing S-SW flow pushing ocean seas
above 5 ft early next week, most likely by Mon night head of a cold
front, and lasting into at least Tue night if not Wed as moderate
post-frontal WSW flow continues. Could see gusts up to 25 kt there
late Mon night into Tue afternoon, with seas peaking at 5-7 ft Tue
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No hydrologic impacts are expected through Thursday.
A low pressure system approaching from the southwest could
offer potential for heavy rain and hydrologic impact on Friday,
but it is too early to know for certain.
-- Changed Discussion --CT...None.
MARINE...Small Craft Advisory for hazardous seas until 5 AM EDT early
this morning for ANZ350-353.
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