Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 200334
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1134 PM EDT Fri Apr 19 2019

.SYNOPSIS...
Low pressure slowly approaches tonight and Saturday from the
west. This slow moving system does not exit until the beginning
of next week. A cold frontal passage is expected during the
middle of next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Not much change from previous forecast. POPs as well as
temperatures and dewpoints were slightly adjusted to better
match observed trends. One larger area of showers with embedded
heavier showers and possible thunderstorms set to move into
western parts of the region between 12AM-2AM. Wind gusts
increased slightly along the southern coasts of Long Island and
southern parts of NYC.

Longwave trough closes off, then cutoff low over southern states
makes slow progress northeast tonight. Deep surface low pressure
over the southern Appalachians moves northeast, but weakens slightly
overnight. Deep southerly flow, strong WAA and elevated instability
will set the stage for increasing coverage of showers, with thunder
possible as well.

Very warm air advects northward and patchy fog remains possible
tonight in spite of strong south winds. Temperatures will fall
slightly this evening, then remain nearly steady overnight.
Will maintain the Flash Flood Watch. Convection should result in
local higher amounts, whereas other locations could see under
an inch.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Stacked low makes very slow progress east, and sfc low will weaken
quite a bit per model consensus during this time frame.

Convection over the area in the morning is expected to make eastward
progress during the day and into the night. Spotty showers remain a
possibility behind the main area of showers behind the higher
coverage in the afternoon and at night.

Do expect thunder chances in the morning with the main area of
convection. A midlevel dry slot will quickly move across the
area suppressing convection to the west closer to the upper low
center.

With clouds in place, low level inversion should preclude widespread
readings in the 70s, unless more sunshine is realized in the
afternoon. Did lean toward the higher end of guidance just in
case, but strong southerly flow will keep eastern areas
(particularly srn CT and LI) much cooler.

South winds weaken late in the day and at night, and temps should
remain quite mild in the 50s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Early in the period the upper level portion of the storm that
impacts the region in the near and short term portion of the
forecast will be over the region. Looking for a general shower
chance to begin the period with a closed upper level feature which
is progged to gradually fill, weaken, and lift out by Monday night.
Until then thought it best to keep general shower chance across much
of the CWA. With the upper level low over the area and some
instability present cannot rule out an isolated thunderstorm later
in the day on Monday, especially with any breaks of sun. In the wake
of the departing upper level system a brief period of soft ridging
will attempt to work in for late Monday night and into the day on
Tuesday. The thinking for Tuesday is to keep the region generally
dry with good agreement among the global models on timing.

The next system is progged to approach during Tuesday night and
early Wednesday. There could be enough energy aloft and enough low
level moisture to at least bring a period of chance showers to the
region for Tuesday night into Wednesday morning. There may be enough
instability depending on timing / time of day on Wednesday that a
thunderstorm or thundershower cannot be ruled out. Most of the
modeling has been consistent with the timing of this feature, with
the German ICON model having a few runs with precip hanging in for a
part of Thursday. This is at odds for the most part with the other
global deterministic models and mass fields, therefore will keep
Thursday dry for now with high pressure building in. WPC discussion
does however point out uncertainty next week with individual
shortwaves tracking across the Midwest into the Northeast. This has
lead to variability among the various global ensemble suites. So
confidence is lower than desired for later next week.  For now have
leaned towards high pressure being in control by late Wednesday or
Wednesday night through much of Friday as the NAEFS 500 mb forecast
suggests an increase in progression with the northern branch.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Widespread IFR/MVFR ceilings and low-level wind shear through
the overnight as a slow moving frontal band works into the area.

There appears to be multiple episodes of showers and possibly a
thunderstorm during the night with the next batch approaching
the terminals between 04Z and 06Z, and then gradually
transitioning east. Due to the slow progression, the band may
take up to a few hours to pass each location. However, showers
are likely to linger behind the front into the afternoon,
especially east of the NYC terminals.

A strong low-level jet across the area will result in a
prolonged period of LLWS with winds of 45 to 55 kt at 1500-2000
ft, strongest NYC and east. S winds at the surface of 15-20kt
with G25-30t. Winds gradually back to the S-SE on Saturday
behind the front. Due to a strong low-level inversion, gusts may
be less frequent at times.

.OUTLOOK FOR 00Z SUNDAY THROUGH TUESDAY...
.Saturday Night-Sunday...MVFR or lower in a chance of showers.
.Monday...MVFR or lower in a chance of showers.
.Tuesday...VFR. Slight chance of showers late in the afternoon.
.Wednesday...MVFR or lower possible in showers.

&&

.MARINE...
Marine forecast generally on track but did increase slightly
wind gusts across the ocean and NY Harbor as well as South
Shore Bays.

Strong southerly winds will continue tonight, 20-30 kt, ahead of low
pressure. These winds will slowly diminish Saturday, likely falling
below 25 kt threshold for SCA during the afternoon. These southerly
winds diminish further at night as the pressure gradient relaxes,
with weakening low pressure to the west.

Ocean seas will remain rough through Saturday night, so SCA will
remain up through that time.

Southerly flow diminishes Saturday night into Sunday as low pressure
weakens as it approaches the waters. With the diminished flow with
low pressure over the coastal waters a period of patchy fog may
occur for late Saturday night into early Sunday morning. Seas will
remain up on the ocean waters due to a south to southeasterly swell,
therefore SCA conditions will continue through the weekend and into
early next week on the ocean waters. Meanwhile, sub SCA conditions
are expected for the non-ocean waters through the early part of next
week. Sub SCA conditions may finally return by Tuesday afternoon on
the ocean waters as seas subside below 5 ft.

&&

.HYDROLOGY...
Rain totals tonight and Saturday should range from a half an
inch in spots, to locally 2 inches, with the best chance for
higher QPF east of NYC into Srn CT and LI. Due to high
precipitable waters, deep southerly flow, and lift, the flood
watch remains in effect.

Otherwise, no hydrologic impacts are expected for the second
half of the weekend into the end of next week.

&&

.TIDES/COASTAL FLOODING...
Isolated minor tidal flooding is possible for overnight for Long
Island Sound shorelines along Southern Westchester and
Southwest Connecticut.

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO35 (162.55 MHz) remains off
the air.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Flash Flood Watch through Saturday evening for CTZ006>008-
     010>012.
     Flash Flood Watch through Saturday afternoon for CTZ005-009.
NY...Flash Flood Watch through Saturday evening for NYZ078>081.
     Flash Flood Watch through Saturday afternoon for NYZ067>075-
     176>179.
NJ...Flash Flood Watch through Saturday afternoon for NJZ002-004-
     006-103>108.
MARINE...Small Craft Advisory until noon EDT Saturday for ANZ330-335-
     338-340-345.
     Small Craft Advisory until 6 AM EDT Sunday for ANZ350-353-355.

&&

$$

SYNOPSIS...JE/PW
NEAR TERM...JM/PW
SHORT TERM...PW
LONG TERM...JE
AVIATION...DW
MARINE...JE/PW/JM
HYDROLOGY...JE/PW
TIDES/COASTAL FLOODING...JM
EQUIPMENT...


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