Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 300201
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1001 PM EDT SUN MAY 29 2016

.SYNOPSIS...
High pressure over the western Atlantic gradually translates
eastward tonight ahead of a frontal system working east from the
Ohio Valley. A pre-frontal trough will work into the area by
daybreak Monday and then dissipates across the area. A cold
frontal passage will then follow late Monday night into Tuesday
morning. High pressure then returns until a cold front slowly
approaches at the end of the week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Fog and stratus remains across Long Island and southern portions
of Queens and Brooklyn this eve. It continues working its way
westward through srn ct...although there is some uncertainty just
how far west it will get. Clouds will lower and thicken across
the rest of the area overnight anyway as pcpn moves in from the
south. May need a dense fog advsy on Long Island and portions of
srn CT for a bit tonight...although once the heavier rain moves
in...this should scour out. Will monitor. Have slowed down timing
of likely pops mainly over eastern areas based on latest radar and
hi res model data. Also made some adjustments to sky/t/td to
better reflect current conditions and trends.

High amplitude ridge over the western Atlantic finally weakens
and translates east tonight in response to an upper trough lifting
NE across the Great Lakes and into eastern Canada. This allows the
westerlies along the northern tier of the country to expand
eastward and allow for a more progressive flow. As this happens,
tropical moisture rounding the western periphery of the ridge, as
well as moisture associated with TD Bonnie over south Carolina
will get drawn northward ahead of an approaching cold front and
pre-frontal trough. With the aforementioned upper trough lifting
out to the NE, the RRQ of the upper jet will press east overnight
along with a surface trough. Deep-layered moisture with PW values
increasing to around 2 inches will interact with multiple lifting
mechanisms for widespread showers to develop late tonight.
Marginal instability will also allow for isolated thunderstorms.
There is the potential for localized heavy rainfall with many
locations seeing upwards of an inch by daybreak, especially from
NYC points north and west.

There is some uncertainty with the magnitude and location of
convection along ahead of the approaching pre-frontal trough
overnight. This is also leading to uncertainty with location of
heaviest rainbands and thus the qpf axis. The GFS is most
aggressive across the interior of the Lower Hudson Valley with the
ECMWF to a lesser extent. The NAM WRF primarily focuses the
strongest convection across the coastline. The GFS of late has
grossly exaggerated the diurnal convection. How this translates
forward with a synoptic scale system remains uncertain, but due to
the tropical connection with this system have leaned toward the
higher model QPF of the GFS.

Overnight lows will remain mild in the 60s with dew points not far
behind. This is above normal by about 10 degrees.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Deepest lift and moisture in the morning will be primarily from
NYC and points east. In fact, model time height cross sections
show drying in the low-levels but continued mid and upper level
lift with the upper jet dynamics and mid level frontogenesis.
Heaviest rain is forecast to end over all but eastern LI/SE by
early afternoon, where it could linger a few more hours.

Models have trended a bit slower the last couple of days with the
evolution of this system. This is something to bear watching.
Showers are forecast to linger through much of the afternoon.

Localized flash flooding is a possibility during the morning/early
afternoon hours with any embedded thunderstorm activity. Showers
very well could linger into the nighttime hours, especially across
LI/CT as some mid level energy associated with TD Bonnie shears
NE into the Mid Atlantic Region. This will be watched closely with
the potential for more significant rainfall.

As for highs Mon, stayed on the cooler side of the MOS guidance
with highs generally in the lower to mid 70s. Lows will remain
mild in the lower to mid 60s.

There is a moderate risk of rip current development at Atlantic
facing beaches on Tuesday.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Models are in good agreement with the H5 pattern across north
america through Wed...but then timing and amplitude differences with
the next trough/cutoff low traversing southeast Canada during the
second half of the week is impacting the progression of a cold front
across the area.

12z EC still holding on to residual pcpn Tue morning therefore have
maintained schc pops. Although tropical depression Bonnie will
still be over coastal north Carolina...the focus for pcpn will
have passed e with all pcpn remaining offshore. NHC`s 11am advsy
tracks Bonnie to around 100 miles SW of the 40N 70W benchmark at
12z Friday. Due to its close proximity there could be a few showers
Thu mainly across srn portions of the forecast area. As the front
moves closer Thu night and Fri...showers and tstm chances will
increase...although it now appears that additional moisture from
Bonnie or its remnants will remain separate from the approaching
frontal boundary. If the upper trough associated with this
boundary speeds up however...this could change.

This upper trough digs as it moves through the Midwest/Ohio valley
leading to a slow progression of the sfc front across the area.
While the forecast has pops from Thu Night through Sunday...think
most of the activity will be diurnal.

Temperatures will remain above normal levels Tue and Wed...with a
return to near normal temps thereafter.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Conditions range from VFR at most of the western terminals to IFR
at KJFK/KBDR and LIFR at both KISP and KGON. Some uncertainty how
far wwd this gets...although conds should also deteriorate at
remaining terminals later tonight along with showers moving in
from the SW. The timing of when this occurs is what is in
question. Have pushed it off until 05z for now...but this still
may not be enough.

Rain showers will increase after 05Z and become heavy at times
near daybreak into the morning hours. There could be some
improvement to MVFR for Monday PM for some western terminals with
otherwise IFR or below continuing. Rain showers...heavy at times
continue through much of Monday especially east of the city
terminals. Any thunderstorms will be isolated.

.OUTLOOK FOR 00Z Tuesday through Friday...
.Monday Night...MVFR/IFR possible with a chance of showers.
.Tuesday...Becoming VFR.
.Tuesday Night-Wednesday night...VFR. E-NE winds g15-20kt
Wednesday.
.Thursday-Friday...Low chance of MVFR or lower in showers. E-NE winds
g15-20kt Thursday.

&&

.MARINE...
A dense fog advsy remains in effect for all waters tonight with
higher dew point air over the cooler coastal waters. There is
likely areas of drizzle occurring as well.

A persistent southerly flow will continue on the waters around
the western periphery of the western Atlantic ridge. Seas will
gradually build through Tuesday with the possibility of marginal
SCA seas late Monday night into Tuesday. There is quite a bit of
uncertainty on how much residual swell from Tropical Cyclone
Bonnie will impact the coastal ocean waters early next week.

Wind gusts could approach sca levels on the ocean on Thu.
Otherwise sub-advsy conds are expected through the remainder of
the forecast period.

&&

.HYDROLOGY...
For tonight through Monday Evening...a widespread 1 to 1.5 inches
of rain is forecast. Locally higher amounts are a good
possibility. This rain could lead to minor urban and small stream
flooding and there is chance for localized flash flooding as well.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Dense Fog Advisory until 6 AM EDT Monday for ANZ330-335-338-
     340-345-350-353-355.

&&

$$



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