Area Forecast Discussion
Issued by NWS Upton, NY

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KOKX 181516
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1116 AM EDT Mon Jun 18 2018

.SYNOPSIS...
A trough of low pressure builds in to western portions of the
Tri-State today, followed by a cold front crossing the area
tonight. Weak high pressure then builds in Tuesday and Tuesday
night before giving way to another cold front pushing through
the area Wednesday and Wednesday night. High pressure then
builds over the area through Thursday night then slides offshore
Friday and Friday night. Another frontal system impacts the area
this weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
A small decrease in clouds was made in the gridded forecast
database this morning with most observations within a few
degrees agreement with forecast values for temperatures and
dewpoints. The forecast overall remains on track.

WNW flow sets up aloft by this afternoon as the deep layered
ridge axis sinks to the SE. It should be dry this morning due to
subsidence from the departing ridge.

A weak 700-500 hPa shortwave trough moves into western areas
this afternoon, as a pre- frontal trough sets up over the Lower
Hudson Valley and NE NJ as well. The pre- frontal trough will
enhance low level convergence to the W and N of NYC with the
shortwave serving as a trigger to act on CAPEs progged in this
area of at least 1500 J/kg and around 30-35 kt of 0-6 km Bulk
Shear. Bulk Richardson numbers are fairly high (generally
greater than 70) so they do not support super cells and but
favor the possibility of multi- cellular convection out ahead of
the cold front. The NAM has been fairly consistent in
indicating this potential over NE NJ/Lower Hudson Valley late
this afternoon/early this evening over the past two nights. The
latest Convection Allowing Models (CAMs) are supporting this
idea as well, but a few hours faster. The GFS is a bit slower
than both the NAM and CAMs.

Based on this, agree with SPC in assessing a marginal risk for
Severe Thunderstorms over the Lower Hudson Valley, but would
think that the threat goes a bit farther S into NE NJ than they
indicate. Any severe storms over the Hudson Valley could
maintain themselves as they track into interior portions of S
CT Winchell, so there is a marginal severe threat there as
well. If there is any severe weather this afternoon/early
evening in the threat area, it will be due to damaging wind
gusts.

After this first round of convection, there should be a lull,
then there should be another round late tonight ahead of the
cold front. There is some question as to how well this
convection holds together as it moves into our marine dominated
airmass, so have capped pops at chance.

However, precipitable waters increase to around 2" this
afternoon and remain high until the cold front moves through. As
a result, there is the threat for locally heavy rainfall with
both rounds of convection. Refer to the hydrology section of the
AFD for details.

With the CMC-Global being alone in wanting to linger
precipitation into Tuesday, have opted for the faster timing of
a non-CMC-Global blend with the cold frontal precipitation.

Highs today should be around 10-15 degrees above normal. With
Interior areas and most of NYC reaching the upper 80s to lower
90s and some pockets of mid 90s passable in NE NJ and the Lower
Hudson Valley. It is this area that there is a high likelihood
of heat indices reaching 100 degrees this afternoon. As a
result, have continued the heat advisory from 15Z to 00Z for NE
NJ and the Lower Hudson Valley. Elsewhere heat indices should
top out in the 90s over the interior and most of NYC and in the
80s near the immediate coast.

Lows tonight will run around 10 degrees above normal.

There is a high risk of rip currents at Atlantic Beaches mainly
this afternoon and evening.

&&

.SHORT TERM /TUESDAY/...
NW flow at all levels will dry and clear things out fairly
rapidly.

Highs on Tuesday should be around 5 to 10 degrees above normal.
It likely will be warmer at coastal areas on Tuesday than
today, due to the lack of a seabreeze on Tuesday due to the NW
flow.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
NW flow aloft continues Tuesday night and with no shortwaves
progged to move through the area, it should remain dry with
minimal cloud cover.

The flow flattens on Wednesday as a northern stream closed low
builds into Quebec. As it does so, a shortwave rotating around
the base of this trough moves towards the area in the afternoon.
This could bring some spotty showers to mainly western zones
Wednesday afternoon. The axis of this cutoff low then crosses
the area Wednesday night, brining more widespread showers to
the entire area. In addition with showalter indices progged to
go to the 0 to 4 range, have added a slight chance of thunder
to the forecast as well. PRecipitable waters return to around
1.75 to 2 by late Wednesday, so locally heavy rainfall could
again be possible. See the hydrology section of the AFD for
details.

NW flow then returns to the region on the backside of the trough
Thursday and Thursday night. With relatively dry low levels,
both of these periods should remain dry.

Deep layered ridging builds in Friday and Friday night, with
associated subsidence keeping things dry.

A mean trough builds into the NE for the upcoming weekend with
unsettled weather the likely outcome - so should see a few
rounds of showers and possibly some rumbles of thunder as well
mainly from Saturday afternoon through Sunday.

Temperatures Wednesday-Sunday should generally be within a few
degrees of either side of normal.

&&

.AVIATION /15Z MONDAY THROUGH FRIDAY/...
High pressure to the south will give way to an approaching cold
front tonight.

Stratus continues to advect up the coast today. Will likely hold
right along the beachfront during the day light hours, but could
see occasional sct MVFR clouds this afternoon. Will have to
watch potential for it to come onshore at KISP or KGON with SCT-
BKN IFR cigs this evening.

Widely scattered tstms with brief MVFR/IFR vsby and gusty winds
are possible with a pre-frontal trough late today and early
this evening, most likely from about 20Z-22Z at KSWF, 21Z-23Z at
KHPN/KBDR, 22Z-01Z at the NYC metro terminals, and 00Z-02Z at
KISP. Since the expected coverage is scattered at most and not
guaranteed to have direct terminal impacts, have continued to
mention via VCTS rather than PROB30/TEMPO. Currently a low to
moderate confidence forecast on development and timing.

An additional round of showers/isolated tstms possible with the
front itself late tonight as it passes through.

S-SW flow will increase today, with sustained winds 10-15 kt
and gusts around 20 kt this afternoon and early evening. Sea
breezes at KJFK/KLGA/KISP could be stronger, with sustained
winds at or just over 15 kt and gusts approaching 25 kt.


...NY Metro Enhanced Aviation Weather Support...

Detailed information, including hourly TAF wind component fcsts,
can be found at: http:/www.weather.gov/zny/n90

KJFK TAF Comments: IFR/MVFR stratus should remain just SE of
the terminal radius through this afternoon. Occasional SCT cigs
possible. The afternoon KJFK haze potential forecast is YELLOW,
which implies slant range visibility 4-6SM outside of cloud.
Sparse convection possible this evening, btwn 23z and 02z.

KLGA TAF Comments: The afternoon KLGA haze potential forecast
is GREEN, which implies slant range visibility P6SM outside of
cloud. Sparse convection possible this evening, btwn 23z and
02z.

KEWR TAF Comments: The afternoon KEWR haze potential forecast
is GREEN, which implies slant range visibility P6SM outside of
cloud. Sparse convection possible this evening, btwn 23z and
02z.

KTEB TAF Comments: Sparse convection possible this evening, btwn
23z and 02z.

KHPN TAF Comments: Sparse convection possible this evening, btwn
23z and 02z.

KISP TAF Comments: A few IFR/MVFR cigs possible this morning,
cigs possible this evening. Sparse convection possible this
evening, btwn 23z and 02z.

.OUTLOOK FOR 12Z TUESDAY THROUGH FRIDAY...
.Tuesday...Sight chance of an early morning shower with MVFR
vsby, otherwise VFR. NW winds (right of 310 magnetic) 15G20KT.
.Tuesday night-Wednesday...VFR.
.Wednesday night...Chance of showers and possibly a tstm, with
MVFR or lower conds, as low pressure passes to the south.
.Thursday-Friday...VFR.

&&

.MARINE...
SW flow increasing 10-15 kt on the ocean with ocean seas up to
2 ft late this morning. Forecast remains mainly on track.

SW flow increasing to 15-20 kt late today, with near shore gusts up
to 25 kt late this afternoon and early this evening, warrants
issuance of SCA for the ocean waters and the Long Island south shore
bays. The SCA will continue through the night for the ocean E of
Fire Island Inlet, and into early Tue morning E of Moriches Inlet,
as those winds build max seas up to 5 ft during that time.

A wave of low pressure passing S of Long Island Wed night has some
potential to produce SCA conditions on the ocean waters. ECMWF
weaker with this wave as opposed to the stronger GFS, so have capped
winds and seas under SCA thresholds for now.

&&

.HYDROLOGY...
On average a few tenths of an inch of rain should fall over the
area this afternoon and tonight. However, given the expected
abundant low level moisture, there is the potential for locally
heavy rainfall with any given storm. As a result, there is the
potential for minor flooding, especially for an area
experiencing repeated storms producing locally heavy rainfall.

No significant, widespread hydrologic impacts area expected
from Tuesday and Tuesday night.

Locally heavy rainfall is again possible Wednesday afternoon and
night, with minor flooding possible yet again. There is still
some uncertainty on how much the average rainfall will be from
this system, so the possibility of localized flash flooding
cannot be 100% ruled out at this time.

No significant widespread hydrologic impacts are expected
Thursday and Friday.

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off
the air for an extended period of time.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Heat Advisory until 8 PM EDT this evening for NYZ067>071.
     High Rip Current Risk until 9 PM EDT this evening for NYZ075-
     080-081-178-179.
NJ...Heat Advisory until 8 PM EDT this evening for NJZ002-004-006-
     103>108.
MARINE...Small Craft Advisory from 3 PM this afternoon to 9 PM EDT this
     evening for ANZ345-355.
     Small Craft Advisory from 3 PM this afternoon to 9 AM EDT
     Tuesday for ANZ350.
     Small Craft Advisory from 3 PM this afternoon to 6 AM EDT
     Tuesday for ANZ353.

&&

$$
SYNOPSIS...Maloit
NEAR TERM...JM/Maloit
SHORT TERM...Maloit
LONG TERM...Maloit
AVIATION...Goodman/NV
MARINE...JM/Goodman
HYDROLOGY...Maloit
EQUIPMENT...


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.