Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 191635
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1235 PM EDT Thu Apr 19 2018

.SYNOPSIS...
Low pressure passes to east of Long Island this afternoon,
then quickly exits into the Canadian Maritimes tonight through
Friday as it deepens. High pressure slowly builds in from the
Great Lakes Friday night through Sunday night, then gradually
slides offshore from Monday through Tuesday night. A coastal low
approaches from the southeastern seaboard on Wednesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Forecast on track with the greatest chance of rain this
afternoon to the south and east of the Lower Hudson Valley as
low pressure deepens offshore and an upper trough approaches
from the west. Any rainfall will be light. Additionally, with
northerly winds on the backside of the low, temperatures will
likely not rise much more, remaining around 40 inland and the
lower 40s at the coast.

North winds will back around to the northwest late and become
gusty as the pressure gradient becomes tighter between the low
and strong high still well out west into the Central Plains.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
The main upper level jet will remain south of the region through
Friday.

For tonight:

Two more shortwaves pivot across the region in the mid levels. So
despite the surface low moving farther away to the south of Nova
Scotia, the region will remain in cyclonic flow aloft. The chances
for precipitation while much lower than earlier in the day,
will be still be present mainly during the evening. Cold air
advection on the backside could result in a light rain/snow mix
across some parts of the interior, especially higher terrain. No
snow accumulation is expected. Otherwise, the precipitation
will end as rain.

For overnight, more drying takes over with the persistent NW
flow.

With the abundant clouds, used a blend of guidance in terms of
temperatures including the previous forecast. There will be
some cold air advection but without ideal radiational cooling.
Winds stay up so despite temperatures in the mid 30s for those
parts of the region in the growing season, not expecting frost
formation.

For Friday:

In the mid levels, the mid low will be moving east of the region,
allowing for heights to build as ridging commences from well to the
west.

The same pressure gradient remains for Friday so that will mean more
gusty NW flow. At the surface, the low will be moving near
Newfoundland while the high will be moving into the Great Lakes and
into the west of the Appalachians.

NW flow continues so dry conditions will remain. Still expecting
abundant clouds though, so will side with a blend for high
temperatures including the previous forecast.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
NW flow aloft Friday night. With no shortwave embedded in the flow
progged to impact the region, have continued with the dry forecast.
Lows Friday night should be around 5-10 degrees below normal.

A couple of northern stream 700-500 hPa shortwaves push through the
area Saturday and Saturday night as the rotate around the base of a
closed low over the Canadian Maritimes. With relative dry low levels
and downsloping boundary layer flow, the shortwaves should pass
through dry. Highs on Saturday and low Saturday night should be
around 5-10 degrees below normal.

Deep layered ridging then begins to builds in Sunday and continues
to ridge over the area through Tuesday. Subsidence associated with
the ridge should keep things dry and relatively (if not totally)
cloud free during this time frame. Highs Sunday-Tuesday run a few
degrees below normal and lows during this time frame run 5-10
degrees below normal.

Noting that 1) the GFS has a known progressive bias in the long term
and 2) that the upper level pattern features closed lows and fairly
sharp ridges - both of which support a less progressive pattern -
favor the slower lifting of the ridge axis to the NE and arrival of
the next system in the ECMWF/CMC Global than the more progressive GFS
handling of both features. The forecast Tuesday night-Wednesday is
based on a blend of the ECMWF/CMC Global as a result.

Tuesday night should be dry as the deep layered ridge axis lifts to
the northeast. Most of Wednesday should probably be dry as well, but
to keep things simple, given the inherent uncertainty this far out,
have run chance pops the entire period for some warm advection
induced rains. Lows Tuesday night should be near to slightly above
normal and highs on Wednesday a few degrees below normal.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
Low pressure passes to the south today.

Generally VFR/MVFR today. -SHRA returns around noon. Conditions
become VFR late this afternoon/early evening with -shra ending.
NE-N winds around 10 kt bcmg NW and increasing to 10-20kt with
gusts 20-30kt this afternoon. Gusts continue into evening.

     NY Metro Enhanced Aviation Weather Support...

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

KJFK TAF Comments: Changing flight categories expected today.
Winds prevail north of 310 magnetic this afternoon into early
evening.

The afternoon KJFK haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KLGA TAF Comments: Changing flight categories expected today.
Winds prevail north of 310 magnetic this afternoon into early
evening.

The afternoon KLGA haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KEWR TAF Comments: Changing flight categories expected today.
Winds prevail north of 310 magnetic this afternoon into early
evening.

The afternoon KEWR haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KTEB TAF Comments: Changing flight categories expected today.
Winds prevail north of 310 magnetic this afternoon into early
evening.

KHPN TAF Comments: Changing flight categories expected today.

KISP TAF Comments: Changing flight categories expected today.

.OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY...
.Friday...VFR. NW winds G20-30KT.
.Saturday-Monday...VFR.

&&

.MARINE...
Sub-SCA conditions will be in place today, but winds and seas
will begin increasing. SCA thresholds are forecast to be met
across the waters tonight through Friday morning with the ocean
east of Moriches Inlet likely getting SCA conditions tonight through
all of the day Friday.

A relatively strong pressure gradient over the region Friday night,
should allow for gusts to around 25 kt to persist over the coastal
ocean zones and gusts to around 20 kt on the non-ocean zones.

The pressure gradient begins to slacken on Saturday, with all waters
falling to below Small Craft Advisory thresholds by Saturday
morning. Winds Saturday-Monday night will be limited to 10 kt or
less on the non-ocean waters. The coastal ocean zones will be
similarly limited Saturday-Monday night, except for winds up to 15 kt
are probable Saturday morning.

&&

.HYDROLOGY...
Less than a half inch of rain expected through this evening with
dry conditions for late tonight through Friday. No hydrologic
impacts expected.

It should be dry Friday night-Tuesday night, with light rain
expected Wednesday. No significant hydrologic impacts are expected
Friday night-Wednesday as a result.

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off
the air.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory from 6 PM this evening to noon EDT Friday
     for ANZ330-335-338-340-345-353-355.
     Small Craft Advisory from 6 PM this evening to 6 PM EDT Friday
     for ANZ350.

&&

$$

UPDATE...DW
AVIATION...BC/JC


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