Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 190859
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
459 AM EDT Thu Apr 19 2018

.SYNOPSIS...
Low pressure tracks to south of Long Island this morning and
will then move to the southeast of Cape Cod this afternoon. The
deepening low then quickly exits into the Canadian Maritimes
tonight through Friday. 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/...
The main upper level jet will be south of the region. A
persistent upper level low will remain in the Northeast. The mid
levels convey a flattened mid level ridge moving east of the
region with an approaching shortwave trough. At the surface, a
low will be moving to south of Long Island this morning and then
this low will be tracking to southeast of Cape Cod.

Low level warm air advection has been occurring with some
isentropic lift as well. This will be a setup for overrunning
rain that will be main weather theme of the day. Going into this
morning, higher terrain across the interior could have the
precipitation as a rain/snow mix or even some snow. Little to no
snow accumulation is expected, if anyplace gets any
accumulation, it would be the higher terrain where temperatures
will be slightly below freezing.

Expecting a damp cool day as temperatures will not rise much
from early morning values.

Continuous rain expected on a light northerly flow to start but that
flow will increase towards mid to late afternoon as pressure
gradient becomes tighter between the low and strong high pressure
still well out west into the Central Plains.

Expecting cooler than normal temperature with the northerly flow and
rain through the day. Used the cooler MET guidance for highs.
Increased one degree along the coast for highs.

&&

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

For Thursday night:

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 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 /09Z THURSDAY THROUGH MONDAY/...
Low pressure passes to the south today.

VFR bcmg MVFR to locally IFR after around 12z. RA/-SHRA through
around 12z, then a break until around noon when more rain
probably moves in. VFR returns late aftn.

...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: Timing of flight category changes may be off by 1-
2 hours. CHC IFR cigs within a couple hours either side of noon.
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: Timing of flight category changes may be off by 1-
2 hours. CHC IFR cigs within a couple hours either side of noon.
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: Timing of flight category changes may be off by 1-
2 hours. CHC IFR cigs within a couple hours either side of noon.
Winds prevail north of 310 magnetic this afternoon but could be
south of it at times early evening.

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

KTEB TAF Comments: Timing of flight category changes may be off by 1-
2 hours. CHC IFR cigs within a couple hours either side of noon.

KHPN TAF Comments: Timing of flight category changes may be off by 1-
2 hours. CHC IFR cigs do not occur.

KISP TAF Comments: Timing of flight category changes may be off by 1-
2 hours.

.OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY...
Thursday night-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.

&&

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


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