Area Forecast Discussion
Issued by NWS Upton, NY

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607
FXUS61 KOKX 240450
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1150 PM EST Fri Feb 23 2018

.SYNOPSIS...
A warm front moves across overnight, followed by a cold front
early Saturday. Another low pressure system approaches for
Saturday, with its warm front moving towards the region Saturday
night. A low develops along it and this moves across Sunday.
High pressure builds from the Midwest Sunday night and remains
in control through the middle of next week. A frontal system
then approaches for the end of the week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
The fcst is generally on track, although the warm front is
still a good distance from the area and will be slower to
arrive than previously fcst. The front will be moving across
overnight as winds switch to a more southwest to west flow.

Expecting some fog across the region for at least the first
half of tonight before that more westerly flow develops. The 00z
OKX sounding indicated a saturated airmass up to about 4500 ft.
This deep moist layer is likely limiting the density of the
fog. Still, with winds slackening off significantly there could
be some pockets of dense fog to develop. Drier conditions on
that more westerly flow can be expected for the remainder of the
night.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
This weekend features a strengthening upper level jet from Baja
California extending northeast through the Great Lakes and Northern
New England. The jet itself approaches closer to the region on
Sunday, with the local region getting close to the right front quad
of the upper level jet.

The mid levels convey a ridge moving in with its axis oriented
southeast to northwest with a nearly steady height tendency Saturday
into Saturday evening. A shortwave from the Southwest US will travel
and pivot into the Great Lakes Saturday night into Sunday morning.
Then for Sunday, this shortwave further pivots into Ontario.

At the surface, another low pressure system developing in the South
Central US will have its associated warm front approaching. The day
starts out dry but there will be increasing chances of rain in the
afternoon from southwest to northeast as this warm front approaches
and with some forecast increase in isentropic lift aloft. Used a
blend of MAV and ECS MOS for high temperatures, getting well into
the 50s as a light northwest flow acts as a downslope for adiabatic
warming from higher temperatures aloft.

Saturday night into Sunday will be the bulk of the rainfall. The
warm front will be approaching and with the parent low heading into
the Western Great Lakes and deepening, an increasing easterly flow
will take place. This will load the atmosphere with more moisture as
layer precipitable waters are forecast to increase to 1.1 to 1.4
inches. This will facilitate at times moderate to perhaps heavy
rain.

For temperatures, Saturday used the relatively warmer blend of
MAV and ECS MOS as well as NAM12 2 meter temperatures, mid 30s to
near 40. For Sunday, with rain much of the day used GMOS with 2
meter temperatures of GFS and ECMWF, showing a range from the low
40s to near 50.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
The general North American pattern of troughing in the west and
ridging east of the Rockies looks to continue into next week.
The upper pattern starts to diverge mid to late week next week
as a closed low pres system moves onshore in California and
continues into the Plains. The EC is much slower than the GFS,
but has support from the CMC, therefore this idea was preferred,
but there is low confidence in the details late next week since
there is also large spread in the GEFS and ECENS.

In terms of sensible weather, dry weather returns Sun night as
low pres departs and high pres builds from the Midwest. The high
will remain in control through the middle of next week,
resulting in a continuation of above normal temperatures. Rain
chances will begin to increase Wed night as a WAA pattern ensues,
although due to the aforementioned uncertainty in the upper
pattern, rain could very well hold off until Thu night. Have
scaled back on the previous forecasts PoPs a bit in light of
the 12z data and the large amount of uncertainty. At this time,
atmospheric profiles suggest pcpn starts as rain, with colder
air aloft working in late Thu night/Fri. This may be enough for
a brief period of a wintry mix across locations N of NYC.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
High pressure builds to the north through Saturday as a frontal
boundary stalls south of the area. Another area of low pressure
will approach from the west Saturday into Saturday night.

Conditions are predominantly IFR-LIFR in stratus and fog
tonight, but gradual improvement is anticipated overnight as
high pressure and drier air move back in from the north.
VFR conditions will then prevail for most of Saturday until
evening, when rain begins to move back into the area from the
west.

Winds diminish tonight, possibly becoming light and variable
before becoming NW Saturday morning. Winds then shift to the NE
Saturday evening.

.OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY...
.Saturday Night-Sunday...MVFR/IFR in rain. E-SE wind 10-15kt,
G20-25kt.
.Sunday night-Wednesday...VFR.

&&

.MARINE...
With a decreasing pressure gradient, winds and seas are
expected to continue to decrease as well into tonight. The more
westerly flow late tonight will briefly increase winds but wind
gusts will remain just below SCA criteria. With further
offshore flow, expect sub SCA conditions to continue.

Sub-SCA conditions are expected to continue through Saturday
evening. Easterly flow then strengthens into Saturday night
between the departing high and an approaching area of low
pressure, leading to SCA conditions with the possibility of
gales as well on the ocean for Sunday morning.

Hazardous ocean seas are expected to continue into Mon, with sub-
advsy conds thereafter with high pressure building from the
west.

&&

.HYDROLOGY...
Around 0.75 to 1.25 inches of rain will be possible late
Saturday into Sunday. There may be locally higher amounts
especially in any areas of orographic lift with the higher
terrain. Ponding of water and minor nuisance flooding could be
localized for Sunday.

&&

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

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

&&

$$
SYNOPSIS...24/JM
NEAR TERM...JMC/JM
SHORT TERM...JM
LONG TERM...24
AVIATION...MD/19
MARINE...24/JM
HYDROLOGY...24/JM
EQUIPMENT...



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