Area Forecast Discussion
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FXUS61 KOKX 100523 CCA
Area Forecast Discussion...CORRECTED
National Weather Service New York NY
1223 AM EST Sat Dec 10 2016
Weak high pressure builds in through Saturday night and then
offshore Sunday as low pressure over the Midwest tracks northeast.
The low will track across the Great Lakes Sunday night into
Monday, sending a warm front through the region. High pressure
will then briefly follow for Tuesday before another southern
branch low possibly impacts the area for the mid week period. An
arctic cold front then follows behind the system Thursday.
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Forecast remains on track. Pressure gradient has been lowering
with a resulting decrease in winds as high pressure continues to
build in from the west. Winds are expected to continue lowering
Low temperatures will be well below normal for this time of year,
20s for much of the region. Some upper teens in the outlying
areas. Wind chill values will be in the teens region-wide.
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
High pressure slowly builds into the region Saturday and Saturday
night. A weak shortwave and increasing low-mid level moisture could
trigger a few flurries mainly across the far NW portion of the
forecast area during the afternoon and evening hours. In general,
increasing afternoon clouds, then clouds diminish in the evening.
Temperatures through the short term are a blend of MAV/NAM MOS.
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Upper air pattern will feature an anomalously high amplitude ridge
over Alaska, which will allow the polar vortex to drop southward
into central and eastern Canada by midweek. This will open the
door for the coldest airmass of the season for the second half of
the week. Prior to the time, an active southern branch of the jet
will take several pieces of energy from a shearing upper low
dropping southward across western Canada and into the Pacific
Northwest quickly eastward.
At the surface, this will be reflected as area of low pressure that
will track northeast across The Great Lakes and into eastern Canada
Sunday night into Monday. A warm front will approach from the
southwest during the same time, passing through the region on
Monday. This type of fast flow with the low tracking to the
northwest of the area is typically not conducive for a significant
snowfall event, especially at this time of year due to a return
flow developing off of warmer waters. The high is also transient
in nature and builds quickly off the coast on Sunday. There are
though differences amongst the models in how quickly the cold air
erodes over the region Sunday night into Monday morning, with the
operational NAM the most aggressive, and the GFS and ECMWF cold
enough to support several inches of snowfall across the interior.
There is also another potential wrinkle with weak low pressure
forming to the south along the warm front Monday morning. This
could potentially hold in the cold air a bit longer. The exact
timing of when the boundary layer warms sufficiently for a
changeover to rain is critical and allows for a fair amount of
uncertainty in the forecast. For the time, have taken a multi
model ensemble approach, discounting the warm NAM, for a Ptype
forecast. This results in a quick changeover to rain at the coast
Sunday night, and then a northward transition across the Lower
Hudson Valley and interior southern Connecticut near daybreak. A
deviation by 1-2 hours with strong overrunning precipitation can
have a significant consequence. At this time,the forecast calls
for 2 to 4 inches across northern portions of the Lower Hudson
Valley and interior southern Connecticut, with less than an inch
at the immediate coast. The trailing cold front passes through in
the late afternoon/early evening Monday with conditions drying
from west to east. Total liquid equivalent looks to be 0.50 to
High pressure will briefly follow for Tuesday with temperatures
just below seasonable levels. Another piece of Pacific shortwave
energy races across the country. Global models vary with the
amplitude of this feature with the nearly zonal flow in the
southern branch of the polar jet. The amount of phasing with the
northern branch looks to be the difference. Due to the fast flow,
there is likely to be uncertainty in the magnitude of this system
the next several days. For now. will run with a chance of
rain/snow Wednesday afternoon/night. Arctic air then spills
southward on the backside of the system Thursday into Friday with
daytime highs possibly not getting above freezing with overnight
lows in the single digits to teens. These values are 15 to 20
degrees below normal. To make matters worse, strong NW winds will
follow for Thursday producing very cold wind chill values.
.AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
High pressure builds in from the west through the TAF period.
VFR. SCT-BKN CIGS 040-060 on Sat. Scattered snow showers/flurries
with brief reductions in cigs/vsby to mvfr/ifr Saturday afternoon.
Low prob/sparse coverage of a brief dusting.
Gusty WNW-NW winds at NYC Metro terminals decreasing
overnight. WNW winds with gusts to 20 kt re-developing Saturday
morning for all terminals. Winds diminish Sat Evening.
.OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY...
.Sunday...Mainly VFR. Chance of light rain/snow near coast and
chance snow inland late.
.Sunday night and Monday...IFR in light snow Sunday night,
changing to rain/snow mix from south to north early Monday morning
becoming plain rain along coast thereafter.
.Monday night...Rain/snow mix ends becoming VFR.
.Wednesday...MVFR or IFR possible in chance rain/snow mix.
The SCA remains for the eastern and ocean waters for overnight
with these conditions lowering Saturday morning. The Eastern Long
Island Bays and Sound are expected to drop below SCA by early
Saturday morning while the ocean is expected to subside below SCA
by late Saturday morning. Sub-SCA conditions are then expected
into Saturday afternoon and night.
There is a low chance for SCA conditions to develop Sunday night.
Seas on the ocean will build however on Monday as low pressure
passes through. Conditions improve on Tuesday with high pressure
building in. Low pressure may develop over the Atlantic during the
middle of the week, which could bring at least SCA conditions and
possibly gales Thursday behind an arctic cold front.
Up to an inch of rain and/or liquid equivalent is possible Sunday
New York City NOAA Weather Radio NWR transmitter KWO-35 is
experiencing intermittent outages.
MARINE...Small Craft Advisory until 10 AM EST this morning for ANZ350-
Small Craft Advisory until 6 AM EST early this morning for