Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1025 PM EST Thursday Dec 5 2013
a cold front crosses the region tonight. Low pressure rides the
stalled front Friday night with high pressure building in for the
weekend. Low pressure returns Sunday night and impacts the
northeast through the first half of next week. High pressure
builds in for the second half.
Near term /until 6 am Friday morning/...
a warm front over or just north of the region...should gradually
push north overnight ahead of a cold frontal passage late tonight
into early Friday morning.
An unseasonably mild and moist airmass and light winds conducive
to areas of dense fog development overnight. Visibilities have
been steadily going down this evening...and majority of guidance
indicates saturation all the way to the surface overnight. Increasing
winds aloft and rain shower activity may keep the dense fog from
being widespread...and will likely result in fluctuations in
visibility. But still enough of a hazard to maintain dense fog
Otherwise...increasing shower activity expected overnight from west
to east as weak shortwave energy approaches and cold front crosses
the region. Post-frontal rains will linger in the wake of the cold
frontal passage from northwest to southeast late tonight into Friday
morning...but improving visibilities are expected as northwest winds
bring in drier and cooler air.
Overnight lows will fall into the 40s to near 50. Followed a mav/met
Short term /6 am Friday morning through 6 PM Friday/...
the cold front stalls south of the area Friday morning. Behind
the frontal passage...winds turn northwesterly and cooler air
begins to filter in. Temperatures are expected to fall through the
day...with maximum temperatures occurring during the early morning
A wave of low pressure traveling along the front will result in
periods of light rain throughout much of the day on Friday.
Long term /Friday night through Thursday/...
many concerns with multiple systems impacting the region through the
coming week. Overall general agreement between the models of the
developing systems...but timing and strength will play into the type
of precipitation over the region.
First thing of concern. The cold front from during the day Friday
stalls just south of the region Friday night...with a surface low
forming and tracking along it...with the center passing just south
of the area. This is expected to bring widespread precipitation to the entire
region for the night...with fairly good agreement on the precipitation having
exited most of the region by 12z Sat...and the entire area by 15z.
The tricky part of the forecast is the type of precipitation. 12z GFS is a
bit more progressive in bringing in the colder air...though the NAM
and European model (ecmwf)...once the colder air moves in...drops the temperatures at a
quicker rate. For now...used the timing of the slightly slower
solution...keeping everything light to moderate rain for the first half
of the night...then transitioning to snow/freezing rain/sleet mix
over the Hudson River valley and interior CT. Soundings keep things
warm enough along the coast for mainly a rain event. Depending on
how quickly the precipitation exits...could see sleet mixing in as far south
as southern CT and the NYC metropolitan area early Sat morning with
lingering precipitation. At this time...keeping any freezing rain though to the north.
As the high builds in Sat...and the region remains under a near zonal
flow...expecting dry conditions to persist through at least Sunday
afternoon. As winds shift to a west-northwest-northwest flow...cold air advection will push
in cooler temperatures...with temperatures remaining below normal.
The next system of concern is a developing coastal low...which
eventually looks to phase with a passing system through the Great
Lakes region by late Monday. 12z models slightly slower in bringing
in the precipitation...so have tapered probability of precipitation back to only slight chance up to
NYC/Li for late Sun afternoon. Highest confidence with the timing of the
precipitation looks to be between 06z and 18z Monday...which unfortunately
corresponds to the coldest temperatures...and thus another round of mixed
wintry precipitation. With cooler temperatures in place to start sun...have a mix of
light rain/snow...with possible sleet even over interior regions sun
evening. As the heavier precipitation moves in...BUFKIT soundings bring areas
north and west of the city over to all snow with possible sleet while
keeping more of a rain/sleet mix at the coast. Right now...the
guidance hover overnight lows right around freezing for most of the
area...so confidence in type of precipitation right now is fairly low....with
refining most likely needed as we get closer and have a better
handle of the hourly overnight temperatures. However...the general onshore
flow will help in warm air advection which should push most...if not
all areas above freezing after 12z Monday...and thus switching all precipitation
over to all rain. The main trough aloft and associated energy pushes
through Tuesday...so could see lingering precipitation Monday night into Tuesday.
High pressure and zonal flow returns middle week...ushering in a much
colder airmass...with 850mb temperatures dropping to around -10 degrees by
Wednesday. Temperatures will remain well below normal then for the second half of
Aviation /03z Friday through Tuesday/...
the cold front moves across the region generally between 09z and
12z from northwest to southeast. Ahead of the front...light
southerly flow will help promote thick fog...low clouds and spotty
light drizzle with mainly LIFR to isolated vlifr conditions.
Likelihood of rain associated with the front increases overnight
into early Friday morning...with a gradual improvement in
conditions thereafter to MVFR/VFR as flow becomes more northerly.
IFR or below could last a few hours later than forecast Friday
morning. Conditions once again expected to lower to MVFR...isolated
IFR during the afternoon with another round of showers moving in.
Overall confidence is high for ceilings IFR or below tonight but lower
for visibilities which could fluctuate especially with the shower activity
along and behind the front. Overall confidence is moderate for
winds. Some uncertainty on how fast winds switch direction with
frontal passage which could be 1-2 hours off from forecast.
Outlook for 00z Saturday through Tuesday...
Friday night...MVFR/IFR with occasional -ra most terminals...ending as a
wintry mix for kswf. North wind.
Sat...becoming VFR early. Northwest wind 10-20kt.
Sun...VFR. Light wind.
Sun night...MVFR. Wintry mix > rain coast and CT. Snow > mixed precipitation
lower Hudson Valley.
Monday...IFR. Rain. Southeast wind 15-25kt becoming SW in afternoon.
Tuesday...VFR. West wind 15-25kt.
dense fog advisory continues for all of the area waters through
early Friday morning with visibilities falling to 1 nm or less.
Southerly winds will continue to increase ahead of an approaching
cold front. Have undercut previous forecast winds and sea a bit
with limited mixing. Occasional gusts to 25kt on the ocean waters
are possible late tonight...with marginal Small Craft Advisory ocean seas in
response. A Small Craft Advisory will remain up late tonight into
Friday. Winds and seas on the other waters will remain below
criteria...10-15kt gusts and 1-3ft seas.
Sub-Small Craft Advisory conditions expected through the weekend with high pressure
building in over the region. The developing low at the beginning of
next week will increase seas...with ocean waters reaching between
5-7 feet by Monday and gusts between 25 and 30 kts. The rest of the
waters will remain borderline with possible 25 kts gusts.
As high pressure returns by Wednesday...gusts will diminish...though seas
will be slightly slower in subsiding. All waters return to sub-Small Craft Advisory
conditions by Thursday.
precipitation through Saturday is expected to total around an
inch...with mostly rain expected.
Another storm system could bring a liquid equivalent precipitation
amount of a half inch to an inch from Sunday afternoon through
due to interference issues with the U.S. Coast Guard
emergency broadcast channel...the New York City National oceanic and atmospheric administration all hazards
weather radio station kwo35 remains out of service. The National
Weather Service is working with several U.S. Government agencies
to isolate and resolve this technical problem.
During this time...the transmitter may be returned to service
intermittently for use of the National oceanic and atmospheric administration all hazards weather radio
during potentially dangerous weather situations...for routine
weekly tests of the warning system...and to determine if the
interference issue has been resolved.
CT...dense fog advisory until 8 am EST Friday for ctz007>012.
Dense fog advisory until 5 am EST Friday for ctz005-006.
New York...dense fog advisory until 8 am EST Friday for nyz071-075-
Dense fog advisory until 5 am EST Friday for nyz067>070.
New Jersey...dense fog advisory until 5 am EST Friday for njz002-004-
Marine...dense fog advisory until 8 am EST Friday for anz330-335-338-
Small Craft Advisory until 6 PM EST Friday for anz350-353-355.