Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service New York New York
1255 am EST Wed Dec 11 2019
a weak wave of low pressure moves offshore this morning. Arctic
high pressure then builds across the region, punctuated only
briefly by a secondary cold front that will pass to the north
Wednesday night. The high shifts offshore Thursday night with
low pressure approaching from the south Friday. This low passes
through on Saturday with low pressure building back in on
Near term /until 6 am this morning/...
the cold front is offshore early this morning with temperatures
steadily dropping. Rain is beginning to mix with snow across
western Orange County and this transition should move to the
coast through 09z.
The thinking with regards to snow accumulations appears on
track overall. Regional radar mosaic shows a wealth of
precipitation all the way down into Maryland and Virginia ahead of 500
mb shortwave energy. This precip is blossoming to the north-northeast
associated with a 170-180 kt jet streak to the northwest. Large scale
lift will only increase through the early morning hours as the
thermal profiles cool.
Have been monitoring the trends in the last several runs of the
hrrr and the model seems to be handling the current situation
fairly well. Thinking its projection of several bands of snow
within a larger precip shield early this morning looks on
target. The snow will be quickest to end across the lower Hudson
Valley and interior NE NJ, but will linger through the morning
commute across NYC, Long Island and southern Connecticut. A wet
snow is expected, but with temperatures dropping to the low 30s
as the snow intensity increases, slick conditions should develop
on roads as well. Most of the snow accumulation should be on
grassy surfaces, but within moderate to heavy snow bands roads
could become snow covered despite a warmer ground temperature.
Hrrr soundings indicate significant lift in a saturated
dendritic growth zone especially across Long Island and southern
Connecticut. This is the area where higher snow amounts look
Snowfall amounts continue to be less north and west of NYC with
around an inch, but some locations could even see slightly
higher amounts here. Have issued an Special Weather Statement to account for potential
travel issues in the snow. As temperatures drop below freezing,
icy roads could be an issue even if snow does not accumulate
efficiently. 1-2 inches still looks likely in the advisory area,
but there could be higher amounts closer to 3 inches across Long
Island and southern Connecticut in the banding mentioned above.
The snow will also linger well into the morning further east.
One concern early this morning is the western extent of the snow
during the morning commute. Will need to monitor radar and high
res model trends through the morning as strong jet streaks to
our northwest such as the one in this case could help keep snow going a
bit longer than forecast.
Short term /6 am this morning through 6 PM Thursday/...
snow gradually comes to an end from west to east by late
morning. Given the recent moisture and a strengthening
subsidence inversion, some cloud cover may linger across the
area through the afternoon, before dry advection gradually leads
to its dissipation. Expect temperatures to be below normal in
the mid to upper 30s, some 20 degrees colder than Tuesday.
Arctic high pressure then strengthens and builds to the west
while a secondary cold front passes to the north Wednesday
night. As a result, winds and the subsequent cold advection will
strengthen into the overnight, with temperatures falling into
the teens to mid 20s.
Long term /Thursday night through Tuesday/...
high pressure ridge shifts closer to the region on Thursday, moves
through by late in the day, and then offshore through Friday. Dry
weather this period with high temperatures below normal Thursday.
Temperatures level out or even rise slightly Thursday night with an
increase in clouds and light onshore flow. Some models Show Low precipitation
chances by the end of the morning rush on Friday from around the
city to points north and west. Should some precipitation sneak in by this
time, there could be some light freezing rain primarily well north
and west of the city during the first half of Friday morning. Mid
levels are forecast to be dry, so ice nucleation/snow growth does
not appear to be likely. Rain chances then increase some more
through the rest of the forecast area Friday afternoon with
temperatures moderating to near 50 by the end of the day along the
coast, and 40s for most other locations.
Low pressure to the south moves closer Friday night is progged to
pass over or nearby the forecast area Saturday morning. Rain is
expected Friday night and Saturday and could be briefly heavy at
times, but primarily moderate in intensity.
High pressure begins to build back in during Saturday night with
still a chance of rain showers primarily northwest of the city, and
maybe even some snow mixing in over parts of Orange County. Sunday
should be dry, and the high pressure system's ridge passing through
should keep US dry through Monday. Another low pressure system then
approaches from the Ohio Valley Monday night with increasing chances
of rain or mixed precipitation into Tuesday.
Aviation /06z Wednesday through Sunday/...
a cold front will move across the area tonight. High pressure
builds into the region on Wednesday.
Generally VFR conditions to start the taf period will quickly
give way to MVFR and eventually IFR as steadier precipitation
moves back into the region this evening. While precipitation
initially starts as rain, it will change to a rain/snow mix and
eventually to all snow from northwest to southeast. This changeover is
expected to occur between 03-06z for the lower Hudson Valley
terminals, 05-08z for the Connecticut terminals, and 06-09z for
the NYC and Long Island terminals. Snow then continues into
Wednesday morning, ending from northwest to southeast between 11-16z. A brief
period of moderate to locally heavy snowfall is possible in the
morning if any banding sets up. Runway accumulations will
generally range from 1-2 inches, with slightly higher
accumulations possible for some Long Island and southeast
Connecticut terminals. The timing of changes in precipitation
type and the start/end time of snow could be off by 1-2 hours.
Conditions improve to VFR Wednesday afternoon once the snow
Winds will continue to shift to the northwest tonight at 10-12 kt. A
few gusts to 25-30 kt are possible immediately ahead of the
front, but expect any gustiness to be short-lived. Winds then
diminish to 5-10 kt by Wednesday morning before shifting back
to the west and increasing in speed towards the end of the taf
period. A few gusts to 20-25 kt are possible late Wednesday
afternoon, primarily at the city terminals.
Outlook for 00z Thursday through Sunday...
Wednesday night...VFR. Gusty west-northwest winds possible.
Friday and Friday night...VFR on Friday, then MVFR possible in
developing rain Friday night.
Saturday...IFR in rain. Low level wind shear possible.
a weak wave of low pressure passes offshore this morning.
Arctic high pressure then builds across the region, punctuated
only briefly by a secondary cold front that will pass to the
north Wednesday night. The secondary cold front may allow winds
to surge to above Small Craft Advisory levels, with a few gusts close to gale-
force possible on the ocean waters Wednesday night. Otherwise,
winds gusts will generally remain below 25 kt into the mid week.
Seas remain elevated at this time, but will very slowly subside
into Wednesday with a brief lull in winds, before building
again Wednesday night following the secondary frontal passage.
Winds and seas diminish on Thursday as a ridge of high pressure
approaches the waters. Sub-advisory conditions expected by Thursday
afternoon and lasting through Friday afternoon as the ridge shifts
through and moves offshore. Winds and seas then increase Friday
night ahead of low pressure, which is expected to pass through or
nearby during Saturday morning. Small Craft Advisory conds are probable on the ocean,
and possible on the other waters depending on the exact track of the
storm. Winds and seas remain elevated on Sunday behind the storm
with the potential of gale force gusts at least on the ocean.
no hydrologic issues are expected with precipitation through
1-2 inches of rainfall with locally higher amounts are anticipated
from late Friday/Friday night through Saturday. Minor nuisance
flooding will be possible with this event.
there will be a chance of coastal flooding with the high tide cycle
during Saturday morning. This will be due to onshore winds with an
approaching storm combined with relatively high astronomical tides
due to a nearly full moon. Minor coastal flooding will be possible
primarily along the South Shore back bays of Long Island, where even
moderate coastal flooding is a possibility at least along the Nassau
County bays. Minor flooding will also be possible along New York Harbor
and parts of western Long Island Sound. Confidence is not high at
this point as the event is still a few days away, and shifts in
storm's track and/or timing would change the flooding potential.
NYC National oceanic and atmospheric administration weather radio station kwo35 (162.55 mhz) is still
operating at reduced power.
CT...Winter Weather Advisory until 11 am EST this morning for
New York...Winter Weather Advisory until 11 am EST this morning for
New Jersey...Winter Weather Advisory until 11 am EST this morning for
Marine...Small Craft Advisory until 6 PM EST this evening for anz350-