Scientific Forecaster Discussion
fxus61 kokx 092347
Area forecast discussion
National Weather Service New York New York
647 PM EST Mon Dec 9 2019
a cold front will approach tonight into Tuesday and will move
across late Tuesday into Tuesday night. Weak low pressure
develops along the front offshore slowing down its eastward
progress Wednesday. Another low pressure trough approaches
Wednesday before strong Arctic high pressure builds into the
region Wednesday night through Thursday. The high moves off the
northeast coast Thursday night. A low pressure system
approaches from the southwest Friday and moves through the area
Saturday and Saturday night. High pressure builds Sunday and
Near term /until 6 am Tuesday morning/...
a warm front north of the area will weaken and eventually
dissipate tonight. The region is in a larger warm sector of a
low pressure system of which the parent low will be moving into
southeast Canada. The associated cold front will be approaching
the region through tonight.
Aloft, the mid levels show nearly a steady height tendency with
a strong shortwave pivoting into the Great Lakes.
Rain continues this evening, moderate to heavy at times,
before becoming more intermittent and lightening overnight into
Tuesday morning. This evening, the rain could bring down some
higher winds, but keeping gusts below 35 mph for the most part
as inversion aloft limits mixing. Without any surface
instability and elevated instability as diagnosed from forecast
showalter indices showing slightly positive values, removed
thunder from forecast.
Temperatures will not drop too much tonight, making for minimal
diurnal temperature trends. Forecast lows are from the mid 40s
to lower 50s using a consensus of model guidance.
Short term /6 am Tuesday morning through Wednesday/...
the short term will feature the rainfall ahead of and along the
cold front Tuesday into Tuesday evening as well as the mixing
with and changing to snow behind the cold front later Tuesday
night into Wednesday.
For this timeframe, used mostly a consensus of raw model
temperatures with some slight adjustments downward for Tuesday
night and Wednesday when colder air will be advecting into the
region on more of a northwest flow.
In the upper levels, a jet streak will be approaching and will
move in with its right rear quad by Wednesday morning, before
moving farther northeast. Mid level shortwave trough will be
approaching Tuesday and then move across the region Tuesday
night into Wednesday with the most positive vorticity advection
staying north of the region. The most forcing for lift will be
late Tuesday night into Wednesday.
At the surface, the cold front approaches Tuesday and moves
across late Tuesday afternoon into Tuesday evening. Rain
continues through the day which could again be moderate at
times. Precipitation lingers behind the cold front for Tuesday
night into Wednesday and models have been pretty consistent
showing potential for 1 to 3 inches of snow for much of the
area, 3 to 4 inches across the interior, which is reflected in
the current forecast. Initially, the changeover from rain to
snow will be limited with accumulation especially if it is light
as ground temperatures will be above freezing. The snow
accumulation occurs Wednesday morning when much of the region is
at freezing or below. Some slight rise in temperatures expected
during the day, low to mid 30s.
While the amounts of snow forecast are 1 to 4 inches, the timing
puts this during the Wednesday morning commute, making for
potentially hazardous travel conditions due to slippery surfaces
and reduced visibilities.
Weather becomes drier Wednesday afternoon into Wednesday evening
with a slow decrease in clouds as the shortwave trough starts to
lift north of the region.
Long term /Wednesday night through Monday/...
Wednesday night through Thursday night the guidance is in good
agreement with Arctic high pressure building over the region and
then departing off the northeast coast. Well below normal
temperatures are expected Wednesday night and Thursday. The
upper flow becomes nearly zonal through Thursday night.
Differences then develop with the next shortwaves impacting the
area Friday into Saturday night. Split flow is expected to
develop and the timing, and strength, of the northern and
southern stream shortwaves differs. Regardless, the southern
stream wave remains dominant, with warm advection increasing
ahead of a developing warm front. The best chances at this time
for snow and/or a rain snow mix will be across the interior
Friday morning. Then timing of the warm up will determine the
changeover to rain. Along the coast rain is expected. A lot of
uncertainty remains with the strength of the northern stream
shortwave and the interaction with the southern stream wave
later Saturday into Sunday. The GFS is much farther to the north
and deeper than the European model (ecmwf) with the northern stream.
High pressure and colder weather returns Sunday into Monday.
Aviation /00z Tuesday through Saturday/...
a cold front over the Midwest will slowly approach the area through
IFR or lower conditions expected through the overnight hours in
rain. The bulk of the rain should come to an end between 05-07z,
but drizzle could linger through daybreak. Showers then return
ahead of the approaching front Tuesday morning, with another
round of steady rain expected Tuesday afternoon. Some
improvement is possible Tuesday afternoon, although conditions
are still expected to remain MVFR at best.
Visibility through the overnight hours may be lower than
indicated by the tafs, especially once the steadiest
precipitation comes to an end. Too much uncertainty in this
scenario remains to include in the tafs at this time.
S winds 10-15 kt expected tonight, with gusts up to 25 kt
possible, primarily at city and coastal terminals. Low level wind shear at all
terminals through tonight. Winds shift to the SW at around 10
kt during the day on Tuesday, then west-northwest by the end of the taf
Outlook for 00z Wednesday through Saturday...
Tuesday night...winds shift to the northwest behind the cold front.
Rain transitions to snow from northwest to southeast.
Wednesday...IFR or lower possible in snow in the morning,
improving to VFR late.
Friday...MVFR possible in developing rain.
Friday night-Saturday...IFR in rain or a wintry mix. Low level wind shear
no changes to winds and seas at this time.
Gale Warning in effect for all ocean zones through tonight. Small Craft Advisory
remains in effect for non-ocean waters through tonight. For
Tuesday, Small Craft Advisory conditions remain on the ocean and continue through
Tuesday night. Small Craft Advisory remains on much of the ocean Wednesday
before dropping below Small Craft Advisory mid to late Wednesday afternoon west
of Moriches Inlet.
Small Craft Advisory in effect for all waters. Main push of stronger winds to
the east today, and gusts in S-SW flow getting close but not
quite to 35 kt except on the ocean east of Moriches Inlet this
afternoon. Gale Warning starts on the ocean east of Moriches
Inlet this afternoon. Rest of ocean, Gale Warning starts
tonight. Gales remain on ocean until Tuesday morning and Small Craft Advisory
remains on non-ocean waters until Tuesday morning. Gales subside
Tuesday with Small Craft Advisory remaining on the ocean. Tuesday expected to be
below Small Craft Advisory on non-ocean waters.
Increasing, and gusty, northwest flow develops Wednesday night
behind departing low pressure. Marginal Small Craft Advisory conditions are
expected to develop on the ocean waters Wednesday night and
continue into Thursday morning.
With high pressure moving across the waters Thursday and
departing Friday sub advisory conditions are expected. Then east
to southeast winds will increase ahead of the next low pressure
system moving in from the southwest Friday night. Once again,
marginal Small Craft Advisory wind gusts are expected on the ocean waters Friday
night through most of Saturday, while ocean seas will build
significantly Friday night into Saturday.
long duration rainfall event continues through Tuesday evening
before mixing with and changing over to snowfall late Tuesday
night into Wednesday. Total liquid equivalent remaining is
between 1 to 2 inches.
Nuisance/poor drainage flooding may occur tonight when the
heaviest rain falls but otherwise no other flooding is expected.
The next significant rain of up to an inch is expected Friday night
through Saturday. Timing and rainfall amounts may change, so
hydrologic impacts are uncertain at this time.
NYC National oceanic and atmospheric administration weather radio station kwo35 (162.55 mhz) is still
operating at reduced power.
Marine...Small Craft Advisory until 6 am EST Tuesday for anz330-335-338-
Gale Warning until 6 am EST Tuesday for anz350-353-355.