Scientific Forecaster Discussion
fxus61 kokx 130039
Area forecast discussion
National Weather Service New York New York
739 PM EST Thu Dec 12 2019
high pressure moves east tonight. Low pressure approaches from the
south Friday and passes through on Saturday. High pressure
builds in Sunday into Monday. Another storm then impacts the
area for late Monday night into much of Tuesday. High pressure
then builds in Wednesday through Friday.
Near term /until 6 am Friday morning/...
very minor adjustments this update with temperatures, dewpoints,
and sky cover, otherwise forecast remains on track.
Upper level trough begins to take shape east of The Rockies tonight,
with surface high moving east of the area.
High clouds move in this evening, but not enough to prevent
temperatures to fall into the 20s as winds remain light. As winds
begin to pick up ever so slightly from the se, increasing low level
moisture and thus additional clouds will result in temperatures to
hold steady, then rise toward morning.
Do not expect any precipitation tonight, just chilly temps in the
evening rising overnight, and increasing clouds.
Short term /6 am Friday morning through Saturday/...
digging upper trough will result in sfc low development over the southeast
states. The trough will then steer this low up the mid Atlantic
Friday night, passing somewhere nearby on Saturday.
A coastal front also develops, approaches Friday night, and passes
across the coastal plain Saturday.
With increasing low level moisture, and weak isentropic and
topography driven lift, light rain or drizzle should develop over
parts of the area Friday morning, and will become more widespread
later in the day as overall lift increases with the approaching
trough, and sfc front. Careful analysis of all available data,
including high resolution model data shows chilly temps rising
through the day, with some interior locations in the lower Hudson
Valley, and interior southern CT possibly cold enough for some fzdz
in the morning. However, all of this guidance shows warming sfc
temps above freezing, even where some damming occurs across the CT
valley Friday afternoon. Once the bulk of the rain moves in late
day/Friday night, all rain is expected. The widespread rain will
taper off and lower in coverage during the day Saturday as best lift
Temps warm through the day Friday, and remain mild or even rise more
Friday night as the front approaches.
Long term /Saturday night through Thursday/...
to begin the long term period the upper level trough axis will
swing through with good global model consensus with the time
around 6z Sunday. Look for more distinct clearing to take place
around or just after 6z from west to east across the region as
cold and dry advection takes places. With a colder dome aloft
approaching into late Saturday night and especially on Sunday
look for lapse rates to steepen. Mixing will increase, but not
sure how much above 5 kft based on BUFKIT forecast soundings. It
may not matter all that much as even 2 to 3 kft winds will be
rather strong out of the west and northwest. So widespread 30 to
35 kt gusts seem likely, especially towards Sunday morning.
Therefore Sunday will feature gusty winds with temperatures
slightly cooler, but still actually above normal. The more
noticeable cold air will arrive into Monday morning as
temperatures return closer to normal levels and will actually
most likely be a touch below normal into Monday.
The next system will then quickly approach for Monday evening
and Monday night and impact the region through most of Tuesday.
Another fairly quick moving shortwave in the Pacific branch of
the jet stream will approach from the west. The global guidance
has differences basically with how much ridging gets into the
area from the SW Atlantic with the GFS based guidance more
aggressive with this ridging along and just off the eastern
Seaboard. The European model (ecmwf) and Gem are less amplified with the
downstream ridging which will factor into p-type for the
beginning of this next system. There may be enough evaporating
cooling at the onset to even have the coast begin briefly as
mostly snow. A warm tongue will rush in quickly at the mid
levels and even at the surface later Monday night into Tuesday
morning. So went with a general snow to mix, or snow to mix to
rain north and west, with a brief snow or snow rain mix changing
to rain for the city and the coast. Northwest sections may even end as
some snow showers as the system pulls away late Tuesday into
Tuesday evening. It does not look like a major event, but with
ptype issues for at least northwestern sections this system will
have to watched over subsequent forecast cycles because a track
further south and east would introduce more mixed ptype for a
longer period of time further south and east. For now the
feeling is that at least enough warming will take place, even
for most northwestern sections for the majority of the precip to
be in the liquid form.
Clearing may then be a bit slow during Tuesday night, with more
in the way of clearing after the upper level trough axis swings
through during the day on Wednesday. High pressure will begin to
build in later Wednesday and into the latter part of the week.
This period will feature dry and colder weather. The source
region for high pressure later next week will be from a colder
source region, therefore temperatures during late next week will
be noticeably colder as temperatures fall below normal.
Aviation /00z Friday through Tuesday/...
high pressure will continue to retreat offshore through Friday,
while an area of low pressure works up the eastern Seaboard.
VFR to start tonight with MVFR ceilings developing late across
the NYC and lower Hudson Valley terminals. To the east, VFR
conditions may hold on through mid to late morning Friday.
Conditions will then gradually deteriorate to IFR with
increasing chances of rain from late afternoon into early
evening. There is a fair amount of uncertainty in the timing of
the category changes Friday into Friday night. Preference at
this time was to take a middle Road approach with the guidance.
Note if precip starts early enough, there could be some light
freezing rain or drizzle towards khpn and kswf but probabilities
for this are too low so this is not in tafs.
Light east/southeast winds tonight will gradually back through the day at
5 to 10 kt. Low level wind shear possible late in the day.
Outlook for 00z Saturday through Tuesday...
Friday night...mainly IFR in rain. Low level wind shear possible.
Saturday...IFR in rain. Low level wind shear possible early.
Saturday night...scattered showers, mainly early. Improving to
VFR with west winds increasing to 10 to 15kt g20-30kt.
Sunday...VFR. West winds 10-20kt gusts 25-35kt.
Sunday night-Monday...VFR. Some west wind gusts to 20 kt
Monday night-Tuesday...MVFR to IFR possible. Chance of snow
for inland terminals changing to a wintry mix and then to rain.
Chance of mainly rain for coastal terminals, with a period of
snow or a wintry mix at the start early Monday night.
winds turn to the southeast tonight as high pressure moves east. The
pressure gradient tightens as the low moves east and low pressure
approaches Friday and Friday night. Small Craft Advisory winds are possible later
Friday across the ocean waters, with gusty easterly winds Friday
night ahead of a coastal front and low pressure. Will issue Small Craft Advisory for
only the ocean waters at this time for late Friday and through
Friday night. Seas build to 5 ft or greater as well during this time
frame. Rough seas continue Saturday as the low and front pass north.
Small craft conditions will develop for the non-ocean coastal waters
during Saturday night with seas already elevated out on the ocean.
Small craft conditions are expected across all the waters by late
Saturday night, with the potential for gale force gusts developing
out on the ocean waters, especially the eastern coastal waters. The
strengthening winds will be due to an intensifying pressure gradient
on the back side of departing low pressure and building high
pressure off to the west. On Sunday gale force gusts are looking
more likely for all of the ocean waters, with small craft conditions
for the remaining coastal waters. The winds will then diminish into
Sunday night along with high seas out on the ocean starting to come
down. By Monday seas and winds should diminish enough that sub Small Craft Advisory
conditions will prevail. By late Monday night seas will begin to
build out on the ocean waters, with small craft conditions likely
out on the ocean with small craft wind gusts. Seas will climb to
high levels out on the ocean, especially for the eastern ocean
waters late Monday night into Tuesday.
1.00 to 1.50 inches of rainfall with locally higher amounts are
anticipated from late Friday through Saturday. Minor nuisance
flooding will be possible with this event, especially Friday night
when the bulk of the rain falls.
No hydrologic impacts in the long term period.
there will be a chance of coastal flooding with the high tide cycle
during Saturday morning (departures of 1 to 2 ft are needed to reach
minor benchmarks). 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 remains rather
low on details due to possible shifts in storm track and/or
NYC National oceanic and atmospheric administration weather radio station kwo35 (162.55 mhz) is still
operating at reduced power.
Marine...Small Craft Advisory from 4 PM Friday to 6 am EST Saturday for
near term...precipitable water
short term...precipitable water