Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/17/20
Area Forecast Discussion
National Weather Service Binghamton NY
936 PM EST Wed Dec 16 2020
A strong nor`easter will produce heavy, rapidly accumulating
snow tonight across central NY and northeast PA. The snow ends
Thursday morning with cool and quiet conditions Friday into
.NEAR TERM /THROUGH THURSDAY/...
10 pm update:
Latest mesoscale models have continued to nudge the heaviest
snow band a little further northward for the overnight hours.
This has resulted in amounts going up a few inches in the
Southern Tier and slightly lower across southern portions of NE
PA. The current snow band across the Northern Tier of PA should
lift into the Southern Tier of NY as well then stay in place
through the overnight. Top totals are still expected to be
around two feet.
7 pm update:
With the early evening update, we added Yates county to the
winter storm warning based on reports over 2 inches as of the
update time and the latest mesoscale models which are inching
north with the higher snowfall totals. The prospects of an
intense band are increasing for later this evening into the
overnight. Incorporated the latest NAM guidance which keeps the
best FGEN forcing just north of Scranton from Wyoming county
eastward to central Wayne county. Snowfall rates suggested by
the FGEN along with model QPF and snow ratios suggest snowfall
rates of 3 inches or so setting up over these locations. The
latest 22Z HRRR has this band located farther to the north into
the Southern Tier of NY so it is an evolving setup for later
tonight. Snowfall totals over two feet are likely to occur where
this intense snow band is located. We now show that stripe in
the latest snowfall map.
Another issue, is the potential for sleet mixture around the
Scranton area looks higher. A look at the KDIX CC line shows
the warm nose quickly advancing northward into the Lehigh Valley
as of 7pm. Although precipitation rates are high this update
leans more in the direction of the HRRR which which warms a
layer up between 800 and 900 mb just above freezing for a few
255 pm update...
Significant nor`easter remains the focus of attention for the
near term with heavy snowfall expected tonight across much of
the forecast area. Snowfall rates will be fairly impressive at
times tonight as well with the potential for thundersnow into
parts of ne PA. The ridge tops of the Poconos and the Catskills
may see some stronger gusts tonight too, which will create
blowing and drifting snow.
Rapidly deepening surface low off the the Carolina coast will
lift to the north tonight and become positioned off the NJ coast
by Thursday morning. As this occurs a positively tilted 500 mb
short wave will rotate across the Ohio Valley and mid Atlantic
region and combine with a coupled jet streak to provide robust
broad large scale lift. A fairly rich supply of moisture from
the Atlantic will get entrained into the surface low from the
east and be able to interact with a strengthening band of mid
level frontogenesis which is expected to set up over ern PA into
southern NY/nrn NJ late this evening and overnight.
The combination of this strong layer lifting mechanism and a
weak amount of elevated instability may provide enough
ingredients for a few strikes of thunder over the Poconos and
into the southern Catskills.
There is also a concern for gusty east/ne winds as the system
wraps up off the Jersey coast. Winds will pick up early this
evening and remain around 5 to 15 mph with gusts 20 mph through
the overnight. Some of the higher peaks of central NY and ne PA
may see gusts up to 30 mph. Areas that see stronger gusts may be
impacted by blowing and drifting snow. Visibilities may be
reduced to near zero at times.
Much of the region will likely see broad snowfall rates of 1/2
to 1 inch per hour. However, the deformation zone on the back
side of the system will be capable of producing snowfall rates
of 2 to 3 inches per hour at times with some isolated locations
of ne PA getting into a convective mode and potentially seeing
short bursts as high as 4 inches per hour.
The period of heaviest snow will be from around 6 pm to around
3 am. Total snow amounts will be roughly 18 to 24 inches in ne
PA portions of Southern Tier in NY and into the southern
Catskills (cannot rule out a few higher amounts, especially in
the higher terrain)...12 to 18 inches along the southern tier of
NY and into the nrn Catskills...and around 4 to 8 inches from
the nrn Finger Lakes into the srn Tug Hill.
The snow is expected to taper off west to east as the system
pulls out late tonight. Visibilities will improve rapidly around
sunrise with most of the lingering light snow after 7 am
dissipating just before noon. Conditions should remain dry
through the rest of the afternoon.
Temperatures will remain below average with lows tonight
dipping into the teens and lower 20s. Highs on Thursday will be
only reaching into the mid 20s to lower 30s.
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
330 AM Update...
CAA over Lake Ontario keeps cloud cover over the Finger Lakes
region into NE PA while eastern regions of central NY start to
clear as high pressure builds in Thursday night. With fresh
snow and dry air aloft, areas that clear in the eastern regions
of central NY and the Twin Tiers can see temperatures quickly
fall into the single digits while areas that stay cloudy keeps
overnight lows in the low 20s.
Friday, high pressure moves overhead with much of the remaining
clouds clearing. Friday night once again has a challenging
overnight low forecast with a disturbance moving in from the
west bring in clouds, mainly for the Finger lakes and the
western counties in the Twin Tiers region. Lows are currently
forecasted to be in the teens for these regions as the clouds
move in and reduce radiational cooling but changes in timing
will result in large changes both up or down. Everywhere else
will see lows down into the single digits.
SW flow ahead of a shortwave moving in from the Great Lakes on
Saturday brings in warmer air with highs back up around
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
330 AM Update...
Chances for snow showers arrive Saturday night, mainly north of
the PA border, as the trough swings from the Lower Midwest into
northern NY. A change over to a rain/snow mix is expected into
Sunday as temperatures climb back up into the mid and even upper
30s. We briefly dry out into Monday with some weak ridging.
However, later Monday night, a trough developing over southern
Canada will begin to dig into our region, which will bring in
our next chances for snow showers into Tuesday. Again, this will
be mainly north of the PA border, before high pressure
beginning to build in for the middle of next week brings an end
to precip chances.
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Snow, heavy at times, will continue to affect the terminals
through the overnight hours. IFR conditions will persist
through mid-morning Thursday. The heaviest snow will fall from
KAVP to KBGM, where we will see prolonged visibility
restrictions of 1/4SM to 1/2SM. Ceilings will fluctuate between
500 and 1500 feet. In addition, KAVP will experience LLWS
conditions as a low level jet moves over the terminal.
KITH and KELM will also experience visibility restrictions of
1/2SM or less through late tonight.
The snow will intensify at KSYR and KRME between 00z and 03z,
but isn`t expected to be as heavy as the snow to the south.
A mix of MVFR and IFR restrictions are expected by late Thursday
morning as a few snow showers continue to affect the region. VFR
conditions will develop from west to east between 18z Thursday
and 00z Friday.
Thursday night through Saturday night...VFR.
Sunday...Chance of rain/snow showers and associated
Monday...Generally VFR conditions with a few rain/snow showers
PA...Winter Storm Warning until 10 AM EST Thursday for PAZ038>040-
NY...Winter Storm Warning until 10 AM EST Thursday for NYZ044>046-
Winter Weather Advisory until 10 AM EST Thursday for NYZ009-
Winter Storm Warning until 7 AM EST Thursday for NYZ015-
Winter Weather Advisory until 7 AM EST Thursday for NYZ016-017.
Area Forecast Discussion
National Weather Service Denver/Boulder CO
825 PM MST Wed Dec 16 2020
Issued at 815 PM MST Wed Dec 16 2020
Minor updates to the forecast tonight. Blending of observed temps
into forecast on autopilot, and see no reason to adjust overnight
lows. Band of high clouds moving across the western slopes may
clip the western edge of our forecast area for a few hours. 01z
HRRR run has a good handle on these and blended in a little of
that model for the rest of the night. Otherwise terrain induced
overcast skies in the mountains and foothills. Berthoud pass
observation has 1/2 mile visbility in snow but with gust to 36 kts
more likely blowing snow on that ridgetop. CDOT webcams difficult
to decipher, but roads appear to be OK and snow not visible in
.SHORT TERM...(This evening through Thursday)
Issued at 210 PM MST Wed Dec 16 2020
The forecast is on track without significant changes today. Light
snowfall on west facing slopes west of the Continental Divide
continues to diminish, with stations and webcams reporting
gradually greater visibilities and higher cloud bases. Snowfall
should end late this evening as expected. We reduced QPF on the
mountain ridges around the Indian Peaks as models are likely
overestimating the remaining snowfall potential this evening as
they have been doing all day. Overnight lows will be a bit higher
tonight in areas not dominated by cold air pooling. Expect a near
seasonal normal overnight low in the upper teens or lower 20s in
the Denver metro area and Front Range foothills, with single
digits to low teens in the South Platte River Valley and much of
Lincoln County, and high teens elsewhere on the plains. The
mountains will see single digit overnight lows again.
The upper ridge will continue to advance over the Rockies tonight
and Colorado should be under the ridge axis by morning. Southerly
surface flow during the day will provide some warm advection to
offset the remaining snow cover, but the mountain valleys and
South Platte Valley will remain under stubborn inversions
throughout the day, resulting in chilly temps. Expect highs in
the 40s on the plains and 30s in the mountains. The next trough
will be advancing to the Rockies through the day. Ahead of it,
flow aloft over northeast Colorado will increase and turn
southwesterly, and upper level QG subsidence will be replaced by
weak ascent. Light snow may develop again on the west slopes to
the west of the Continental divide, but little to no QPF is
expected through midnight Thursday.
.LONG TERM...(Thursday night through Wednesday)
Issued at 300 PM MST Wed Dec 16 2020
The trough for Thursday night and Friday continues to fade a little
in the models. The best lift will rush across the mountains early
Friday morning and the plains by midday. There may be a shallow
layer of north winds, but on a larger scale, there will be northwest
winds not far off the ground that should keep a dry layer for the
expected light showers to fall into. There should be a period of
light snow for all the mountain areas, with a few heavier showers
possible. On the plains, it`s virga or light showers for a few hours
as the area of lift goes by. Previous snow amounts look good, mostly
2-4" in the mountains and an inch or less at lower elevations.
There`s another weak shortwave in strengthening northwest flow
Saturday. This should keep some moisture over the mountains and some
wave cloudiness. Behind this we`ll quickly get into warm advection
with a stable layer above the mountains. There should be some wave
amplification though the flow is not very strong yet on Saturday. By
Sunday the flow is stronger, and it looks like we`ll have a period
behind the Saturday trough with northerly flow at jet level which
could reflect the wave energy and provide more of a high wind threat
for the Front Range on Sunday. By Monday the flow is decreasing a
bit. Model blend is similar to the previous forecast, with
temperatures rising into the 50s for Sunday through Tuesday. There
will still be some wind in the mountains, but not much of a high
wind threat. There`s still pretty good agreement on a strong cold
front for Wednesday, but the lift and moisture now look like they`ll
mainly be north and northeast of Colorado. We could still get a
quick shot of light showers again, but the main impact will be the
cold front. The brunt of the cold air will likely also be east of
us, but dropping back into the 30s for a day still looks likely.
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 459 PM MST Wed Dec 16 2020
VFR through the period. Wind have calmed down at KAPA and shifted
to NW at KBJC. Wind forecast to remain from the NW at KBJC closer
to the foothills and mountain wind effects. At KAPA and KDEN
normal drainage regimes to bring generally southerly wind. Weak
upper level wave to enter the area Thursday, with lowering and
thickening clouds but remaining well above VFR limits. Toward mid
day Thursday a weak wind shift will move in on the plains,
affecting KDEN and KAPA with northeast flow for part of the day.
Area Forecast Discussion
National Weather Service Burlington VT
1034 PM EST Wed Dec 16 2020
Snow will overspread the North Country tonight through Thursday
morning. Snowfall accumulations will vary sharply across the
North Country with 6 to 12 inches expected across Rutland and
Windsor Counties, while a dusting to an inch or two is expected
further north over northern New York into northern Vermont. A
difficult morning commute is likely for many on Thursday, before
the snow tapers off to flurries by mid afternoon. Chilly
temperatures prevail the next couple of days, before a warming
trend develops by the weekend.
.NEAR TERM /THROUGH THURSDAY NIGHT/...
As of 946 PM EST Wednesday...Winter Storm Warning continues for
Rutland/Windsor for 6 to 10 inches of snowfall with localized
higher amounts possible south of Route 4, while winter wx
advisory continues for Addison and Orange counties for 2 to 6
inches of snow.
Overall forecast in good shape and no big changes needed at this
time. Only tweak was to up the timing just a bit as snow has
moved into Rutland County based on observations and webcams.
Rest of forecast remains unchanged.
No significant changes were made to this forecast package, just
minor adjustments to sharpen expected north-south snowfall
gradient, as guidance has come into better agreement.
Water vapor shows sharp mid/upper lvl trof acrs the Ohio Valley,
while IR sat indicates rapidly cooling cloud tops acrs central PA,
angling toward southern/central New England, as confluent flow
prevails acrs North Atlantic. I have to admit, the water vapor/satl
imagery with this developing system is pretty impressive this aftn,
especially the advection of moisture and the expanding coverage of
cooling cloud tops over central PA. Meanwhile, potent 5h vort is
helping to enhance 1010mb sfc low pres near Cape Hatteras per latest
analysis, while widespread precip continues to expand in areal
coverage over most of the eastern Conus. Noticing visibilities with
moderate to locally heavy snowfall in the 1/4 to 1/2sm range over
central Pa, with light snow already at KBGM. Our fcst challenge
remains unchanged, with how quickly mid/upper lvl circulation de-
amplifies in the fast confluent flow aloft and exact
placement/evolution of mesoscale band of moderate to heavy snowfall
acrs southern/central VT.
Consensus among meso-scale modeling supports 7h/5h circulation
moving from eastern PA into southern New England, while strong band
of 7h fgen forcing lifts pivots from the Catskills into southern VT.
The GEM/NAM and RAP show this band reaching southern Rutland/Windsor
Counties, while GFS/ECMWF is along the MA/VT state line. Latest
trends support the heaviest snowfall potential associated with this
band of enhanced fgen forcing mainly along and south of Route 4 acrs
Windsor/Rutland Counties. HREF highlights >60% of 1 to 1.5 inch per
hour snowfall rates acrs this area, with sharp northern side
weakening. These band structures and associated movement north,
along with enhanced snowfall rates are extremely difficult to
predict, and become a nowcasting event as they develop on the radar.
It should be noted snowfall amounts typically drop off sharply on
either side of these bands, as dynamics are weaker, uvvs in the
favorable snow growth is less favorable, resulting in lower snow
ratios. Utilizing a general consensus indicates the fgen band lifts
into extreme southern Rutland/Windsor Counties, before shifting to
the east. The SREF plume snowfall for VSF ranges from 2 inches to 26
inches, indicating the large spread acrs our southern areas. For our
messaging we will continue with a general 6 to 10 inches with
localized 12 inches or more possible south of Route 4, while amounts
quickly drop off acrs central and northern VT. If the band stays
south of our cwa, amounts will be much less. Snow ratios of 12 to 15
to 1 are likely within the mesoscale band with 10 to 13 to 1 outside
the band over most of central/northern Vt and eastern Dacks.
Snow develops btwn 02-04z acrs southern VT and spreads northward
into much of the dacks and northern/central VT btwn 04z-08z. The
heaviest snowfall rates occur btwn 09z-15z on Thurs, creating a
hazardous morning commute, especially southern/central cwa, with vis
below 1/2sm and snowfall rates of 1 to 1.5 inch per hour.
Mid/upper lvl trof axis lingers along with good 850 to 500mb
moisture through 18z Monday, before dissipating. Expecting snow to
linger acrs central/southern VT thru 18z, before tapering off to
scattered flurries by 21z.
Temps with thickening clouds tonight and snow developing hold in the
5F to 15F range, while warm into the mid teens to lower 20s on
Thurs. A chilly night with fresh snow pack is anticipated for
central/southern section on Thurs Night/Fri AM with lows 0F to +15F.
.SHORT TERM /FRIDAY THROUGH SATURDAY/...
As of 1032 PM EST Wednesday...Surface high pressure will settle
across the North Country Friday night giving way to clear skies and
overnight lows in the single digits. A relatively warmer day can be
expected on Saturday with highs in the upper 20s to low 30s as high
pressure moves offshore and the flow aloft becomes southwesterly.
Clouds will increase on Saturday as well associated with an upper
level low passing to the north during this time.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 1032 PM EST Wednesday...A series of upper-level shortwave
troughs will pass overhead early next week bringing a chance of
precipitation to the North Country. A decaying frontal boundary will
accompany said shortwave passages, though will likely become washed-
out as it traverses the forecast area. The best chance for
precipitation will be across northern New York Sunday afternoon and
into the overnight hours, mainly in the form of snow showers.
However, there could be a mix of rain/snow within the Saint Lawrence
Valley with the advection of relatively warmer air. By Monday
morning, showers will become more lake effect driven and confined to
areas downwind of Lake Ontario. Still, precipitation will be light
with little to no snow accumulation expected. High temperatures
Sunday and Monday will be in the mid to upper 30s with overnight
lows in the 20s.
Additional chances for precipitation exist Tuesday as another
shortwave trough passes to the north. Again, precipitation will
mainly be in the form of snow, though a mix of rain/snow is possible
within broader valleys. Little accumulation is expected during
this time. Temperatures will trend cooler thereafter with highs
in the 20s for mid- week.
.AVIATION /04Z THURSDAY THROUGH MONDAY/...
Through 00Z Friday...VFR conditions are expected through 06z
then as snow moves up into the region ceilings and visibilities
will lower into the 1 to 3 mile range, but 1/4 mile at KRUT
where snow will be heavy. Ceilings will lower into the 800 to
1500 foot range. Conditions will slowly improve into the MVFR
and VFR categories after 18z. One item of note...KMSS will be on
the edge of the snow and are expected to only see some snow
showers and conditions will be MVFR/VFR for the entire period.
Winds will generally be from the north at speeds of 10 knots or
Thursday Night: VFR. NO SIG WX.
Friday: VFR. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. Slight chance SHSN.
Sunday: Mainly VFR, with areas MVFR possible. Slight chance SHSN.
Sunday Night: Mainly MVFR, with areas IFR possible. Slight chance
Monday: Mainly MVFR, with local IFR possible. NO SIG WX.
VT...Winter Storm Warning until 4 PM EST Thursday for VTZ011-012-
Winter Weather Advisory until 4 PM EST Thursday for VTZ009-010-
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
259 PM PST Wed Dec 16 2020
.SYNOPSIS...A frontal system will bring widespread moderate to
briefly heavy rain to the area through tonight. Gusty evening
winds along the coast and overnight high elevation snow can also
be expected tonight. The precipitation will taper to lingering
showers on Thursday.
.DISCUSSION...After some areas of fog this morning, warm frontal
rains have been spreading across the area through the day. A cold
front will bring heavier rains later this afternoon and overnight.
Overall precipitation amounts look similar to last weekend`s
system (1-3 inches across most of the area with less than an inch
across Lake and S Mendocino counties), but there could be some
rainfall amounts over 3 inches across some SW facing mountainous
terrain of Del Norte and extreme northern Humboldt counties. The
bulk of the rain will fall tonight, with some lingering showers
into Thursday morning. There is a slight chance of thunderstorms
tonight, mainly over the coastal waters.
The most problematic part of the forecast is high elevation snow
amounts, particularly at Scott Mountain Pass tonight. The highest
QPF values area expected before 06Z, with snow levels beginning
to drop just after that time. Current observational data suggests
wet bulb temperatures several degrees above freezing across the
Trinity Horn (NE Trinity county), and models suggest snow levels
are likely just above pass level. Additionally, snow levels are
forecast to rise a bit more late this afternoon and perhaps early
this evening before falling overnight. This leaves a period between
about 9 PM and 3 AM when there will be some accumulating snow around
Scott Mountain Pass. At this time, it appears snow totals may top out
at around 2 inches at road level with more snow at higher
elevations. There may be a delay in the snow sticking to the ground
as well, as surface temperatures will be slightly above freezing and
the roadways will be wet. HRRR probabilistic guidance shows a 60%
probability of 2"> snow near the pass, with 30% of 4"> snow. At this
point, there is not enough certainty in over 2" of snow sticking to
the roadway to warrant a Snow Advisory, but the oncoming will
continue to monitor conditions through the evening for a possible
short fuse advisory.
After another break in the weather of Friday, another storm system
will bring mostly light rain generally N of Cape Mendocino. The
GFS and ECMWF models are in better agreement than yesterday, with
rains starting a bit later on Saturday and persisting into
.AVIATION...Flight categories vary across the CWA as frontal
boundaries pass through. KCEC is expected to remain in IFR until the
evening. Rain, lower visibility, wind gusts and wind shear are in
effect at the coastal terminals. KACV has been in VFR for most of
the day but is expected to diminish in the early evening and improve
overnight as winds ease and ceilings lift. Showers will continue
intermittently through the TAF period for the entire CWA with a
possible reprieve by late tomorrow morning. KUKI looks to have less
severity of wind shear but IFR with reduced visibility and rain.
Southerly winds are to switch to a NW bearing by tomorrow
.MARINE...Have continued the hazardous seas warning for the northern
outer waters this evening. Any one wave group may not quite be
meeting our criteria, but the combination of a west-northwest swell
currently around 11 to 14 feet at 15 seconds and some steep
southerly seas associated with strong winds ahead of a cold front is
resulting in some confused and rather hazardous sea conditions out
there. As that cold front passes by, winds will ease substantially
and shift to the southwest and west, then northwest overnight. The
swell will gradually decay, but will remain elevated into the 10 to
12 ft range into Friday. Another reinforcing swell projected around
10 to 12 ft at 15 seconds will arrive late Friday into Saturday,
probably resulting in continued Small Craft Advisories for all our
coastal waters into the weekend. Otherwise, moderate northwesterly
winds on Thursday in the wake of our front will diminish into
Friday, then shift back toward southerly for the weekend as another
front tries to approach from the north. These southerly winds may be
locally stronger and gusty toward or north of the Oregon border, but
do not look particularly strong in our waters. Thus, the swell will
likely be the main contributor to the overall sea state from Friday
through the weekend, as opposed to more locally-generated steeper
southerly seas. /AD
.BEACH HAZARDS...Elected to allow the high surf advisories to expire
at noon today. Looking at buoy data, there were probably still some
breaking waves around 17 to 20 feet at that hour, highest along the
Mendocino coast, but those have continued to come down steadily this
afternoon, well below advisory criteria. Expect there will still be
some 13 to 17 ft breakers into this evening along west-northwest-
facing beaches, and some pretty nasty conditions with the cold front
working through and southerly winds gusting to 30 mph locally near
exposed beaches and coastal headlands. /AD
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 9 AM Friday for PZZ450-455-475.
Hazardous Seas Warning until 8 PM this evening for PZZ470.
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Area Forecast Discussion
National Weather Service New York NY
750 PM EST Wed Dec 16 2020
High pressure to the north will slowly retreat as low pressure
moves northward up the Mid Atlantic coast. This low will
intensify as it approaches the region, turning east and passing
south of Long Island tonight into Thursday. High pressure will
then build in from the west through the first half of the
weekend before moving offshore late in the day Saturday. A
series of weak disturbances will move across the area Sunday and
Monday, followed by a stronger cold frontal passage Monday
night into Tuesday. High pressure will briefly return for the
middle of next week.
.NEAR TERM /THROUGH THURSDAY/...
Strong thermal forcing overrunning a 1037mb polar high centered
over eastern Canada, bleeding southward into southern New
England, has resulted in 2-3 inches of snow across portions of
the NYC metro, NE NJ, and Long Island, with snowfall rates of
1-2 inches an hour. This activity will overspread CT and the
Lower Hudson Valley the next couple of hours as cold, dry air
(dew points in the single digits to lower teens) saturates.
Thus far, the NAMNest, the warmer of the solutions aloft, was
handling the thermo profile best when compared to the 00Z OKX
sounding. It was around 0c at 825mb, while the GFS and HRRR were
several degrees cooler. Strong lift though will keep this area
generally isothermal and below freezing the next few hours. The
key here will be the position of the coastal front and how far
north and west the warm nose (around 750 mb) gets overnight.
There is even some evidence that the boundary layer will warm
sufficiently after midnight (due to east winds) for some rain
across eastern sections of Long Island and perhaps coastal SE
CT. The front end dump of snow may make this a moot point with
warning level snows likely achieved before this changeover even
happens later tonight.
Greatest pressure falls of 7mb in the last 3 hours just east of
the Delmarva with a 1004 mb low east Wallops Island, VA. The
low will continue to track northward and hug the coast, as a
negatively tilted shortwave trough works NE across the central
Appalachians. The low will eventually turn east running into the
blocking high over eastern Canada, passing south of Long Island
overnight into Thursday morning.
The primary question remains how far north the low will come
before making its eastward turn, which in turn dictates how
much, if any, warm air is able to work into the area at the
surface and aloft. From a big picture perspective, the models
have been very consistent with the position of the low over the
past 24 hours, with only minor changes from run to run. However,
given how close the low is forecast to come to the region, even
minor changes in the location of the low will have a
significant impact on snowfall totals, especially along the
In addition, high resolution models are indicating the
potential for a dry slot to develop across Long Island and
perhaps as far north as southern Connecticut. Model soundings
also indicate some loss of saturation in the dendritic growth
zone during this same period, all of which could at the very
least limit the intensity of precipitation, and possibly allow
precipitation to change to drizzle for a period. With that said,
global model soundings remain below freezing throughout the
event, keeping precipitation all snow.
Winds will become more northerly as the low pulls east towards
daybreak, which will allow colder air to filter back into the
region, changing precipitation back to snow everywhere. Snow
will eventually wrap up from west to east from late morning into
the early afternoon.
Snowfall accumulations will range from 12-18 inches across the
Lower Hudson Valley, interior northeast New Jersey, and interior
southwestern Connecticut, where precipitation will remain all
snow. Snow totals will range from 10-15 inches across much of
the New York City metro area and western Long Island, although
totals could be a few inches lower across coastal portions of
Brooklyn, Queens, and Nassau County. Across the rest of Long
Island and far southeastern Connecticut, snowfall totals will
range from 4-12 inches, lowest across the Twin Forks and
immediate south facing coastlines.
In addition to the snow, winds will increase this evening as
the deepening low approaches. Winds could gust to 35-45 mph
across much of the area overnight, with gusts to 45-55 mph
possible across far eastern Long Island. While these winds would
result in blizzard to near-blizzard conditions at times, they
also correspond with the greatest potential for mixing. With
that in mind, made no changes to headlines, with a Winter Storm
Warning remaining in effect for the entire area. While breezy
conditions will continue into the morning as precipitation
changes back to snow, with decreasing snowfall intensity
visibilities should remain above 1/4 mile.
.SHORT TERM /THURSDAY NIGHT/...
Winds will gradually diminish Thursday night as the low
continues to move east away from the area. With a fresh
snowpack, lows will range from the lower teens across typically
cooler interior locations to the low 20s along the coast.
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Not a whole lot of change in the global models from what we saw
24 hours ago. A progressive, yet amplified upper flow will
feature ridging building in from the west Friday into Saturday
with a broad upper trough reestablishing itself across the NE
quarter of the CONUS Sunday into early next week.
At the surface, high pressure settles over the area late Friday
night into Saturday morning before moving offshore late in the
day. Late Saturday night into Monday, a disjointed upper trough
will send a series of weak shortwaves into the area with a low
chance for light precipitation to the NW of NYC late Saturday
night into the first half of Sunday. It looks cold enough for
for light snow shower activity with little or no accumulation
expected. A cold front will then move across the area Tuesday
morning with some cooler air gradually filtering in through
Wednesday morning. The cold frontal passage looks to be dry, but
a rain or snow shower across the hills well north and west of
NYC is not out of the question.
Temperatures will gradually moderate through the period, with
readings 5 to 10 degrees below normal at the start, to slightly
above normal by early next week. Following a cold frontal
passage Tuesday morning, temperatures will return to near normal
Tuesday night and Wednesday.
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
***HIGH IMPACT WINTER STORM IN PROGRESS***
Low pressure moving NNE along the Mid Atlantic Coast tonight will
turn E off the New Jersey coast early Thursday morning, and then
pass S of Long Island through the day on Thursday.
Bands of moderate to heavy snow with LIFR conds are spreading into
the area attm. Some sleet should mix in along the coast for a couple
of hours after 05Z-06Z (KEWR/KJFK/KLGA/KISP and briefly at KTEB),
then precip should change back to light snow after 08Z-09Z.
ENE winds will ramp up quickly this evening to 30-35G40-45kt,
highest at KBDR with its Long Island Sound exposure. Wind shear is
also expected tonight, generally starting after 02Z and ending after
05Z in the NYC metros, and 07Z-08Z farther east. This will occur at
2000 ft with a ENE direction and speed of 50 to 55 kt.
Storm total snowfall of 10-16 inches is expected, with the higher
amts at the terminals NW of NYC.
Snow should gradually taper off from W-E through the day on Thu. VFR
conds with gradually diminishing N winds forecast through the day,
with a chance that MVFR cigs could last through the day.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
AMD possible to fine-tune flight cat and precip types.
.OUTLOOK FOR 00Z FRIDAY THROUGH MONDAY...
.Thursday night through Saturday...VFR.
.Sunday...Possibly MVFR at times with snow showers.
Detailed information, including hourly TAF wind component forecasts,
can be found at: http:/www.weather.gov/zny/n90
Winds will continue to increase on all waters this evening as a
strengthening area of low pressure approaches and moves across
the waters. A Storm Warning is effect on the ocean waters with
gusts 50-55 kt expected overnight. Elsewhere, Gale Warnings
remain in effect, with winds expected to gust to around 40 kt.
In addition, seas will continue to build, with 12-16 ft seas
expected on the ocean by Thursday morning and 3-7 ft on the Long
Winds will gradually diminish during the day on Thursday,
falling below SCA criteria on all waters by Thursday night,
although ocean seas will continue to remain elevated.
Northerly winds will continue to diminish Friday with high
pressure building across the waters into Saturday. The high
builds offshore late Saturday with a weak return flow into early
next week. Sub SCA conditions are then forecast into early next
A winter storm will bring liquid equivalent precipitation totals
of 1-1.5 inches through the day on Thursday, with the majority
falling through Thursday morning. Any melting should be slow as
high temperatures remain below 40 until the weekend.
Surge is expected to build to 2 1/2 to 3 1/2 ft in most spots across
Lower NY/NJ harbor, W LIS, and south shore bays of W LI on NE winds
ramping up to solid gale/marginal storm force this evening.
Widespread moderate coastal impacts are expected along the south
shore bays of Nassau County. Along W LI Sound, combo of 3-5 ft surf
and elevated water levels will bring minor to moderate coastal
impacts for shoreline roads and properties, particularly coastal
Westchester and NW LI.
Storm surge will likely peak out at 4-5 ft in spots tonight
during time of low tide, but then is likely to settle back to 2
1/2 to 3 1/2 ft during the times of high tide Thu
morning/afternoon as winds shift to the north. These water
levels, during a higher astronomical tide Thu AM/early aft, will
bring potential for more widespread minor to moderate coastal
impacts with Thursday morning/early aft high tide. Highest
probability of widespread moderate coastal flood impacts (2 to
locally 3 ft inundation) is along vulnerable south shore bays of
LI and Queens with limited tidal drainage, with widespread
minor to locally moderate impacts (1 to locally 2ft inundation)
elsewhere. Have stayed close to deterministic surge guidance and
NYHOPS weighted mean, with expectation of wind shifting to a
less conducive N flow for surge. Will have to monitor guidance
CT...Winter Storm Warning until 1 PM EST Thursday for CTZ005>012.
Coastal Flood Advisory from 9 AM to 2 PM EST Thursday for
Coastal Flood Advisory from 11 PM this evening to 2 AM EST
Thursday for CTZ009-010.
NY...Winter Storm Warning until 1 PM EST Thursday for NYZ067>075-
Coastal Flood Advisory until 3 AM EST Thursday for NYZ079>081.
Coastal Flood Advisory from 9 AM to 2 PM EST Thursday for
Coastal Flood Advisory until 1 AM EST Thursday for NYZ072-074-
Coastal Flood Advisory from 8 AM to 11 AM EST Thursday for
Coastal Flood Advisory from 11 PM this evening to 2 AM EST
Thursday for NYZ073-176.
Coastal Flood Warning until 1 AM EST Thursday for NYZ179.
Coastal Flood Warning from 8 AM to 2 PM EST Thursday for
Coastal Flood Warning from 11 PM this evening to 2 AM EST
Thursday for NYZ071-078-177.
NJ...Winter Storm Warning until 1 PM EST Thursday for NJZ002-004-
Coastal Flood Advisory until 1 AM EST Thursday for NJZ006-106-
Coastal Flood Advisory from 8 AM to 11 AM EST Thursday for
MARINE...Gale Warning until 1 PM EST Thursday for ANZ330-335-338-340-
Storm Warning until 7 AM EST Thursday for ANZ350-353-355.
Area Forecast Discussion
National Weather Service Blacksburg VA
924 PM EST Wed Dec 16 2020
Low pressure off the North Carolina coast will head north and
northeast off the mid- Atlantic by Thursday with wintry weather
ending tonight. Residual snow showers will be leftover along
our western slopes through Thursday night before surface high
pressure settles in Friday. High pressure stays in place into
Saturday before a weak system arrives late Saturday into
.NEAR TERM /THROUGH THURSDAY/...
As of 920 PM EST Wednesday
Winter storm ending, headlines will be cancelled.
Last of the precip is exiting the piedmont. Will see some
lingering snow showers/snizzle/freezing drizzle potential late
tonight across the western slopes but not enough to warrant
extending an advisory/warning. Given the main impact from the
storm is over, will be cancelling the warnings/advisories early.
However, will issue an SPS for slick roads for the overnight.
Previous discussion from early this evening...
Dry slot moving across the piedmont/foothills mid afternoon,
with deformation arriving in the mountains. HRRR and Nested NAM
and RAP have decent handle on where precip is, but still
differences in ptype. 18z RNK sounding showed a pronounced warm
nose to 4.2C above 850mb. This had led to mostly a freezing
rain/sleet event for the area today. Forecast model soundings
suggest cooling of the warm nose heading into the evening and
with some enhanced lift with the deformation zone, should be
some snow mixing into the mountains through this evening which
could lay down a 1 to 3 inch amount. We let the advisory expire
east as most temps are running above freezing and by the time
the precip exits the piedmont this evening, temperatures will be
back toward freezing. Still a threat of re-freeze so may issue
special wx statement to account for this.
Previous discussion from early this afternoon...
Wintry mix impacting most of the area overnight into Thursday
This system has been largely composed of a sleet and freezing rain
mix in our area. Some of the higher elevation locations had up to an
inch or inch and a half in the Greenbrier Valley early this morning,
but on the whole, sleet and freezing rain have been the order of the
day due to a warm nose around 850-750mb. Comparing the 16/12Z
sounding at RNK to the 16/18Z sounding currently in progress, that
warm layer has grown in magnitude (less than a degree Celsius this
morning, to ~4 degrees this afternoon). This indicates that the main
precip type in the NRV and likely much of the CWA will remain
sleet/freezing rain this afternoon.
This evening colder air will wrap around behind the system with some
enhanced northwest flow from an upper trough. As this erodes the
warm layer, things will slowly transition to snow, mostly along
mountain ridges from Greenbrier down to Tazewell, and perhaps in the
NC High Country. Upslope effects in these areas will serve to
enhance snowfall. There is a lesser chance of accumulating snow
reaching all the way east to the Blue Ridge, so outside of the
mountainous areas there may only be an inch or two. Lingering
upslope will last until around midnight and perhaps a little longer
in Western Greenbrier.
There is a possibility of a refreeze on the roads Thursday morning,
as some of the ice and snow from today melts and then cold morning
temperatures freeze it back up. The threat is greatest on untreated
roads and overpasses/bridges. Other than that, Thursday looks to be
a quiet weather day with highs in the 30s and low 40s as high
pressure approaches from the southeast CONUS.
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 115 PM EST Wednesday...
Quieter weather returns with a slight chance of some light
precipitation by Sunday.
Upper-level trough will be centered over the eastern United States
Friday night, with weak northwest flow keeping the chance for snow
showers for the western mountains. Any accumulations Friday night
should remain light. Snow showers will taper off Friday afternoon.
Tranquil weather is expected for Saturday as surface high pressure
builds overhead. High pressure shifts east as weak system approaches
our area from the west. It is possible there may be enough
antecedent cold air remaining that there could be a light mix
of rain/snow for the western portions of the CWA. It is very
unlikely this will be widespread and currently expecting little
to no snow accumulations.
Daytime temperatures will moderate each day through Saturday,
but overnight lows both Friday and Saturday will be cold. This
could allow for spots to refreeze overnight from any melting
that occurs during the day.
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 145 PM EST Wednesday...
Long term forecast highlights for Sunday some rain and snow,
followed by mostly warming weather.
A cold front will travel through our region Sunday with a chance for
rain and snow showers mainly in the west. Forecasted model soundings
support a mix of snow and rain showers Sunday morning, before
turning over to mostly just rain by the afternoon besides some of
the higher areas like western Greenbrier. Questions remain on the
development of low pressure center across the Gulf to Southeast. In
any case, this feature remains to our south. For Monday, more zonal
flow in the mid levels persist as a new, weaker upper level trough
per ECMWF and GEFS dips southward Monday night into Tuesday. A few
snow flurries may be possible along the western slopes. Temperatures
will moderate Tuesday into Wednesday, as a strong upper level trough
develops over the western/central U.S., setting us under a large
area of high pressure. A cold front approaches Wednesday night into
Thursday with a chance of rain and snow showers.
Medium confidence in the long term forecast.
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
As of 620 PM EST Wednesday...
Very poor flying conditions this evening into overnight
expected, especially along/west of the Blue Ridge, but even this
evening at LYH/DAN. The wintry wx will impact ROA/BCB/BLF/LWB
moreso than LYH/DAN.
Cigs should improve to MVFR east of the Blue Ridge between 05z-
10z, then scatter out Thu morning after sunup.
Across the mountains, low clouds are expected to linger til mid
morning, but should see it lifting to MVFR at ROA/BCB/LWB in the
11-17z time frame, with VFR at ROA by late morning.
BLF should keep IFR til midday, then MVFR though confidence is
low on the speed of this happening.
As for vsbys looking at IFR at times with wintry wx this
evening, then MVFR/IFR with fog til Thu morning for some
Flying conditions are poor with low ceilings and a mix of
mainly sleet and freezing rain across all local airports.
Ceilings will fall to low-end MVFR/IFR and visibilities down to
3SM or less in the widespread precipitation by 14Z.
Vsbys should become VFR by late morning Thursday.
Extended Aviation Discussion...
Lingering sub-VFR is possible into early Friday morning at
BLF/LWB, while rest of the area goes VFR. Expect VFR Friday into
the weekend, though a weak system may bring sub-VFR cigs to the
mountains Sat evening into Sunday. Most will keep VFR through
VA...Winter Storm Warning until midnight EST tonight for VAZ010>020-
Winter Weather Advisory until midnight EST tonight for VAZ007-
NC...Winter Storm Warning until midnight EST tonight for NCZ001-002-
WV...Winter Storm Warning until midnight EST tonight for WVZ042>044-
Area Forecast Discussion
National Weather Service Tulsa OK
810 PM CST Wed Dec 16 2020
The main change to the forecast this evening was to adjust the
fog forecast for the overnight into Thursday morning. Time height
plots of moisture indicate that the hydrolapse (rate of change of
humidity with height) is unfavorable for fog development across
much of eastern Oklahoma. However, conditions across the Ozark
Plateau (far northwest Arkansas and nearby areas of northeast
Oklahoma) appear much more favorable for fog development. One
caveat is the low clouds currently over the area. The 00Z HRRR
suggests that the west to east clearing trend observed on
satellite will continue thru the night, with areas mentioned
earlier clearing out after 09Z. So there appears to be a window
for the potential of fog development before the giant energy ball
starts heating things up Thursday morning. With temps below
freezing, if fog forms and is dense enough, slick spots could
develop on bridges and overpasses in freezing fog. Confidence
isn`t overly high, mainly because there`s really no guidance that
shows fog and there is still some uncertainty with the clearing of
the low clouds. If the low clouds don`t clear, the fog potential
would be much lower. Due to the lower confidence, will not issue
any headlines at this time. Will mention potential in graphics and
the Hazardous Weather Outlook.
.PREV DISCUSSION... /Issued 522 PM CST Wed Dec 16 2020/
CONCERNING TAF SITES KTUL/KRVS/KBVO/KMLC/KXNA/KFYV/KFSM/KROG.
Conditions will improve to VFR at the Oklahoma sites early this
evening, and at the Arkansas sites later tonight. VFR conditions
will then prevail for the rest of the forecast period.
PREV DISCUSSION... /Issued 228 PM CST Wed Dec 16 2020/
It`s another cold afternoon across the region today with highs
generally in the mid 30s across the forecast area under persistent
cloudiness. Clouds will begin to clear from west to east later
this afternoon and evening. Temperatures will drop into the mid to
low 20s for most areas tonight under surface high pressure. Some
areas where there is still substantial snow pack and where skies
clear could see temps drop into the upper teens. Some patchy
fog/freezing fog will also be possible mainly north of I-40
tomorrow morning where skies clear this evening.
Tomorrow... a mid-level ridge will build into the area which will
allow temperatures to rebound into the upper 40s - mid 50s under
sunny skies. Bumped temperatures up a bit mainly south of I-40
where there is no snow cover. Highs could remain a little cooler
in areas that received the greatest snowfall that will require
substantial melting tomorrow. By Friday, a mid level trough begins
to dig into the Desert Southwest which will bring southwesterly
flow aloft. This will aid in surface cyclogenesis across the High
Plains with a cold front stretching from the Northern Plains into
the Texas Panhandle by Friday morning. With a surface high
settling across the Southeast U.S., a tight surface pressure
gradient will form by Friday afternoon which will lead to strong
south winds on Friday with gusts in excess of 30 mph common across
northern Oklahoma as we mix into a strong 40-50kt low level jet
at 925mb. Cold front will pass through the area from northwest to
southeast on Friday night. With weak moisture return across much
of the area by Friday, expecting most areas north of I-40 to be
dry with best chances for some light showers across Southeast
Oklahoma where better moisture will be in place.
Saturday and beyond... Saturday will be a bit cooler in the wake
of the frontal passage with highs back down to near climatological
normal for this time of year. After Saturday, a warming trend will
begin as mid and upper level ridging builds into the area and
southwesterly downslope winds return to the area. Monday and
Tuesday will see highs well above normal with many places jumping
back into the 60s. The next strong cold front is currently
forecast to move through the area on Wednesday, but appears mostly
dry at this time. This will drop temperatures back down near
normal for Christmas Eve and into Christmas Day.
.PRELIMINARY POINT TEMPS/POPS...
TUL 24 49 35 56 / 0 0 0 0
FSM 27 51 30 57 / 0 0 0 0
MLC 26 54 35 56 / 0 0 0 0
BVO 22 48 31 54 / 0 0 0 0
FYV 23 49 28 55 / 0 0 0 0
BYV 24 47 30 54 / 0 0 0 0
MKO 24 46 32 55 / 0 0 0 0
MIO 24 47 31 55 / 0 0 0 0
F10 24 50 34 55 / 0 0 0 0
HHW 27 55 32 57 / 0 0 0 0