Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/18/22
Area Forecast Discussion
National Weather Service Indianapolis IN
1005 PM EST Sat Dec 17 2022
.Forecast Update...
Issued at 1005 PM EST Sat Dec 17 2022
...SLICK SPOTS POSSIBLE TONIGHT ESPECIALLY NORTH OF I-70 AND EAST
OF I-69...
Web cams were showing a dusting of snow at Anderson, Muncie and New
Castle and ILN also passed along some issues over their counties
north of I-70. After inter-office coordination, decided to ramp up,
the Special Weather Statement wording for those areas. Kept chance
PoPs in overnight supported by radar mosaic showing upstream snow
showers over north central Illinois, associated with an upper wave
rounding the base of the Great Lakes upper low. This feature will
move across north central Indiana overnight. A dusting appears
more and more likely north of I-70. However, thin saturated layer 2-
5K feet per BUFKIT and ACARS soundings and lack of strong lift
precludes anything more.
&&
.Short Term...(This evening through Sunday)
Issued at 211 PM EST Sat Dec 17 2022
- Overcast tonight with Scattered Flurries
Surface analysis early this afternoon shows deep low pressure in
place across eastern Lake Superior. The deep low was providing broad
cyclonic flow across Indiana and the Ohio Valley. GOES16 shows
abundant cloud cover across the area with any breaks across the area
filling in quickly due to daytime heating. Radar shows some flurries
across southern parts of Central Indiana and another area of
flurries was found over Central and northern IL. Aloft a weak short
wave was found entering Indiana, pushing east, and poised to pivot
around the low and across Central Indiana. Temps were in the upper
20s to lower 30s.
Tonight...
Models tonight suggest the short wave to the west will push across
Central Indiana, as the deep low to the north pushes east across the
Great Lakes effectively keeping broad cyclonic flow in place across
Central Indiana. Forecast soundings show ample saturation within the
lower and middle levels overnight as this wave passes with pwats
only around 0.25in. Models do suggest saturation in the dendritic
growth zone overnight. With some lift as the short wave passes,
chances for snow showers will be needed. Best moisture still looks
to remain across the northern parts of the forecast area. However
the HRRR suggests more of a uniform coverage of precipitation. Given
this, will trend toward low chance pops tonight with little to
minimal accumulations. With clouds but not much temperature
advection expected, will trend overnight lows toward the lower 20s.
Sunday...
Models suggest the large low pressure system to the north will
finally begin to drift east exiting the area. Within the upper flow,
weak ridging is noted across the plains as the low departs by midday
Sunday. This results in northwest flow aloft across Indiana and
subsidence on the lee side of the approaching ridge. Within the
lower levels a large area of cold high pressure is suggested to
stretch from the northern plains to the Tennessee Valley. Forecast
soundings and time heights trend toward a dry column amid the
subsidence. Thus we will expect a decreasing cloudiness type of day
with some sunshine expected by afternoon. The cold air that we have
recently experienced will be exiting east on Sunday, allowing some
warm air advection from the northwest. Thus this along with some
sunshine should allow highs to push into the lower 30s.
&&
.Long Term...(Sunday night through Saturday)
Issued at 211 PM EST Sat Dec 17 2022
* Continued cold with an Arctic blast arriving late in the period
* Mostly dry through early next week
* Potential for an impactful winter system late next week
Monday through Wednesday...
The beginning of the long term features a quasi-zonal pattern in the
wake the deep low departing to the northeast. Strong 1030mb surface
high pressure builds over the region Monday, then becomes centered
over the Northeast by midweek maintaining influence over the region
and keeping conditions mainly dry.
With high pressure directly overhead Monday, expect a larger diurnal
range in temperatures as optimal conditions set up for radiational
cooling Monday morning. Thin, high clouds stream in by Monday
afternoon ahead of a weak system developing in the Plains; however
enough solar heating should take place to allow the surface to
"warm" afternoon temperatures into the low to mid 30s.
Quiet yet cold conditions persist Tuesday as a weak system passes
just north of Indiana. Weak low pressure in the Plains weakens and
falls apart considerably as it ejects northeast through the Midwest
into an area dominated by high pressure. Main energy with this
system moves off into Central Ontario while the upper trough passes
by to the north. With such a disorganized system and such strong
surface high pressure maintaining influence near the surface, do not
expect impacts other than increased cloud cover.
Uncertainty begins to increase Tuesday night as longer range
ensemble and deterministic guidance disagree on the timing of the
arrival of a colder airmass to the north. Cross sectional analysis
reveals upper moisture and high clouds beginning to stream in from
the west Tuesday night and lowering into Wednesday. While conditions
for radiational cooling are not optimal, light northerly winds
overnight from the incoming arctic high should result in
temperatures dropping considerably overnight despite cloud cover.
Keeping lows Tuesday night in the upper teens across the north to
lower 20s in Southern Indiana.
Uncertainty continues to build into mid next week as guidance
struggles with the evolution of the major pattern change expected to
take place. While confidence is high in a much colder pattern
developing, the details regarding the transition period and
associated winter storm are lower. High pressure maintains influence
at the surface on Wednesday; however moisture streaming in aloft as
troughing begins to dig out west should result in persistent mid to
high clouds. Southerly return flow ahead of the developing system
likely will not reach the Ohio Valley by Wednesday as high pressure
to the north works to suppress everything southward, keeping a colder
airmass locked in place at the surface and highs generally in the
30s across the state.
*********************************************************************
Thursday through Saturday(Potential Winter System)...
Latest guidance continues to signal towards the potential for an
impactful low pressure system to pass through the Ohio Valley
sometime between Thursday morning and Friday. With that said, there
is still significant variability amongst both ensemble members and
various deterministic runs.
******************************************
Differences in Deterministic Solutions: *
******************************************
First, lets discuss the deterministic runs. The GFS has continued to
be an outlier, mainly due to the position of the ridge axis over the
Western CONUS. The American model has had the ridge axis over the
intermountain west, leading to a shorter wavelength and therefore a
neutrally tilted amplified trough over the Midwest.This solution
would result in more impacts over the eastern US versus the Midwest.
Of note is a slightly weaker thickness gradient prior to
cyclogenesis. With the high likelihood of a rather anomalous cold
sector within this system this leads to the belief that this
solution may be misleading. Another note to point out, deterministic
GFS solutions have not been consistent with the track of the system
over the past few days, waffling significantly from run to run...
leading to lower confidence in solutions. However, latest 12z run
today has trended in the direction of the ECMWF and other models
tracking the low through the Ohio Valley.
On the other hand is the remainder of the deterministic suite
(Canadian, ECMWF, UKMET). These three are much more aligned on the
ridge axis placement further west over the Pacific Coast. In return,
the wave length is larger, allowing for a more negatively tilted
upper trough and less subtropical jet influence. The polar jet in
this instance in piece-wise with a strong jet streak upstream of the
trough and a supergeostrophic jet streak near the ridge over the
Northeast. A coupled jet streak provides an efficient environment
for surface cyclogenesis, as seen near the surface of these various
solutions. All three of these solutions also seem to better
represent the anomalous Arctic air expected in the cold sector,
increasing baroclinicity and the rate of surface pressure depletion.
This is not to say that these solutions will end up being the result
next week, but the meteorological interactions over the 150 hours of
output do have plausible explanations.
Another note for the ECMWF solutions, while there has been some
waffling (which is expected) regarding timing and track of the
system. There has been significantly more consistency in the ECMWF
track and timing compared to the GFS... resulting in increasing
confidence in an ECMWF based solution with a powerful low pressure
system deepening and tracking through the Ohio Valley.
**********************************
Ensemble and Probabilistic Output: *
**********************************
These deterministic solutions can help dissect the probabilistic output
given through various ensemble members of each parent model. With
the conceptual model chosen (longer wave length, positively tiled
trough, coupled polar jet), we can narrow the expected solutions to
those that align. There is still a wide range of solutions even
through this process, but this does show a trend of some sort of
deep surface cyclone over the Midwest, Ohio Valley, or Tennessee
Valley Thursday into Friday. This leads to a greater likelihood of
an impactful winter storm within the vicinity of central Indiana.
The track of the surface low will still have a significant influence
on the severity and type of impact central Indiana will witness. Any
track south of central Indiana will lead to a greater chance of
significant snow fall, whereas north or through central Indiana will
limit snow, but increase rain and even thunderstorm chances.
This process also shows a wide array of temperature outcomes for
late next week, ranging from low 50s in the warm sector, to mid 20s
in the cold sector. For now, temperature forecasts are more aligned
with the ensemble mean, but the result with much more likely be on
the lower or higher extremes (10th or 90th percentile).
****************************************************
Winter Storm and Arctic Outbreak Brief Conclusion:
****************************************************
Through a diagnostic synoptic process, discussed above, trends are
leaning towards an impactful low pressure system with a low track
ranging from Chicago to Nashville. Many potential solutions and
outcomes remain in play including the potential for significant
snowfall sometime between Thursday morning and Friday. There are
still many factors that will influence the forecast in the coming
days ans this system will continued to be monitored very closely.
Despite uncertainties regarding the potential winter storm Thursday
into Friday, there are a few areas where forecast confidence is very
high. No matter the track of the upcoming storm system, confidence
remains very high that some of the coldest air of the year will
arrive by the holiday weekend with temperatures potentially falling
below zero! Any snowpack will further allow temperatures to plummet
into the negatives and possibly into record territory. Signals for
an arctic outbreak are strong, so while there may be uncertainties,
one thing that is certain is the extremely cold air coming down from
the arctic. Along with the cold air will likely be dangerously cold
wind chill with values possibly below -20F. Take precautions now to
prepare for the upcoming brutally cold weather this holiday
weekend.
********************************
Long Term Forecast Updates
********************************
Increased winds and gusts Thursday through Saturday morning toward
NBM 90th percentile to account for significantly strengthening storm
system in the region and to match with neighboring offices. Lowered
temperatures towards NBM 25th percentile Friday into the weekend to
account for NBM likely not catching the full extend of the cold air
coming that time frame. Kept PoPs as is for now as there is still
too much discrepancy within deterministic guidance to deviate from
NBM on timing of precipitation.
&&
.Aviation...(00Z TAF Issuance)
Issued at 614 PM EST Sat Dec 17 2022
Impacts:
- MVFR/VFR ceilings improving to VFR after 11z-15z Sunday
- Light snow showers and flurries ending after 04z-06z
- Winds 260-280 degrees near 10 knots
Discussion:
Impulse around the base of a Great Lakes upper low will
result in MVFR/VFR stratus and light snow showers and flurries
tonight. Flying conditions will improve to all VFR toward midday
Sunday as the low moves to the east and high pressure builds in in
its wake.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...MK
Short Term...Puma
Long Term...CM
Aviation...MK
Area Forecast Discussion
National Weather Service North Platte NE
521 PM CST Sat Dec 17 2022
...New Aviation discussion...
.SYNOPSIS...
Issued at 411 PM CST Sat Dec 17 2022
The powerful low pressure that was responsible for days of blizzard
conditions has pulled into the Great Lakes region. High pressure has
settled in at the surface while a ridge tries to build in to the
west aloft. A few light snow showers or flurries also skirted the
far north this morning and early afternoon. A deep snowpack of
greater than a foot remains across the northern Sandhills, while
patches of bare ground are showing in southwest Nebraska.
Key points:
- One cold front crosses the forecast area late Sunday or early
Monday, which brings the first wave of Arctic air. The result is
dangerously cold wind chills below -20 across the Sandhills
Monday and Tuesday nights.
- A potentially stronger system affects the area Wednesday into
Thursday. The result is snow, strong winds, and life-threatening
wind chills of -40 or colder Wednesday and Thursday nights.
- A Wind Chill Watch was issued for counties that first observe
these wind chills, but an expansion will likely be needed later
this week for the south. Additional possible headlines for wind
and snow will be determined on later shifts.
&&
.SHORT TERM...(This evening through Sunday night)
Issued at 411 PM CST Sat Dec 17 2022
This evening into tonight... The upper ridge over the Western US
flattens somewhat over the High Plains as a fairly weak surface low
emerges near the Black Hills and swings a boundary through the
Sandhills. Surface winds transition to southerly and modest WAA
occurs at H85. Included an area of fog along and ahead of the
boundary overnight into early Sunday morning where moisture
convergence occurs, especially over the snowpack. Confidence is too
low regarding visibility issues (e.g. advisory), but a narrow strip
of thicker fog cannot be ruled out. Very shallow moisture and the
lack of overall lift should keep all weather as fog or stratus
rather than drizzle/snow. Mostly clear skies and waning winds for
the first part of the night should allow temperatures to drop fairly
rapidly despite the aforementioned WAA. Boundary layer decoupling
and radiational cooling will likely be enhanced over the snowpack
area. Went ahead and trended min temps toward the cooler guidance.
Forecast lows range from single digits below zero in the far north
to the mid single digits in the south.
Sunday and Sunday night... A slightly deeper surface low spins up
near the CO/KS line, which will pull a warm front to our doorstep.
The southeastern CWA counties will likely surpass 40F for highs,
while western counties remain in the 30s, and northern counties
where the front doesn`t reach and the deep snowpack remains will
struggle to leave the 20s. The low will also switch the surface
winds back to north/northeasterly by evening time and will spread
clouds over much of the area. Forecast soundings suggest very
shallow moisture once again and rather weak lift. Kept all PoP
mention out for now, but wouldn`t be surprised should flurries or
light snow showers develop in the southeast counties near the front.
Overnight into early Monday, strong CAA already takes hold over the
northwest. Min temps approach -10F, compared to single digits above
zero toward central Neb. As of now, winds appear to be just light
enough to limit advisory conditions, but wind chill values still
drop pretty low in the far north (-15 or colder).
.LONG TERM...(Monday through Saturday)
Issued at 411 PM CST Sat Dec 17 2022
The extended forecast centers around the arrival of the coldest air
of the season thus far and life-threatening wind chill values. The
potential for high winds and accumulating snow present additional
challenges that will need fine-tuned over the coming days.
Monday and Tuesday... The first wave of Arctic air takes hold as H85
temps drop to as low as -15C across the north. A rather "normally"
strong high pressure of 1036mb settles onto the Plains by Tuesday.
The result will be highs in the single digits across the north and
teens for the south. Morning lows will range from near zero in the
far south to -15F in the far north, again air temps. Factor in a
light breeze and wind chill values drop below -20 basically near and
north of Hwy 2. Valentine and vicinity approaches -30 Tuesday
morning.
Wednesday and Thursday... A second system crosses the Plains later
on Wednesday, while an anomalously strong high pressure (1060mb?)
settles in its wake. The sheer pressure gradient between the surface
low and the high behind the cold front is staggering, which may
exceed 50mb. Some guidance suggests sustained hourly pressure rises
of 4+ mb in western Nebraska. When coupled with a 1.5PVU anomaly
reaching as low as 500mb and the northern stream H3 jet containing a
streak up to 170 kts, a period of high winds is possible. As of now,
the main clustering of solutions lie in the 25-40kt range for gusts.
As for snow, the main potential comes Wednesday night into Thursday
morning. Better moisture sits east of the forecast area, but light
accumulations are certainly possible near and east of Highway 83.
This also falls in line with the latest WPC extended outlook. High
temperatures will likely stay below zero for the Sandhills on
Thursday, and some guidance suggests the south won`t leave the
negatives either. Regardless, widespread wind chill warning criteria
(-30 or colder) are looking likely Wednesday and Thursday nights,
with values possibly reaching -50 near the South Dakota border.
Serious impacts are expected to ranching operations and other
outdoor activities.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 520 PM CST Sat Dec 17 2022
Poor flying conditions will are developing across north central
Nebraska.
A narrow plume of moisture associated with a warm front is
evident in satellite imagery streaming into Nebraska from the
north. As this moisture moves over a fresh, cold snowpack and
cools from below expect this will result in development of low
stratus and fog shortly after sunset with conditions at KVTN
trending from MVFR to IFR early in the period. A TEMPO to LIFR in
freezing fog also appears likely and may result in some icing of
aircraft surfaces. Poor flying conditions will diminish after
daybreak with VFR expected from mid morning onward. However a cold
front will move down form the north and bring a return to MVFR or
IFR conditions toward the end of the valid period.
However further to the south beyond the extent of the moisture
plume, the signal for sub-VFR conditions is subtle. Will indicate
VFR conditions through the period for more southern location
including at KLBF but will monitor closely for any development of
low clouds or fog.
Winds will generally be light through the period. The low level
wind field will increase overnight but the strongest winds will
slide by to our east so low level wind shear does not appear
likely at TAF sites.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Wind Chill Watch from late Monday night through Friday afternoon
for NEZ004>010-023>029-035>038-094.
&&
$$
SYNOPSIS...Snively
SHORT TERM...Snively
LONG TERM...Snively
AVIATION...MBS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
720 PM CST Sat Dec 17 2022
.UPDATE...
Issued at 721 PM CST Sat Dec 17 2022
Have made some minor adjustments to snow shower/flurry forecast
for tonight. Over the past couple hours, have seen an area of
light snow blossoming over western WI, with this activity heading
toward northern IL. Couldn`t find any model guidance with a handle
on this activity and hard to key in on any identifiable shortwave
in water vapor imagery responsible for this recent enhancement of
light snow. However, this light snow is blossoming within an arc
of higher moisture/implied ascent on low level water vapor
channel. Have also seen an uptick in very light echos (likely
flurries) across southern WI and northern IL. Have beefed up pops
somewhat and hit the flurry chances harder in the grids and
forecast tonight. If the activity over western WI holds together,
will need another update to beef up snow chances after midnight as
well, especially northern CWA. Not expecting snow to amount to
much, but an slight coating is possible with any heavier snow
burst, which given temps could lead to some patchy slick spots.
Updated grids and text products have been sent.
- Izzi
&&
.SHORT TERM...
Issued at 143 PM CST Sat Dec 17 2022
Through Sunday night...
The forecast messages for the rest of this weekend are:
* Spotty snow showers this evening but not at the intensity of
snow showers seen yesterday / last night.
* Clouds being stubborn to depart throughout Sunday, especially
the Chicago metro into northwest Indiana
Deep cyclonic flow continues across the entire Great Lakes and
Corn Belt regions from a closed low across central Ontario. The
depth of the saturated layer has diminished some today, per
satellite and aircraft soundings, as well as just visually seeing
some hints of brightness (or less opaqueness) outside. For much of
the day, the forecast area has been under a corridor of negative
vorticity advection (NVA) resulting in much less snow shower and
flurry coverage. There are two last upstream sheared waves, which
as of 130 PM are just southwest of the Quad Cities and in
southwest Minnesota. These will rotate within the cyclonic flow
near/just south of I-80 area late in the afternoon through the
evening. Each of these will re-enhance the lift and saturated
depth slightly, as well as cool the cloud layer a smidge bringing
it back into the dendritic growth zone (DGZ), resulting in an
uptick in flurries and spotty to scattered snow showers. With
these vorticity maxima being more sheared and the moisture depth
having diminished, the snow shower intensity is unlikely to be
what it was at times the last 48 hours. Still, with it being after
dark, spotty dustings may occur, and to a lesser degree than the
last couple nights, spotty black ice may return.
Temperatures have gone nowhere today with the clouds and westerly
winds gusting to 25 to 30 mph. These should continue a steady
trend this evening before a slow fall overnight. The rate of drop
will only be slight given the expectations for clouds to remain.
Forecast soundings show the saturation becoming thin by Sunday
morning, however with the subsidence inversion strengthening in
tandem with height rises, what is left of the clouds may very
well get caught underneath this inversion. Feel that this will be
the case given the guidance trend and how the RAP and HRRR have
consistently been showing clouds sluggish to depart. Confidence
is low in just how long the clouds persist though. By late
morning, much of the western and southern halves of the forecast
area could be clear, and then by early afternoon the sun may break
out over Chicago. But have trended later with the departure with
eastward extent in our forecast area given how guidance as a whole
tends to be too quick with departure in these setups. If clearing
has occurred by evening, with ridging passing over the area,
temperatures that will have only peaked in the mid 20s could drop
sharply. Some single digit lows may unfold for outlying areas.
MTF
&&
.LONG TERM...
Issued at 300 PM CST Sat Dec 17 2022
Monday through Saturday...
Key Messages:
* Brief chance for snow (possibly ending with freezing drizzle?)
Monday PM into Tuesday AM with no more than a dusting expected
* Strong winds, some snow, and bitter cold arriving late week
resulting in travel impacts heading into the holiday weekend.
* Confidence is increasing in an impactful winter system,
potentially significant, somewhere in the region. Still too soon
to discuss details!
* Now is the time to complete your winter prep for your home and
car if you haven`t already!
At the start of the extended period, Monday will start off chilly
with early morning low temperatures potentially in the teens and
near the single digits in outside of the Chicago metro. A weak
disturbance will begin lifting toward the area during the day
which could bring the potential for a quick hit of snow late
Monday into Tuesday morning. At this time it does not look overly
impactful, with perhaps a dusting of snow possible mainly
northwest of a LaSalle to Chicago line. There are hints that we
could briefly transition over to light freezing drizzle or
"snizzle" on the back edge of the system early Tuesday with the
loss of cloud ice as mid-level moisture exits a bit quicker than
in the low levels. Always want to watch out for those "event
before the event" scenarios that can always sneak up on us but for
now impacts with this system appear low.
It is also worth acknowledging the elephant in the room, which is
that there are model solutions suggesting a potentially higher
impact winter weather scenario may unfold somewhere in the region
during the Thursday-Friday timeframe, a peak travel period heading
into the upcoming holiday weekend. We are monitoring this very
closely, though we want to add that there remains a lot of
uncertainty in how things will ultimately unfold given it is still
several days away and urge caution to not lock onto specific
operational model runs as there remains a lot of spread among the
various ensembles. We encourage everyone to stay up to date with
the latest forecasts over the coming days as we get closer and
confidence in how this event will ultimately play out increases.
Where confidence is higher, however, is in the potential for at
least some accumulating snow falling across the area during the
Wednesday night-Friday timeframe, which combined with gusty winds
would result in some travel impacts and bitter cold wind chills
below zero heading into the holiday weekend -- regardless of how
much snow ends up falling and how high the winds end up getting.
If you haven`t already, winter prep for your home and vehicles
should be done early in the week!
The last thing to add is that due to the long stretch of below
freezing temperatures anticipated and resultant higher river
levels from this past week`s rainfall, there will be an increased
risk for ice jams along area rivers.
Petr
&&
.AVIATION...
For the 00Z TAFs...
Aviation weather concerns for the 00Z TAFs:
* Continued widespread MVFR ceilings overnight, then gradually
becoming VFR by late morning and scattering in the evening.
* Light off and on snow flurries until around midnight tonight.
* Snow showers likely this evening, with occasional IFR
visibilities possible but very little if any accumulation.
* Westerly winds with gusts of 20 to 25 kt.
Upstream observations are showing MVFR vsbys with a few areas of
IFR in the steadier snow bands, but most locations are seeing just
flurries with minimal reductions. Confidence is not high on the
vsby trends locally this evening, but the duration of any heavier
bands should be fairly brief. Confidence also is not high on the
end time of the flurries, as these have a tendency to linger in a
cold and moist airmass.
Lenning
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters until 9 AM Sunday.
&&
$$
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