Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/20/22
Area Forecast Discussion
National Weather Service Louisville KY
909 PM EST Wed Jan 19 2022
.Forecast Update...
Issued at 855 PM EST Wed Jan 19 2022
Well...Arctic front just passed thru SDF...and latest AMDAR sounding
(SDF to MDW) from 0054z has big dry layer 900 mb to 720 mb. This
corresponds well with mid deck cloud ceilings from MDH thru EVV and
up to HNB. This area has much limited precip shield and pireps have
been reporting lgt to mdt chop in this area.
Meanwhile further south a large rain shield is along and south of
the parkways. Cold front pushing east and the precip shield from W
KY with strong nw winds pushing it east. There is a brief thin area
of sleet from Butler, Warren, and Grayson counties on dual pol and
wx reports. This transition will not last long, before turning over
to all snow in next 90 min.
Between 930 est and 2 am...there will be the 4 to 5 hour of
accumulating snow between the parkways. Still like 1 to 3 in this
area. Further north we are contemplating on how to handle areas
along and north of the Ohio River in S IN.
This just in...light snow at the NWS office and temps have dropped 5
degrees in last 2 hrs.
&&
.Short Term...(Tonight through Thursday evening)
Issued at 249 PM EST Wed Jan 19 2022
...Accumulating Snow Still Expected Tonight...
By 00Z the cold front will be just exiting the southeast corner of
the LMK CWA in the Lake Cumberland region, ushering in much colder
air. Patchy light rain has developed along and ahead of the front
from Kentucky to Texas, with light snow behind the boundary over the
Midwest. As cold air pours into the region, light rain this
afternoon will transition to snow this evening into the late night
hours. A wintry mix is possible during the transition, but should be
fairly quick as the cold air pushes in...likely less than two hours
at any one spot. The snow and the cold are the larger stories for
tonight.
Snow will fall tonight as the upper trough axis remains off to our
west this evening and a 5H speed max swings into the Tennessee
Valley late tonight. Cross-sections and soundings show high RH in
the DGZ. There is also some negative EPV present but it is quite
weak, and theta-e surfaces show little if any instability. Mid-level
frontogenesis is much weaker than what we saw with the January 6
event and moves through more quickly. So, a broad area of light snow
is expected, with possibly some embedded moderately enhanced bands
of snowfall. HREF shows only a very small chance of snowfall rates
exceeding an inch per hour, and only for a couple of hours late
tonight. The most likely area to be affected by any locally higher
snowfalls would be the southern Blue Grass, generally from the
Lebanon and Danville areas ENE into eastern Kentucky. Will still go
with general amounts of 1-3" in the advisory area, with perhaps 2-4"
in the Blue Grass.
Unfortunately confidence in snowfall totals has actually decreased
today, with some data sources coming in with lesser amounts of snow.
WPC Super Ensemble at Lexington shows a mean of 1.5" and almost all
members are below 3.5". However, WSSI does still support advisory-
level snow and there is enough support in the data to stick with the
higher amounts we had been advertising previously.
In addition, winds behind the front will become gusty tonight, with
gusts of 20-25mph possible (gusts over 30 mph have been observed
upstream). For anyone out on the roads tonight (which is not
recommended) this will add to the difficult conditions in driving
snow. Wind chills will fall into the 5-15 degree range by morning.
Road surface temperatures are expected to fall below freezing around
midnight, and air temperatures will bottom out in the upper teens to
lower 20s by dawn. So, any moisture that freezes from the rain this
afternoon plus snow on top of it will rapidly lead to snowy/icy
conditions that will likely persist into Thursday.
Tomorrow will be much quieter with winds subsiding and no
precipitation expected with partly to mostly cloudy skies as strong
high pressure advances from the Dakotas to Iowa. Temperatures will
mostly stay in the 20s.
&&
.Long Term...(After midnight Thursday night through Wednesday)
Issued at 300 PM EST Wed Jan 19 2022
The main story for the long term will be the below normal
temperatures for the bulk of the forecast period. Long range
forecast models 7-day temperature anomalies have KY ranging 5 to 10
degrees below normal. This matches up with the 5 to 7 day 500 mb
anomalies from both the EURO/GFS showing a general troughiness
across the eastern half of the CONUS with ridging across the western
US.
Strong arctic high settles in over the Ohio Valley to end the work
week. Lows to start Friday will be cold with morning minimums in the
low/mid teens, despite sunshine and good subsidence from the sfc
high, highs in the afternoon will only reach the mid/upper 20s.
A few weak shortwaves will propagate through the Great Lakes over
the weekend but per model soundings, we will remain too dry in the
low levels for there to be any precipitation. Highs will be in the
low/mid 30s on Saturday and a few ticks warmer Sunday in the
mid/upper 30s.
Our attention then turns to the possibility of another storm system
impacting the Ohio Valley by Tuesday. Cut-off low over the Gulf of
California will eject eastward across TX Monday into Tuesday as an
upper-level trough drops southward over the Dakotas and into the
Great Lakes by Tuesday. Long range models tend to agree that a sfc
low develops along the LA Gulf coast Monday night into Tuesday
morning but differ significantly on how deep the trough becomes over
the Great Lakes and on the strength of the system as it tracks along
the Gulf Coast into the southeastern US by Tuesday evening. For now,
will introduce the slight chance of rain/snow across most of KY on
Tuesday with highs in the mid/upper 30s.
&&
.Aviation...(00Z TAF Issuance)
Issued at 605 PM EST Wed Jan 19 2022
Main impacts:
-- Precip type changeover this evening
-- Gust potential, BWG/LEX wind shift
-- Low ceilings, and low vis in snow
Discussion: Wind shift associated with the Arctic cold front is
through HNB and SDF, and on the doorstep of BWG. Precip is still all
rain, though anything that gets into HNB now will immediately be
snow. Changeover is pending at all three sites in KY, and could have
a period of SNPL mix before going to all snow late this evening.
Cig/vis should both drop into IFR once precip is all snow, and
should stay that way until just after midnight. Best chances and
most persistent IFR will be in LEX, whereas snow will hang on the
longest at SDF, possibly until the end of the inbound traffic push
around 08-09Z. Wind gusts from the N or NNW will be just shy of 20
kt.
Will break out to a mid-level deck before daybreak, but expect a
stratus deck to fill in with morning mixing, leaving ceilings in the
barely-VFR category for a lot of the day.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 8 AM EST /7 AM CST/ Thursday for
INZ084-089>092.
KY...Winter Weather Advisory until 8 AM EST /7 AM CST/ Thursday for
KYZ023>043-045>049-053>057-061>067-070>078-081-082.
&&
$$
Update...JDG
Short Term...13
Long Term...BTN
Aviation...RAS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
942 PM CST Wed Jan 19 2022
.UPDATE...
Issued at 911 PM CST Wed Jan 19 2022
The forecast remains on track this evening for lake-effect snow
showers to move through portions of northwest Indiana. Radar
trends this evening have continued to show bands of snow showers
developing and moving on shore east of Gary, IN with more recent
scans showing a more dominant band developing just offshore of
western Lower Michigan. Forecast soundings continue to show a
favorable environment across portions of Porter County with ample
low-level moisture, steep low-level lapse rates, and strong ascent
forcing going through the snow growth region. Some uncertainty
still remains in where exactly the best convergence axis and the
aforementioned dominant band will set up, but hazardous travel
from snow covered roads and reduced visibilities due to steady
snow should be expected through the night and into the day
Thursday. For this threat, the Winter Weather Advisory remains in
effect until 6 PM CST Thursday evening.
For the rest of the forecast area, we are in for a quiet and
bitterly cold night with temperatures continuing to drop into the
single digits. Blustery north-northwest winds will also continue
gust around 20 to 25 mph which will create very cold subzero wind
chills in the minus 10 to minus 20 range heading into Thursday
morning. Temperatures on Thursday will remain cold with highs
struggling to reach 20 degrees, but skies will be mostly cloud-
free for northeastern Illinois with partly cloudy skies for
portions of northwest Indiana not experiencing lake-effect snow
showers.
Yack
&&
.SHORT TERM...
Issued at 315 PM CST Wed Jan 19 2022
Through Thursday night...
The two primary areas of interest in the short term forecast
continue to be the swath of lake-effect snow slated to move over
portions of northwest Indiana tonight and tomorrow and the bitter
cold expected the next couple of nights. No changes were made to
the going Winter Weather Advisory that goes into effect at 6pm
this evening and is currently set to expire at 6pm Thursday for
Porter County.
Lake effect snow has already begun to fall over parts of
southwestern Michigan and will scoot southward along the lakeshore
over the next several hours. Snow is anticipated to begin falling
on northeastern Porter County as early as around 4:00 PM and
propagate southwestward to include much of Porter County and
portions of northern and eastern Lake County shortly thereafter
with light flurries possible in surrounding areas. Most model
guidance has been contaminated by the National Ice Center`s
January 18th ice analysis and says that most of the Illinois and
Indiana nearshore zones of Lake Michigan are ice-covered heavily
limiting the amount of fetch over this area as well as positioning
the land breeze convergence farther east than it may end up in
reality. However, since the portion of the lake that plays into
this system is practically ice-free, this means the coverage of
accumulating snow will likely be stretched ~5-10 miles west of
where most model guidance suggests.
Snow rates will pick up through the evening with the
heaviest rates occurring in northern Porter County overnight and
into early to mid tomorrow morning when we see the greatest
amount of low level convergence and vertical motion in conjunction
with sfc-850mb lapse rates of 7 K/Km or greater and lake-induced
EL`s over 7,000 ft. At this time, snow rates could reach upwards
of one inch per hour in this area. This spawns concerns regarding
the morning commute tomorrow, particularly along the I-80/90/94
corridors as well as I-65 north of Rt. 30. Slippery road
conditions and reduced visibilities can be expected through the
entirety of the morning commute. If you`re driving in this area
tomorrow morning, allow yourself plenty of extra travel time. This
snow will lighten up through the morning though remain in the
area through much of the afternoon. Some guidance is picking up on
the potential development of a mesolow tomorrow afternoon which
could keep the snow, albeit lighter snow, falling in the area
through at least Thursday evening. At this time, some light
flurries are also possible near the Illinois lakeshore.
The highest snow totals will likely be found in northern and
northeastern Porter County where several inches are probable, with
localized 6"+ amounts possible. Big question is do we see this
occur with a longer duration of light to moderate rates, or does
an intense single band move in by Thursday morning as shown by
some of the recent CAM solutions. Observational trends will need
to be monitored closely this evening. Should confidence increase
on heavy snowfall rates and higher impacts to the Thursday morning
commute, may need to consider a warning upgrade. The rest of
Porter County and northeastern Lake County are expected to receive
around an inch of snow. All the while, the rest of the CWA will
remain precipitation-free through the short term.
In other news, a cold air mass being pulled in from the northwest
and fueled by a positively tilted trough aloft will drop
temperatures into the single digits for most of the CWA by early
tomorrow morning. Gusts near 20 mph will pull wind chills down below
zero area-wide with wind chills around 15 below zero expected in the
far west suburbs and approaching 20 below zero in the far
northwest CWA. Highs reaching only the teens tomorrow will be
followed by another night with temperatures dropping into the
single digits and likely below zero for some. Calm winds tomorrow
night and Friday morning, however, will not result in much of a
wind chill factor.
Doom/Castro
&&
.LONG TERM...
Issued at 315 PM CST Wed Jan 19 2022
Friday through Wednesday...
The theme through the long term an unsettled and colder than
normal pattern, with multiple snow chances this weekend into
early next week. Anomalous western ridging (+PNA) will connect
with ridging spiking to the north of Alaska (-EPO), keeping a deep
mid-level trough axis centered from Hudson Bay through the Great
Lakes, favoring the colder than normal temperature regime. None
of the systems look particularly moisture-laden, but do have
favorable cold thermal profiles to work with as well as thermal
gradients for some temporary better snowfall rates in the broad
Midwest region. Obviously the low amplitude and speedy movement of
these systems makes them difficult to place and time in the
extended. Overall, the forecast thoughts and adjustments to the
National Blend of Models (NBM) were similar to the previous few
shifts.
On Friday, 1035-1038 mb high pressure will centered over the area
to start with a cold morning as a result and then only recovering
to the upper teens to mid 20s in the afternoon. With potential
southern Lake Michigan meso-low possibly still lurking near the
extreme northwest Indiana and immediate Illinois shoreline, have
a chance for flurries and slight snow shower chance mentioned. The
high pressure will exit southeast Friday night, resulting in
gradually increasing southerly winds and temperatures flatlining
or slowly rising.
The first disturbance we`re watching on Saturday is along/ahead
of a cold front packing a reinforcing surge of cold air. Limited
moisture and light QPF output on the guidance but decent forcing
with lift temporarily aligned with DGZ saturation amidst cold
advection could squeeze out a dusting to a few tenths of snow,
which we`re messaging in the grids as a chance of of light snow.
Breezy southwest winds ahead of the front will make for a
"milder" Saturday topping out in the upper 20s to lower 30s.
The "clipper highway" or "clipper train" pattern will feature
24-36 hour intervals of these systems moving into the broader mid-
upper MS Valley/western Great Lakes region. 500 mb ensemble mean
shows the core of the strongest 500 mb winds oriented toward our
general direction. Predictability is still low on the specifics
of these low amplitude disturbances several days out, but what we
can say is regular chances of light to moderate snow accumulations
are possible, depending on the tracks each individual clipper
takes.
There is a coherent signal for the next, stronger clipper on
Sunday among the 12z operational models, along with a weak surface
low reflection passing to our southwest and south. Looking at the
ensemble members, there is plenty of spread as is to be expected,
but with consistent enough signal the past few cycles, adjusted
PoPs up to mid chance range. Current timing favors Sunday morning
for most areas for threat of light snow accumulation and slippery
travel. Forecast soundings show a deep DGZ, so if lift is aligned
with DGZ, could see temporary moderate rates of fluffy/high ratio
snow.
The next clipper threat will follow closely on the heels of
Sunday`s wave. There is a good signal for Monday or later Monday
into Tuesday but very large ensemble member spread in short-wave
trajectory and timing. Monday daytime is currently favored for
the mid chance PoPs I-80 and north, with lower PoPs through Monday
night. At the end of the period, there is a strong signal at this
lead time for another shot of Arctic air driven in ahead of
incoming ~1040 mb high pressure. Exactly how cold it gets will be
determined by the snow cover extent. At the least in this set-
up, expect the lake effect machine to reinvigorate. Should a
southern stream wave and surface low track off to our northeast as
shown by a few guidance members, this scenario could even threaten
the Illinois side with lake effect snow Tuesday into Wednesday.
For now, have adjusted to low chance PoPs for the Illinois shore
and far northwest Indiana.
Castro/MTF
&&
.AVIATION...
For the 00Z TAFs...
There are no major aviation concerns through the next 24 to 30
hours. All terminals will remain largely cloud-free with north to
northwest winds gradually decreasing in magnitude through the
TAF period. Aircraft arriving or departing toward the east may
encounter icing while flying through a lake-effect stratocumulus
deck over Lake Michigan. Such lake effect snow showers (and
associated MVFR stratocumulus clouds) may occasionally get within
10 miles of GYY through the next 18 to 24 hours but the majority
of activity is expected to remain to the east. The wind direction
at ORD/MDW may attempt to flop north to northeasterly 21-00Z
tomorrow as a surface high pressure system approaches from the
northwest, though wind speeds are expected to be at or below 8kt
(if not lower) should such a change in direction occur.
Borchardt
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Winter Weather Advisory...INZ002 until 6 PM Thursday.
LM...Heavy Freezing Spray Warning...Winthrop Harbor to Burns Harbor
until 9 AM Thursday.
Small Craft Advisory...IL nearshore waters until 9 AM Thursday.
Small Craft Advisory...IN nearshore waters until 6 PM Thursday.
&&
$$
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