Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/15/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 852 PM CST Fri Jan 14 2022

.UPDATE...
Issued at 852 PM CST Fri Jan 14 2022

Main change for tonight was to keep likely pops going longer and
for more of the area. For the most part, the snow flakes have
been very tiny but the flake size does increase some with the
higher reflectivity, currently near the lake and in northwest IN.
This very light snow will continue for several hours as it begins
to diminish from north to south in the early morning hours and
adjusted pops accordingly. Some lake effect flurries or snow
showers may continue near the lake through and possibly after
daybreak. Low confidence for this and made no changes to the
current slight chance pops. Snow amounts should generally be
under one inch, though there may be some isolated higher amounts
near the lake, as well as across the far western cwa.

Late this afternoon, there was quite a bit of drizzle and
freezing drizzle across northwest IN and while the main roads
were generally wet, some icing likely did occur on untreated
surfaces. With temps slowly dropping, any untreated surfaces
across northwest IN may have a light glaze from this earlier
drizzle, which will now get coated with the light snow. cms

&&

.SHORT TERM...
Issued at 200 PM CST Fri Jan 14 2022

Through Saturday night...

A large system of snow is enclosing on the CWA from the west
having already introduced some flurries to parts of north-
central IL. This snow will continue to inch toward the Chicago
metro through the remainder of the afternoon. Snow from this
system will be in the area through the rest of the day and most of
tonight before retreating to the south before daybreak tomorrow.
Snow rates should vary between 0.1 to 0.2"/hr, especially west of
I-39 where noticeably reduced visibilities and slick (rural) roads
are a distinct threat. This is where we`ll see the heaviest snow
come down over the next several hours and where we see the best
chance for snow totals in excess of one inch. The majority of the
Chicago metro area should see totals around or under an inch while
areas east of I-55 may not see any more than a light dusting as a
result of this system.

Persistent onshore flow also presents the chance for some plumes of
lake-effect snow later today. As the temperature contrast between
the lake and the air moving over it grows this evening, so does our
potential for seeing some lake-induced snow flurries. The greatest
chance for lake-effect snow appears to be late this evening and
through the night although we could potentially continue to see
flurries come off of the lake as late as the early afternoon
tomorrow. Coverage in lake-effect snow should be mostly restricted
to counties situated along the lake although areas such as DuPage,
eastern McHenry, and eastern Will Counties could be an exception.
Relatively low lake-induced ELs of 5000 kft or so should hold the
snow intensity low and likely non-accumulating beyond the "system"
snow.

In other news, temperatures this evening and overnight should be
slow to cool and most areas will find it hard to drop below 20
degrees for a morning low tomorrow thanks to cloud cover keeping
us nice and insulated. Winds gusting upwards of 20-25 mph
however will pull wind chills down into the single digits for
most by early tomorrow morning. Temperatures will warm into the
mid-20s tomorrow afternoon but continued breezy conditions will
keep wind chills in the teens. Winds will subside through the
evening tomorrow with a system of high pressure dropping down from
the north, allowing for lows to drop into the lower teens
areawide.

Doom

&&

.LONG TERM...
Issued at 126 PM CST Fri Jan 14 2022

Sunday through Friday...

After a chilly start, Sunday will feature increasing clouds and
highs in the low to mid 20s. A quickly-moving upper-level
shortwave and associated surface cold front will dive south across
the Great Lakes after sunset leading to a brief shot of breezy
northwesterly winds. While the upper-level lift afforded by DCVA
and temperature profile will be supportive of a band of snow
along and behind the front, BUFKIT overviews signal that a stout
layer of dry air from the surface to about 10kft may chew
everything up into virga. Even so, a majority of EPS ensemble
members continue to produce a trace of precipitation which usually
verifies as flurries. For now, will maintain low-end PoPs in
anticipation for flurries and perhaps a brief non-impactful, non-
accumulation snow shower overnight into Monday.

Monday itself and Tuesday look pleasant with warming temperatures.
Tuesday will probably be the warmest day of the workweek as
southerly winds help boost highs into the mid 30s. Wednesday, an
arctic cold front will sweep through the Lower Great Lakes leading
to falling temperatures and breezy northwest winds. Lows Thursday
and Friday mornings look to return to the single digits with wind
chills below zero. Highs Thursday and Friday will climb into the
teens to around 20. All areas look to remain dry from the middle
of the week onward, except perhaps across far northeastern Porter
County where occasional lake effect snow showers may sneak in from
La Porte county.

Borchardt

&&

.AVIATION...
For the 00Z TAFs...

Aviation Forecast Concerns:

* Light snow with MVFR/occasionally IFR conditions tonight. Some
  patchy freezing drizzle at GYY very early this evening.

* MVFR ceilings linger into Saturday, with some light lake effect
  snow showers or flurries at times through midday.

* Blustery northeast winds with gusts around 20 kt tonight into
  early Saturday.

Surface low pressure was over north Texas early this evening, with
a trough extending northward into the mid-Missouri Valley in
association with a pair of mid-level disturbances tracking
southeast across the region. To the east/northeast of this area of
surface low pressure, blustery northeast winds were in place
across the western Great Lakes, and these are expected to continue
overnight and Saturday morning before gradually diminishing and
eventually turning east-southeast Saturday evening. Sustained
speeds 12-15 kts and gusts around and at times a little above 20
kts are expected.

Regional radar mosaics indicate an area of moderate to heavy snow
to our west across IA and far western IL, and this area of
precipitation will continue to develop southeastward across MO,
western and southwestern IL through early Saturday. Locally, the
terminals will be within lighter snow within the eastern periphery
of this activity this evening, with snow eventually tapering after
midnight. Earlier AMDAR aircraft soundings had depicted a
pronounced dry layer roughly between 7000-13000 feet AGL which
took some work to saturate, though light snow has been reported at
both ORD and MDW in the last hour or so and recent soundings
indicate this dry layer is saturating. In addition, precip from
higher levels may be seeding the moist low level layer coming off
the lake which has led to some recent radar reflectivity increases
across the Chicago metro/Lake Michigan area. This in general
suggest snow should be filling in with MVFR/IFR visibilities
becoming more common early this evening as light snow persists.
Models suggest light snow associated with the system to our west
should ease around/shortly after midnight. With persistent
northeast flow off the lake however, expect that some lighter snow
showers or just flurries will persist into Saturday morning.
Forecast soundings depict rather shallow inversion layers not very
impressive for anything significant, but some flakes will likely
be around at times for the metro locations. Gradual weakening and
veering of the low level flow should make conditions less
conducive to lake effect Saturday afternoon/evening, with
ceilings expected to improve to VFR late in the day/evening.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...IL nearshore waters until 6 PM Saturday.

     Small Craft Advisory...LMZ743-LMZ744 until 3 PM Saturday.

     Small Craft Advisory...Burns Harbor to Michigan City IN until 3
     AM Saturday.

&&

$$

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Area Forecast Discussion...Updated Aviation

National Weather Service Saint Louis MO

 600 PM CST Fri Jan 14 2022

.SHORT TERM...  (Through Late Saturday Night)
Issued at 246 PM CST Fri Jan 14 2022

We are still looking at our first widespread snowfall for the area
tonight into Saturday morning. The main changes/concerns are we will
see more rain at the onset before a transition to snow, and this
transition will not be uniform across the CWA.

The overall set-up hasn`t changed drastically. An upper trof/low
currently centered in the north central Plains will dig southward
through the Plains tonight. Increasing large scale forcing
associated with the upper trof (which is a bit greater now), good
mid level frontogenetical forcing, isentropic lift, and divergence
aloft associated with the ULJ and decreasing wavelength will result
in an increasing and large area of precipitation/snow. This area
of snow will be anchored by a robust and wide west/northwest-
east/southeast band associated with the strong frontogenesis and
mid level lapse rates of 6-6.5 degC/km. This band should start
poking into northeast MO later this afternoon with the precipitation
really expanding this evening, and then gradually transitioning
southward overnight as the upper trof and forcing shift
southward.

Temperatures have gotten a bit warmer than expected today and
this will result in a slower changeover from rain to snow. The
changeover won`t be uniform owing to precipitation intensity and
ability to cool the low levels. It will take longer in central and
southeast MO, predominately overnight. The changeover should
occur sooner across northeast and east-central MO into western IL
where the more robust band with higher precipitation rates is
expected. Several recent AMDAR soundings with ascents out of
Lambert International are showing the warm layer aloft extends to
a height of about 850 mb, however the overall magnitude is not
very strong with temps below 1 degC, and this should be eroded
once the precipitation and intensity ramps up. Current thinking in
the St. Louis region is from around 02-04z.

This will be a wet snow and will accumulate and compact. At times
snowfall rates will be from 0.5-1.0 per/hr contributing to
accumulation on roadways and deteriorating driving conditions. We
are still thinking that northeast MO and west central IL will see
the highest totals owing to longevity and intensity with 6+ inches
possible, while much of the remainder of the region will be in
the 3- 5 inch range. South central IL will see the least snowfall.


Current thinking is the snow will wind down pretty quickly between
15-18z on Saturday and may completely end by early afternoon across
the far southern CWA as the forcing shifts southward attendant with
the digging upper trof/low.

There has been little change to the headlines other than to start
and end some of the advisories sooner.

The trend in the latest ensemble and deterministic models still has
the upper low digging southeast through the southern Plains and
lower MS Valley on Saturday night and bottoming out in the Deep
South on Sunday morning. This track would continue to suggest that
additional snow Saturday night with the deepening mid-latitude
will remain south of the CWA.

Glass

.LONG TERM...  (Sunday through Next Friday)
Issued at 246 PM CST Fri Jan 14 2022

The latest model guidance continues to show a fast-moving short wave
trof moving through the region on Sunday night. At its least this
trof should bring a reinforcing shot of colder air to the region.
We`ve had an eye on this wave for bringing a shot of light snow to
the area, especially from northeast MO/west central IL sewd through
south central IL. Previously just the operational ECMWF and a few of
the EPS members were indicating this potential, but now a few more
models are suggestive. At this point we will continue to monitor
this time frame and see how the guidance trends. This would be a
rather light event if we see anything, with amounts with less than
an inch and possibly not much more than a good dusting.

Monday still looks like a seasonably cold day with weak high
pressure settling into the area. Present indications support
previous thinking we will see a brief warm-up on Tuesday with
heights aloft rising and low level WAA setting up. However as I have
alluded to the last few days, snow cover will likely temper the
magnitude.

Heading into mid-late week, we begin to see lowering heights aloft
as a broad upper trof evolves across NOAM. An initial short wave
associated with this evolution is expected to send a cold front
through the region on Tuesday night. A rather impressive and cold
1040+ mb surface high will build southeastward into the region in
the wake of the cold fropa. While there is some spread in the
magnitude of the cold air, the air mass looks pretty cold and
snow cover to our north will help in that respect, and
temperatures will certainly be well below normal.

Glass

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 600 PM CST Fri Jan 14 2022

Flight conditions will deteriorate through the evening as a winter
storm arrives across the region. As precip continues to develop and
overspread the region, flight conditions are expected to deteriorate
to LIFR/IFR at all terminals. Precip will begin as a period of
rain/drizzle mixed with snow, before eventually changing to all snow
as precip intensity increases along a band of snow forecast to form
across northeastern MO/west-central IL and drift southward through
the evening and overnight. Depending on where this band sets up,
higher snowfall rates could result in visibilities lower than 1 SM.
After 12z Saturday, snow should begin to move out of the region from
north to south and be south of all terminals by 18z. However, IFR
stratus will prevail through most of the day Saturday. Improvement
in flight conditions is anticipated Saturday evening as stratus
scatters/clears upon arrival of drier air, with VFR flight
conditions possible beyond 00z Sunday.

Pfahler

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory from midnight tonight to 6 PM CST
     Saturday for Crawford MO-Iron MO-Madison MO-Reynolds MO-
     Saint Francois MO-Sainte Genevieve MO-Washington MO.

     Winter Weather Advisory until noon CST Saturday for Lincoln MO.

     Winter Weather Advisory from midnight tonight to noon CST
     Saturday for Audrain MO-Boone MO-Callaway MO-Cole MO-
     Gasconade MO-Moniteau MO-Montgomery MO-Osage MO.

     Winter Weather Advisory from 9 PM this evening to noon CST
     Saturday for Franklin MO-Jefferson MO-Saint Charles MO-
     Saint Louis City MO-Saint Louis MO-Warren MO.

     Winter Storm Warning until noon CST Saturday for Knox MO-Lewis
     MO-Marion MO-Monroe MO-Pike MO-Ralls MO-Shelby MO.

IL...Winter Weather Advisory from midnight tonight to 6 PM CST
     Saturday for Randolph IL.

     Winter Weather Advisory until noon CST Saturday for Bond IL-
     Calhoun IL-Greene IL-Jersey IL-Macoupin IL-Madison IL-
     Montgomery IL.

     Winter Weather Advisory from 9 PM this evening to noon CST
     Saturday for Clinton IL-Monroe IL-Saint Clair-Washington IL.

     Winter Storm Warning until noon CST Saturday for Adams IL-Brown
     IL-Pike IL.

&&

$$

WFO LSX



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