Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/17/23

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 545 PM CST Mon Jan 16 2023

.SHORT TERM...
Issued at 251 PM CST Mon Jan 16 2023

Through Tuesday night...

An area of showers continues to move through northeastern Illinois
and northwest Indiana ahead of a warm front that is currently being
analyzed along a Sterling, IL to Pontiac, IL line. While some of
these showers have shown signs of vertical development on radar,
they have struggled to produce any lightning recently. The reason
for the lack of lightning so far is likely due the low topped
nature of these more robust showers (tops under 16,000 ft) and
lack of surface based instability as noted on recent aircraft
soundings out of MDW. However, the aircraft and forecast soundings
are still showing mid-level lapse rates on the order of 6 to 7
C/km which is sufficient to support some convective development
and the chance of an isolated lightning strike or two as these
showers continue to move northeastward towards the open waters of
Lake Michigan over the next hour or two.

The warm front will continue to lift northward through northeastern
Illinois this evening as the 993 mb surface low currently over
central Iowa continues to move northeastward into southern Wisconsin
which will drag a cold front through the area this evening. As this
occurs dew points are expected to continue to increase into the
upper 40s with a couple locations possibly seeing 50 degree dew
points in our far southern CWA which will set the stage for the
development of additional showers and possibly a few thunderstorms
through this evening. While the increasing dew points will allow for
some destabilization (MUCAPE values of a few hundred J/kg) forecast
soundings continue to indicate that this instability should remain
elevated. Regardless, forecast soundings are also showing decent
shear profiles in place in the warm sector this evening which could
allow for some thunderstorms to become better organized and possibly
contain a marginal threat for some small hail and gusty winds. There
is also the very small chance (less than 2%) that a brief spin up
could occur if some surface based instability can be realized. Again
this potential is very low, but is something worth keeping an eye on
through this evening especially across our southern CWA where
forecast soundings show some slightly better chances for surface
based instability. Any already low severe risk will end by about 8
PM as nocturnal CIN increases. Any showers and/or storms that do
develop this evening should move out of the area around midnight
with the cold front.

Otherwise, expect mostly cloudy skies and breezy conditions to
persist through Tuesday evening. Winds will become westerly
overnight behind the aforementioned cold front with gusts in the 25
to 30 mph range returning Tuesday afternoon. Temperatures will also
continue to warm through this evening with highs looking to top out
in the mid to upper 40s to near 50 by midnight tonight. Tuesday`s
high is expected to occur shortly after midnight with temperatures
gradually diminishing through the day before settling into the low
to mid 30s Tuesday night.

Yack

&&

.LONG TERM...
Issued at 148 PM CST Mon Jan 16 2023

Wednesday through Monday...

We continue to focus in on the Wednesday evening and Thursday
time frame in the extended portion of the forecast as a secondary,
robust storm system spreads across the central plains and Upper
Midwest. While minor run-to-run wobbles in the storm track
continue, overall variability has diminished, with model guidance
looking like it`s settling on a more stable solution. This now
takes the parent 850 mb low track along a roughly Kansas City to
Milwaukee line (and even some suggesting farther north and west
than that) and is one that climatologically is very difficult to
realize significant snow amounts for our forecast area.

The initiating impulse for this next system is presently just off
the NorCal coast, and this will swing east across the Sonora
Desert before ejecting out across the plains on Tuesday night. As
this occurs, rapid lee cyclogenesis will take place across the
OK/TX Panhandles under an increasingly divergent upper jet. A
robust warm advection wing will materialize, shuttling a mild
(for January standards) airmass across much of our region, with
850 mb temperatures now forecast to rise into the 0 to +5 C region
through Wednesday. The sharpening baroclinic zone will end up
focusing the northeastward advance of the surface low reflection.
In this scenario, pretty much wherever the 0 C low-level isotherm
sets up will be close to the southeast extent of the better
snowfall chances as a fairly potent 40 kt southeasterly low-level
jet focuses intense warm advection across the region. There still
seems to be some uncertainty exactly where this will set up, but
the multi-model/ensemble consensus today is for the most
appreciable snow chances to focus primarily into NE Iowa and
Wisconsin. Will note there remain some more southerly solutions
within the ensemble spread, and any subtle SE wobbles would bring
more of a wintry threat into our northern locales.

As it stands right now, thinking is that precipitation will begin
breaking out across our region through late Wednesday afternoon
and in the form of plain rain for areas south of about I-88, and a
mix (mainly rain though) to the north. Dynamic cooling will have
to fight with the aforementioned intense region of WAA, and given
how wound up things are, have a feeling the latter will end up
winning out with p-types eventually transitioning to primarily
rain across even our far northwest locales. In the intervening
hours on Wednesday evening before the LLJ really gets cranking,
however, do see a brief window where a burst of all snow could be
realized over the very far NW reaches of our CWA given the
presence of very steepened lapse rates above about 600 mb. The
12z UKMET highlights the results of this instability and strong
forcing acting on a slightly colder column, with a burst of quite
heavy snow occurring for a brief period Wednesday night. Something
we`ll have to keep an eye on with any subtle SE shifts, but this
is presently within the outlier portion of the multi-model
envelope right now.

General neutral tilt to the parent trough axis will not provide
any counter to the rapidly-advancing dryslot which looks to blast
through our region by early Thursday morning (quite the change
from a few days ago). As a result, even where it is still snowing,
things will quickly transition to drizzle or very poor-quality/low
ratio snow. Do not have drizzle formally reflected in the grids
right now, but temperatures will likely be above freezing meaning
any lingering travel impacts should ease through the AM.

The core of the main upper low will pass overhead through
Thursday morning. Very cold temps aloft will drive decent elevated
instability--sufficient for the development of scattered rain and
snow showers.

The next chance for any wintry precipitation appears to be in the
Sunday-Monday time frame as another series of intermingling
northern and southern stream waves transit the region. Quite a bit
of uncertainty regarding phasing, forward speed, and moisture
content at this point, so made no alterations to the blended
slight chance PoPs during this period.

Carlaw

&&

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

IFR/LIFR CIGS along with -DZ/BR and IFR/MVFR VIS expected this
evening ahead of an approaching cold front. Behind the cold front,
look for a short window of VFR conditions before lower end MVFR
CIGS move back in overnight, likely eventually lowering to IFR
late tonight or early Tuesday morning. IFR/low end MVFR stratus
appears likely to remain locked in Tuesday into Tuesday night.

South winds this evening will become southwest behind the front
and likely become gusty later tonight into Tuesday, eventually
veering more westerly Tuesday.

- Izzi

&&

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

     Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...9 AM Tuesday to 9 PM Tuesday.

&&

$$

Visit us at weather.gov/chicago

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSChicago
www.twitter.com/NWSChicago
www.youtube.com/NWSChicago