Ice Storm and Winter Storm in Illinois, January 5 to 6, 2025

Area Forecast Discussion
National Weather Service Paducah KY
1058 PM CST Sat Jan 4 2025

.KEY MESSAGES...

- A major winter storm remains on track to impact the region
  tonight through Monday morning. A Winter Storm Warning, Ice
  Storm Warning and Winter Weather Advisory have all been
  issued. The greatest uncertainty remains on the border of the
  Ice Storm Warning and Winter Weather Advisory.

- Damaging ice impacts are likely and will lead to disruptive
  travel delays and scattered power outages. Significant ice,
  sleet and snow accumulations are all expected.

- The coldest air of the season so far remains on track to
  settle over the region next week. Temperatures will struggle
  to rise above freezing until Friday, with wind chill values
  falling into the single digits, and at times below zero. Any
  prolonged power outages will make this arctic blast more
  dangerous.

&&

.DISCUSSION...
Issued at 250 PM CST Sat Jan 4 2025

A major mixed precipitation winter storm remains in the
forecast tonight through Monday morning, producing a mix of
snow, sleet, and freezing rain. Warning/advisory products have
been adjusted to have the same start/end times of 2am Sunday to
6am Monday, with the Winter Storm Warning in the northern third,
an Ice Storm Warning in the middle third, and a Winter Weather
Advisory in the southern third of the Quad State region.

On the synoptic scale, this system is a shortwave trough
presently located over the Rockies. High pressure is located
over the Southeastern CONUS. This shortwave system strengthens
rapidly as it emerges into the Central Plains with the surface
low pushing eastward near the KY/TN border by Sunday evening as
the surface cold front pushes heavy rain through Western
Kentucky. There is a very slight lingering southward lean in
the ECMWF/CMC.

Models suggest a slightly earlier start to precipitation, though
an initially dry surface layer will take some time to moisten to
have precipitation reach the ground. 12Z CAMs have increased
precip into the Bootheel late tonight, which should fall mainly
as rain. As moderate precipitation moves in further north, a
primarily snow/sleet mix is expected in the north, with a more
prominent band of freezing rain from the Ozark Foothills through
Cape Girardeau, Missouri, eastward to Carbondale and Harrisburg
in Southern Illinois, to near the Evansville Tri-State. The
northern half to two-thirds of the Quad State will struggle to
reach freezing as northeasterly winds maintain lower dew points.
The forecast continues the strategy used by the previous shift
of blending in NBM 50th percentile temps to lower temperatures
a little to maintain wet-bulbing.

The warm frontal progression northwards will be key to
delineating heavy ice accumulations. Confidence in the
snow/sleet mix is highest along the I-64 corridor with 2-4
inches of combined snow/sleet likely. Freezing rain is likely to
mix in with the limited Sunday afternoon warming when the
surface refreezing layer diminishes. Freezing rain totals up to
around a quarter of an inch are possible. A Winter Storm Warning
is used to cover this primarily snow/sleet region.

The highest concern is in the Ice Storm Warning zone from Cape
Girardeau through northwestern Kentucky where widespread half
inch with localized three-quarters of an inch of ice accretion
is forecast with a bit higher confidence in sustaining freezing
rain longer in the western half of the Ice Storm Warning area.
This will swiftly make any travel treacherous. Heavier
precipitation rates will reduce ice accretion potential on trees
and power lines, but breezy winds of 10-20 mph and gusts of
20-25 mph during the afternoon is a point in favor of line ice
accretion rates. With wet soils, breezy winds, and significant
ice accretion, tree and power line damage is likely in the Ice
Storm Warning area with scattered power outages. This ice event
will not have the totals or multi-round effects of the 2009
Western Kentucky Ice Storm, but has potential to be the most
impactful ice event for the Quad State since that historic
storm.

The southern two rows of counties with the Winter Weather
Advisory have a complex timeline which has resulted in extending
the advisory to 6am Monday. Freezing rain will cause
significant travel impacts for the morning, with an abrupt
transition from very little ice to significant icing expected
from south to north. Caution should be maintained even if icing
appears minimal. A transition to rain is expected during the
afternoon hours, potentially clearing up morning ice cover.
Following the evening cold frontal passage, model soundings
indicate a dry layer in the dendritic growth zone (DGZ) during
the evening into the overnight hours which could lead to a
transition to freezing drizzle Sunday night, prompting the
extension of the Advisory.

The freezing drizzle potential across the entire Quad State
Sunday evening/overnight will bring varied hazards. In the
north, gusty winds and ongoing ice on trees and power lines will
very efficiently accrete any freezing drizzle that does occur.
At the surface, in the north, freezing drizzle will just add a
solid layer to the top of the snow/sleet/ice. In the south,
freezing drizzle on rain-cleared roads could quickly develop
black ice, making travel more dangerous than it would otherwise
appear. Late Sunday night, moistening of the DGZ will lead to a
transition to light snow that continues into Monday morning with
an additional half inch or so of snow possible, which may cover
a more hazardous sub-layer of ice.

Forecast temperatures through this event remain very close to
the previous forecast, which has kept snow/sleet and ice
accumulations fairly close to the prior run. However, slight
adjustments, especially to the 32F line, will have significant
impacts. The greatest uncertainty lies in the transition zone
from the Winter Weather Advisory to the Ice Storm Warning.

Colder air surges into the Quad State following this storm, and
any areas with snow/ice cover will see further radiative
cooling. Temperatures remain below freezing for all but the
southernmost areas through the week, with melting limited to
solar radiation during the day as skies become more sunny
midweek. Low temperatures fall to the single digits Tuesday
night, and near 0 along the I-64 corridor Wednesday night. Wind
chills in the single digits are likely in northern areas early
morning Monday and Tuesday, and wind chills of -5 to 5 across
the Quad State Wednesday morning. Any sustained power outages
would exacerbate cold weather concerns.

Ridging keeps conditions dry midweek, with a deep trough
developing for late week, bringing a potential round of snow
for the end of the week. NBM PoPs seem low at this time, but
with the high priority near term event, will refrain from making
any large adjustments to day 7 for now.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1042 PM CST Sat Jan 4 2025

Little changes from the previous TAF discussion. Starting to see
radar echoes across the terminals this evening and already are
starting to get a few reports of sleet and snow. Most of the
activity will move in from the west over the coming hours. Cigs
will gradually lower throughout the night with MVFR expected at
all sites by the morning. Further reductions in cigs and visby
is expected with IFR or LIFR conditions at times. Precipitation
type transitions still a bit uncertain with more sleet and snow
across the northern terminals and more freezing rain across the
southern terminals. By the afternoon, temperatures warm above
freezing at PAH/CGI for a transition to rain showers.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Warning from 2 AM Sunday to 6 AM CST Monday for
     ILZ075>078-080>083.
     Ice Storm Warning from 2 AM Sunday to 6 AM CST Monday for
     ILZ084>094.
MO...Ice Storm Warning from 2 AM Sunday to 6 AM CST Monday for
     MOZ076-086-087-100-107-111.
     Winter Weather Advisory from 2 AM Sunday to 6 AM CST Monday
     for MOZ108>110-112-114.
IN...Winter Storm Warning from 2 AM CST /3 AM EST/ Sunday to 6 AM
     CST /7 AM EST/ Monday for INZ081-082-085>088.
KY...Ice Storm Warning from 2 AM Sunday to 6 AM CST Monday for
     KYZ007-010-013>016-018>020.
     Winter Weather Advisory from 2 AM Sunday to 6 AM CST Monday
     for KYZ001>006-008-009-011-012-017-021-022.

&&

DISCUSSION...ATL
AVIATION...AD

Hazardous Weather Outlook
National Weather Service Paducah KY
411 AM CST Sat Jan 4 2025

ILZ075>078-080>094-INZ081-082-085>088-KYZ001>022-MOZ076-086-087-
100-107>112-114-051015-
Jefferson-Wayne IL-Edwards-Wabash-Perry IL-Franklin-Hamilton-
White-Jackson-Williamson-Saline-Gallatin-Union-Johnson-Pope-
Hardin-Alexander-Pulaski-Massac-Gibson-Pike-Posey-Vanderburgh-
Warrick-Spencer-Fulton-Hickman-Carlisle-Ballard-McCracken-Graves-
Livingston-Marshall-Calloway-Crittenden-Lyon-Trigg-Caldwell-
Union KY-Webster-Hopkins-Christian-Henderson-Daviess-McLean-
Muhlenberg-Todd-Perry MO-Bollinger-Cape Girardeau-Wayne MO-Carter-
Ripley-Butler-Stoddard-Scott-Mississippi-New Madrid-
411 AM CST Sat Jan 4 2025 /511 AM EST Sat Jan 4 2025/

This Hazardous Weather Outlook is for portions of southern
Illinois, southwest Indiana, western Kentucky, and southeast
Missouri.

.DAY ONE...Today and Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

An Ice Storm Warning, Winter Storm Warning and Winter Weather
Advisory have been issued across the region. Significant
accumulations of freezing rain, sleet, and snow are expected
beginning early Sunday morning. Travel will likely become
hazardous and power outages will be possible. Farther south, some
brief travel difficulties will be possible at the onset of the
precipitation until temperatures climb above freezing Sunday
morning. Refer to each product for more details.

An extended period of sub-freezing conditions is expected from
Monday through at least Thursday. The coldest conditions are
expected Tuesday night and Wednesday night, when wind chill values
will range from the single digits below zero in the north to the
single digits above zero in the south.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

DW