193
FXUS63 KILX 050904
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
304 AM CST Wed Feb 5 2025

.KEY MESSAGES...

- There is a 60-80% chance for freezing rain north of roughly
  I-70 today. South of roughly I-72, this should change to plain
  rain during the afternoon, but further north the freezing rain
  may continue through the evening.

- While ice accumulations will be light, slick pavement will
  increase the risk for automobile collisions and pedestrian
  falls.

- Another storm system will bring precipitation to the area
  Friday night into Saturday. There is a 20-40% chance this will
  fall as freezing rain, highest chances north of roughly I-72.

&&

.DISCUSSION...
Issued at 256 AM CST Wed Feb 5 2025

*** FREEZING PRECIP TODAY ***

At 3am, water vapor satellite imagery indicated a broad area of west-
southwesterly moisture transport across the Plains and Midwest ahead
of a large trough lifting across the PacNW and Great Basin. The ILX
vad profiler reveals a sharp veering of winds near a temperature
inversion around 1.5km AGL, with winds below that level blowing from
the east-northeast. Strengthened by a tight gradient stemming from
high pressure centered to our north, these low level winds continue
the steady importation of drier air into the region, maintaining 5-9
degF dewpoint depressions at the surface and the even drier layer
seen on our and DVN`s 00z raob`s at around 900-850mb. This will
continue serving to delay the onset of precipitation across our area
during the morning, though eventually the freezing rain (or, more
properly, "drizzle" if models are correct in suggesting little/no
cloud ice will be present) will reach us and pose a risk for travel
issues. Guidance continues to be divided on onset time, but in
general they`ve slowed down, having low level saturation (0-1km RH
>85%) arriving mid to late morning across our southwest counties to
early-mid afternoon near I-74. Uncertainty still surrounds the
location of the 32 degF isotherm during the afternoon, but CAMs
have trended a little south which seems reasonable given the
continued cool advection ahead of the precip, and the enhanced
evaporational cooling with it via dry air entrainment by the
aforementioned east-northeast winds. The estimated probability
for surface temps less than freezing (based on percentage of HREF
members) remains 60-70% or greater along and north I-74 all day,
while further south it bottoms out around 30-60% between 1 and 3
pm. In other words, our confidence is highest (60-80%) that
precipitation will fall as freezing rain/drizzle near and north of
I-74 during the afternoon and evening while further south it`s
more of a toss-up whether it`ll change to all rain or remain
frozen. The area should experience a surge of warmer temperatures
late evening into the overnight as winds veer to southerly, but by
this time precip will actually be ending. Taking all of this into
account, we elected to extend much of (roughly along and north of
the I-72 corridor) the advisory in time to give everyone as much
heads up as possible that the freezing rain may not switch over to
plain rain as early as we all hope; the next shift can always
cancel early if temperatures warm earlier than planned.


*** ANOTHER SYSTEM HEADING INTO THE WEEKEND ***

A transient shortwave ridge will cross the region in the wake of
that upper low tonight into early tomorrow, with a push of weak cool
advection behind an ill-defined cold front settling into the area
Thursday evening. As a result, high temperatures will exceed
climatological normal by about 10-15 degF (highest across our south)
tomorrow, the forecast featuring low-mid 40s north to mid-upper 50s
south. With cold advection in the wake of that front strengthening
across the area on Friday, temperatures will run a bit cooler and
closer to climatology for early February.

All attention then turns to the next weather-maker, which will
spread precip back across central and southeast IL beginning Friday
night. This feature is slated to take a similar track to today`s
storm, only forcing aloft is slightly stronger and most LREF members
have an actual surface low developing with this one which would
subsequently track near/through our neck of the woods.
Overrunning will once again result in thermal profiles suggestive
of either rain or freezing rain (depending on surface temps) for
most of central IL, though can`t completely rule out some snow on
the low`s backside if forcing for ascent is strong enough for a
TROWAL to develop (at this time, that seems unlikely). LREF
continues to advertise 40-60% chances for freezing rain north of
roughly I-72 Friday night into Saturday, while NBM chances are
closer to 15-30%. We`ll lean towards NBM given LREF`s wet bias
and call it 20-40% until details start to become more clear.

Because of uncertainty in the low`s track, confidence remains
likewise low in the temperature forecast Saturday - particularly
across our southern CWA. For example, the interquartile range
(IQR) for high temperatures in Mattoon spans 40-57 degF, meaning
the daily high temperature is as likely (50% chance) to verify
between these values as it is to verify outside them. Confidence
increases in the temperature forecast to close the upcoming
weekend, with Sunday`s highs unlikely (less than a 15% chance) to
exceed 40 near and north of roughly the I-70 corridor.

*** SEASONABLY COOL NEXT WEEK ***

While there`s a typical amount of spread in the LREF system heading
into next work week, the general trend is for seasonably cool
temperatures. There are some hints at snow Monday into Tuesday,
though most guidance keeps the heaviest precip south of us for now;
we`ll keep a careful eye on that.

Bumgardner

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1054 PM CST Tue Feb 4 2025

Northeast winds remain somewhat elevated late tonight with
occasional gusts to 20 kts. Winds will veer to the east by morning,
then south-southeast Wednesday evening. 4-6k ft stratus has
overspread the area late tonight with lower ceilings expected to
arrive during the day on Wednesday ahead of a wintry precipitation
event. Precipitation chances begin to increase from mid to late
morning in the south (KSPI, KDEC) and then by mid afternoon further
north at the remaining airfields. A mix of rain and freezing rain
will be the main precipitation types, with temperatures looking to
remain cool enough at northern airports to support the chance for
freezing rain/drizzle through the evening hours. IFR to LIFR
conditions make a push after 00Z, with patchy fog possible once
precipitation ends sometime after 06Z.

NMA

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon today to midnight CST tonight
for ILZ027>031-036>038-040-041.

Winter Weather Advisory from 6 AM this morning to 9 PM CST this
evening for ILZ042>051-053.

Winter Weather Advisory from 6 AM this morning to noon CST today
for ILZ052-054>057-061.

&&

$$