621
FXUS63 KILX 011916
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
216 PM CDT Sat Nov 1 2025

.KEY MESSAGES...

- Light scattered showers will continue this afternoon, mainly
  west of I-55 or south of I-70. Some of the showers west of I-55
  could contain graupel (small, soft hail).

- There is a 20-30% chance for fog west of I-55 early Sunday
  morning. With low temperatures below freezing, if fog does occur
  it could result in slick spots on elevated surfaces (such as
  bridges).

- The next chance for widespread rainfall is Thursday night into
  Friday as a cold front moves through the region. However, the
  probability of over a half inch of rain is just 10-20%.

&&

.DISCUSSION...
Issued at 207 PM CDT Sat Nov 1 2025

*** THROUGH TONIGHT ***

The short term forecast is largely evolving as anticipated, with
an upper low located immediately NW of the ILX CWA as of
130pm/1830z. This low will continue to pivot through the region
this afternoon. Made a minor increase to PoPs to closer to 30% in
areas to the west/south of Lincoln based on current radar trends.
mPING reports from Iowa, north MO, and NW IL are a mix of rain,
drizzle, and graupel, which is to be expected given model
soundings for this afternoon depicting dry low levels beneath the
cloud base and shallow, weak instability above the cloud base
(owing to steep mid- level lapse rates). While the gridded
forecast only mentions rain, it would not be a surprise if graupel
was observed within our CWA as well.

Another low probability aspect of the forecast to mention for this
afternoon is the potential for cold air funnels. The coolest temps
associated with the upper low are around -12 degC at 700mb and
-30 degC at 500mb, which is producing those aforementioned steep
mid- level lapse rates. Based on RAP-based vorticity fields, these
would be more likely west of I-55, which makes sense given the
closer proximity to the upper low. However, I suspect that
widespread cloud cover west of I-55 this morning (and into the
afternoon) will help limit the potential to some degree. The RAP
non-supercell tornado (NST) parameter (which includes several
ingredients supportive of cold air funnels) does show non-zero
(but very low) values west of the IL River this afternoon.

A cool night is expected this evening, with lows favored to fall
below freezing in most locations north of I-70 (40-60%). The main
source of uncertainty is the cloud cover, which based on current
satellite imagery extends well upstream of the upper low (cloudy
skies back into the Dakotas as of this writing). Much of the
diurnally-driven Cu should fade off after sunset though. If
clearing is more aggressive than currently forecast, lows could
wind up being several degrees cooler than currently forecast (the
mostly clear HRRR drops lows into the mid 20s), and fog could also
be an issue. Winds are expected to be light (less than 5 mph) as
a broad sfc ridge settles across the Midwest. Current NBM guidance
has just a 30% chance for visbys below 5 miles, while the HREF is
a bit more aggressive with a 30% chance for visbys below 1 mile
west of I-55. The concern here is that the scenario that is more
favorable for fog (less cloud cover) is also more favorable for
temps in the mid 20s, so if fog does form and is persistent at a
given location it could result in slick spots tomorrow morning.
The joint probability of both temps below freezing and visibility
below a half mile is 20-30% west of I-55 (and near zero to the
east).

*** SUNDAY INTO NEXT WEEK ***

There were no major changes to the extended forecast period at
this time. Sfc high pressure will settle over the TN Valley/SE US
through Tues, resulting in southwesterly sfc flow locally that
gradually warms temperatures above normal, into the mid 60s by
Tues.

Those above normal temperatures remain in place for much of the
week, with our next potential rainmaker expected late in the week
as a sfc low tracks across the upper Midwest to the north of the
ILX CWA. With persistent southerly flow ahead of that system,
seasonably mild lows are forecast Thurs night (near 50 degrees).
Unfortunately, the rainfall associated with this system looks
unlikely to put a meaningful dent in the drought, with just a
10-20% chance for over 0.50" of rain per the latest NBM. Will
need to monitor the diurnal timing of that front, as deep layer
shear values of over 40 knots could support a conditional severe
storm threat on Friday (high shear low CAPE).

Erwin

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1210 PM CDT Sat Nov 1 2025

An upper disturbance will move directly across the region this
afternoon, resulting in mostly cloudy skies. VFR ceilings are
favored, but some MVFR cloud decks have been observed and will be
possible this afternoon, primarily during the first few hours of
the period. A few light showers are also possible, mainly west of
I-55.

Tonight, some models are showing patchy fog. There was not enough
confidence on the location/coverage to be overly aggressive in the
TAF. Fog is most likely in areas west of I-55 (KPIA/KSPI),
introduced a 5SM BR at those sites Sunday morning. With temps
expected to be near or below freezing, there is potential for
freezing fog to produce slick spots. However, this would require
the fog being more widespread and thicker than currently forecast.
For now, probabilistic guidance has just a 20-40% chance of vis
below 3 miles.

Erwin

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$