185
FXUS63 KILX 061821
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
121 PM CDT Wed May 6 2026

.KEY MESSAGES...

- Frost potential tonight...there is a 30 to 50% chance of
  conditions favoring frost formation north of I-70 late tonight
  with the highest probabilities near the I-74 corridor east of
  I-39.

- Thursday showers and gusty winds...Scattered (30-40%) showers
  and isolated (20%) storms are expected near the I-74 corridor
  Thursday afternoon and evening. Any storms are expected to
  remain sub-severe, but a few gusts of 30 to 40 mph are
  possible.

&&

.DISCUSSION...
Issued at 105 PM CDT Wed May 6 2026

Tonight: Frost Potential
The overarching pattern through Friday remains dominated by
upper-level troughing centered over the Great Lakes, driving a
period of below-normal temperatures and a couple of light
precipitation chances. At the surface, a 1020mb high pressure
system, initially over Kansas and Nebraska, will track east
across the mid Mississippi and lower Ohio Valleys overnight.

The main concern tonight is the potential for frost. A brief
window of favorable radiational cooling--clear skies and light
or calm winds--is expected as the ridge axis moves overhead.
This will allow temperatures to rapidly fall through the 40s,
with some spots dipping into the upper 30s. Mid-level warm air
advection will spread back across the region behind the ridge
axis, potentially leading to increasing cloud cover from the
west late tonight and helping temps level off.

The joint probability for temperatures below 38degF and cloud
cover less than 30% (the threshold favorable for frost
formation) ranges from 30-50% north of I-70, with the highest
probability along and north of the I-74 corridor east of I-39.
While confidence in widespread frost formation is currently too
low for a headline, we will continue to monitor the situation.
If confidence increases later this evening, a Frost Advisory may
be required.

Thursday and Friday: Scattered Showers/Storms
On Thursday, a series of low-amplitude shortwave troughs will
dig across northern Illinois, bringing a chance of scattered
showers and isolated thunderstorms to the region. Forecast
soundings show steep low and mid-level lapse rates (an inverted
`v` profile), which will efficiently mix down winds in any
convective precipitation. However, low equilibrium heights are
expected to limit the overall strength and depth of convection.
The latest 12Z HRRR model suggests the potential for gusts up to
around 30 knots within any showers or storms. PoPs are highest
(30-40%) along the I-74 corridor, with dry conditions becoming
favored further south.

A slightly deeper shortwave trough will dig across the region
on Friday, with a weak surface low reflection moving across
central Illinois Friday afternoon and evening. Instability is
expected to be quite limited due to poor mid-level lapse rates,
with pockets of MLCAPE peaking around 300-400 J/kg ahead of the
surface low. Meanwhile, deep layer shear will be moderately
strong, around 50 knots. Given the modest synoptic-scale forcing
and generally weak instability, convection is currently
expected to remain sub-severe on Friday.

Weekend Forecast: Brief Warmup Followed by a Strong Front
The upper trough will briefly retreat on Saturday as shortwave
ridging moves overhead, setting the stage for a dry start to the
weekend. Temperatures will rebound nicely into the mid to upper
70s area-wide. This warmth will be short-lived, however, as a
cold front is forecast to drive across the region Saturday
night into Sunday. Gulf moisture ahead of the front will be
shunted well to our south, and coupled with unfavorable diurnal
timing, the front is expected to push through most of central
Illinois with weak instability. However, depending on the
frontal speed, there may be a brief window Sunday afternoon
across southeastern Illinois where a better thermodynamic
environment (750-1000 J/kg of MLCAPE and moderate shear) could
support a few strong to severe storms before the system exits
into Indiana. Behind the front, expect a dry start to the week
with temperatures returning to below-normal values by Monday.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1205 PM CDT Wed May 6 2026

A ridge of high pressure will move across central Illinois
tonight. A modest northwest breeze will continue the rest of
today but will drop back below 10 kt around sunset this evening.
Winds become light and variable or briefly calm under the ridge
axis, then set up out of the SW Thursday, with some gusts to
around 20 kt. Scattered showers and isolated storms are possible
as far south as the I-74 corridor as a weak upper level
disturbance passes through northern Illinois.

&&

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

&&

$$

KEY MESSAGES...Deubelbeiss
DISCUSSION...Deubelbeiss
AVIATION...Deubelbeiss