Union Center, Illinois Weather Forecast Discussion

554
FXUS63 KILX 131854
AFDILX
Area Forecast Discussion
National Weather Service Lincoln IL
154 PM CDT Sat Sep 13 2025
.KEY MESSAGES...
- There is a low chance (20%) for storms through this evening, and
  if storms do form they could pose a risk of strong winds and
  hail. There is a marginal risk (level 1 of 5) of severe storms,
  mainly east of I-55.
- Hot and mostly dry conditions are expected through mid-week,
  with highs in the low to mid 90s. Heat indices will be highest
  on Sunday, approaching 100 degrees west of I-55. Drought
  conditions are expected to persist or worsen.
- Temperatures will trend cooler during the latter half of the
  week, and some rain chances (20-40%) return to the forecast
  Thursday- Friday. While any rainfall will be welcome, rainfall
  amounts are unlikely to exceed 1" (less than 15% chance).
&&
.DISCUSSION...
Issued at 152 PM CDT Sat Sep 13 2025
*** THROUGH TONIGHT ***
A hot day continues across central IL, with temps in the upper
80s/low 90s as of 18z/1pm, with the exception of areas north of
I-74 where cloud cover and outflow from earlier convection has
kept temps in the low 80s. Areas of thunderstorms continue to
track roughly from De Kalb, IL, towards Crawfordsville, IN,
following along the eastern edge of the MUCAPE (instability)
gradient. The expectation is that this will remain the favored
corridor for t-storm activity this afternoon, but can`t rule out
some development along the remnant outflow positioned near the
I-74 corridor (winds to the south are out of the south-southwest,
while winds to the north are out of the southeast). This boundary
is fairly diffuse, with weak forcing, and forecast soundings
appear capped, even when looking at those from models like the NAM
which have a moist bias.
Between the weak boundary forcing, capping, and little to no
synoptic scale ascent (due to an upper ridge axis just west of the
area), am pretty skeptical that we see any additional storm
development in the CWA through this evening. This notion is
further supported by the CAMs, with the HREF PoPs below 10% for
much of the area through early evening, although the CAM
performance has been poor today, so this was given less weight
than the analysis presented above. If storms do form, there is a
conditional threat of severe wind or hail. The storms ongoing
across NWS LOT`s CWA (as of 18z/1pm) have produced hail up to
quarter size at times. A marginal risk (level 1 of 5) remains in
place for this conditional threat, mainly east of I-55.
The CAMs suggest additional development across IN tonight, some of
which could clip far eastern IL. Due to this potential, maintained
a low chance (20%) mention of precip in the forecast tonight,
primarily east of I-57. Some models hint at fog tonight,
especially north of our area, which makes sense given that is
where rainfall occurred today. For now, did not introduce patchy
fog into the official forecast but will have the next shift
reevaluate the potential.
*** SUNDAY INTO NEXT WEEK ***
A prolonged stretch of hot and mostly dry conditions are
anticipated this week as upper level ridging remains over the
Midwest. Well- above normal temps are expected through at least
Wed, with highs in the low to mid 90s. Dewpoints are forecast to
be higher with westward extent, and heat indices could push 100
degrees west of I- 55 tomorrow.
Upper level forcing will be weak beneath the upper ridge, but a
few isolated showers/storms can`t be ruled out each after as we
approach the convective temperature, particularly as you shift
further west into the higher moisture air. At any one location
though, precip chances will be less than 20% each day Sunday-
Wednesday. The lack of widespread, appreciable precipitation
combined with the well above normal temperatures means drought
will remain a top concern of the current forecast period. Several
counties or cities have implemented burn bans. For more specific
information on burn bans, please check with your local officials.
Guidance suggests that upper troughing currently over the NW CONUS
will slowly shift east, eventually breaking down the ridge over
the Midwest during the latter half of the work week. This should
usher in at least scattered precip chances (15-40% Thursday
through Saturday) and start a cooling trend in temperatures, at
least back towards seasonable values (low 80s), if not cooler.
Given the developing drought conditions, any rain will be a
welcome occurrence, especially after the upcoming hot/dry week.
However, I do want to note that this system is unlikely to
mitigate the drought, as there is less than a 15% chance for 1" of
rain through next Saturday.
Erwin
&&
.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1157 AM CDT Sat Sep 13 2025
VFR conditions are favored to continue through the period,
although there is some potential for nocturnal fog at the northern
terminals (20-30% chance of vis below 5 miles). For the afternoon,
thunderstorm activity seems most likely to stay north/east of the
terminals, but held onto a PROB30 for TSRA at KCMI during the
mid-afternoon as storms could pass fairly close by. At the other
terminals, chances of storms are not zero, but also not high
enough to warrant a mention in the TAF. Winds will be south-
southwesterly through this evening, the become variable tonight
through Sunday morning.
Erwin
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$

NWS ILX Office Area Forecast Discussion