FXUS63 KILX 180531
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1231 AM CDT Mon May 18 2026

.KEY MESSAGES...

- Several rounds of convection will impact central Illinois late
  tonight through Tuesday evening. While all severe weather
  hazards will be possible, damaging wind gusts in excess of
  60mph will be the most likely.

&&

.DISCUSSION...
Issued at 259 PM CDT Sun May 17 2026

*** Round One of Convection ***

19z/2pm regional analysis shows rapid thunderstorm development
across eastern South Dakota ahead of a short-wave trough
pivoting northeastward from Colorado. As this wave interacts
with a frontal boundary draped across the Plains, widespread
strong to severe convection will organize into one or more
linear structures as it gradually shifts eastward later this
evening into the overnight hours. CAMs exhibit a good deal of
spread concerning both the coverage and timing of the storms as
they cross the Mississippi River well after midnight. The NAM is
the fastest model, showing cells potentially arriving across the
far NW KILX as early as 09z/4am...while the HRRR continues to
lag by a couple of hours. Regardless of which solution pans out,
the storms will be entering an environment characterized by
ample elevated instability, but weak deep-layer shear. NAM
MUCAPEs range from 1500-2500J/kg ahead of the storms, while
0-6km bulk shear is just 25-30kt. Given the elevated nature of
the convection, think the primary severe weather risk will be
scattered damaging wind gusts from the Mississippi River
eastward to the I-55 corridor through late morning.  


*** Round Two of Convection ***

As the broken line of thunderstorms crosses I-55, it will begin
to encounter an increasingly unstable airmass across east- 
central and southeast Illinois where HREF mean SBCAPEs reach 
1500-2000J/kg. Once the storms become surface-based, all severe 
hazards will come into play east of I-55 Monday afternoon, 
including damaging wind gusts in excess of 60mph, hail larger 
than quarters, and isolated tornadoes. All model solutions show 
the storms exiting into the Ohio River Valley prior to sunset, 
followed by mainly quiet conditions across the board through the
evening.


*** Round Three of Convection ***

A similar process to what will happen tonight will unfold Monday
night as a vigorous short-wave noted on latest water vapor
imagery over Nevada rounds the base of the Rockies trough and
generates a renewed round of severe convection from Omaha and
Des Moines southwestward to Kansas City late Monday afternoon
and evening. These cells will also grow upscale into a line of
storms, then progress eastward into west-central Illinois
overnight. Damaging wind gusts and isolated tornadoes will be
the primary hazards between about 06z/1am and 11z/6am from the
Mississippi River eastward to the I-55 corridor.


*** Round Four of Convection ***

Outflow from the morning storms and/or the approaching synoptic
cold front will be the primary focusing mechanisms for
additional storms Tuesday afternoon and evening. While the exact
generation zone is still in question, am continuing to focus
attention on locations east of I-55 for the highest probability
of damaging wind gusts, large hail, and a couple tornadoes.
These storms will depart into Indiana by evening, followed by a
period of cooler and much quieter weather conditions Tuesday
night through Thursday before the next chance for showers
arrives by the end of the week.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1231 AM CDT Mon May 18 2026

Low level wind shear is expected through early morning across
central IL as strong SSW winds aloft around 50 kts continue. A 
line of thunderstorms will continue approaching from the west 
overnight, anticipated to arrive at KPIA by 12Z, KSPI and KBMI 
by 14Z, and KDEC/KCMI by 15Z. Have included a 3-hour tempo group
for MVFR cigs/vsbys for these thunderstorms, then scattered 
showers are likely to continue for a few to several hours after 
the storms, although with generally VFR conditions. Anticipate 
briefly worse conditions in any of the stronger storms. Winds S 
12-20 kts overnight with a few higher gusts. Winds increase to 
15-20 kts with gusts 25-30 kts after 12Z.

&&

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

&&

$$

KEY MESSAGES...Barnes
DISCUSSION...Barnes
AVIATION...37