Decatur, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

057
FXUS63 KILX 160546
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1246 AM CDT Sat May 16 2026

.KEY MESSAGES...

- Periodic storm chances will persist through early next
  week...with the greatest probability for convection focusing
  tomorrow...then again late Monday into Tuesday.

- Windy and very warm conditions are expected by Sunday and
  Monday as highs surge well into the 80s.

&&

.DISCUSSION...
Issued at 211 PM CDT Fri May 15 2026

*** A Few Thunderstorms Late Tonight into Saturday ***

Short-wave ridging in the wake of the morning MCS has led to
mostly sunny skies across much of central Illinois early this
afternoon...with 18z/1pm satellite imagery showing the only
lingering cloud cover near the Indiana border. Mostly clear and
dry conditions are expected to continue through this evening
before the low-level jet interacts with an approaching cold
front to trigger scattered showers and thunderstorms late
tonight into Saturday morning. The 12z May 15 NAM shows a
40-45kt 850mb jet developing from Texas northeastward to Iowa
after dark. Thunderstorms will initially develop along/ahead of
the cold front across portions of Wisconsin and Iowa this
evening, but these will tend to track northeastward and diminish
across the southern Great Lakes late tonight as they outrun the
jet. Meanwhile further S/SW, most CAMs indicate scattered
convection forming within the jet and just south of the cold
front across northern/central Missouri between 06z and 09z. This
is the activity we will initially have to keep an eye on as it
tracks eastward across mainly the southern half of the KILX CWA
toward dawn Saturday. With MUCAPEs of 1500-2000J/kg, the storms
will be able to maintain themselves as they push eastward:
however, weak 0-6km bulk shear of just 20-30kt will prevent
significant severe weather overnight. A few of the strongest
cells may be capable of producing gusty winds/small hail
along/southwest of a Macomb to Mattoon line late tonight through
mid-morning Saturday.

Once the initial round of showers dissipates and/or exits into
Indiana, the big question will be whether convection will be
able to re-develop Saturday afternoon. While deep-layer shear
will increase into the 30-40kt range, extensive cloud cover
early in the day will tend to suppress temperatures and instability.
The 12z HREF indicates mean SBCAPEs of just 500-1000J/kg by
peak heating. Several of the CAMs are skimpy on precip during
the afternoon...with both the HRRR and RRFS suggesting
development much further south across southern Illinois into the
Ohio River Valley where instability will be greatest. This
scenario of course depends upon what happens tonight. If the
storm clusters develop across Missouri and track eastward across
central Illinois Saturday morning as expected, then the severe
risk for the afternoon will remain low. The current Day 2 SPC
Convective Outlook features a Marginal Risk (level 1 of 5) for
severe weather on Saturday, and this seems reasonable based on
the latest thinking.

*** Stormy Weather Early Next Week ***

The cold front that will be approaching Illinois late tonight
will stall across the region on Saturday, then lift back
northward as a warm front Saturday night in response to
developing mid-level ridging. All models show central Illinois
firmly in the warm sector on Sunday, as S/SW winds gusting
25-30mph push afternoon highs into the middle to upper 80s.
Things get more interesting during the Monday/Tuesday time
period as a significant trough and its associated cold front
come into the picture. The 12z May 15 models are in much better
agreement concerning the timing of this process...with both the
GFS and ECMWF showing FROPA Tuesday afternoon/evening. Given
this trend, confidence is growing that significant rain/storm
chances will likely hold off until Monday night. While the
current forecast features likely PoPs Monday afternoon, think
these will eventually be lowered...as the primary focus for
widespread storms will initially be much further west across
eastern Kansas/western Missouri immediately ahead of the front.
This convection will eventually spill into the Illinois River
Valley by mid to late evening, posing a damaging wind/hail risk.
The storms will likely decrease in intensity overnight as they
push eastward across the I-55 corridor. The most recent SPC
outlook still highlights areas along/west of I-55 with a 15-30%
chance for severe.

With a slower FROPA expected, the likelihood of convective
re-development across parts of central Illinois on Tuesday
continues to grow. While it is still too early to pinpoint the
exact development zone, most models and conventional wisdom
suggests it will be along/east of I-55. SPC continues to show a
15-30% chance for severe across the entire KILX CWA, and this
seems reasonable until minor timing discrepancies and mesoscale
details are better resolved.

*** Blowing Dust Potential ***

With planting season in full swing and crops only just beginning
to emerge, there is plenty of bare soil to be blown about if the
proper conditions are met. Despite the expected rainfall late
tonight and Saturday, a warm and windy day on Sunday will help
dry the immediate topsoil. If showers/storms do not form within
the warm sector well ahead of the approaching cold front, there
is growing concern that S/SW winds gusting 30-40mph will lead
to additional drying and perhaps areas of blowing dust where
active plowing is occurring on Monday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1246 AM CDT Sat May 16 2026

Scattered tsra expected to develop after 10Z-12Z, continuing
through morning hours, and have included PROB30 for tsra with
MVFR vsby for this activity. While not included in TAFs, briefly
worse conditions possible in storms. Predictability of storms
later in the day is too low for mention in TAFs, but there
remains a low chance for storms the remainder of the 24 hour TAF
forecast period. Low level wind shear will continue through much
of the night from KSPI-KBMI eastward due to a SW 40 kt wind
aloft. Otherwise, surface winds S 10-12 kts overnight, with
gusts to around 20 kts developing by 18Z for most of the area.
Gusts decreasing after 00Z.

&&

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

&&

$$

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