413
FXUS63 KILX 151726
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1226 PM CDT Fri Aug 15 2025

.KEY MESSAGES...

- Hazardous heat and humidity return today through early next
  week. The most oppressive conditions are expected on Saturday
  and Sunday, when heat indices could be as hot as 110 degrees.

&&

.DISCUSSION...
Issued at 218 AM CDT Fri Aug 15 2025

IR satellite imagery reveals a somewhat zonal, or at least
unamplified, upper level pattern early Fri AM. Upper level ridging
was present across the southern Plains/southeast CONUS, with a
subtle shortwave near the MS/AL border and a deeper wave over the
Canadian Prairie. Into this afternoon, the upper ridge is expected
to start amplifying, becoming centered over MO. Additional
expansion and amplification of this upper ridge is forecast into
this weekend. Beneath the ridge, a warm front is expected to lift
north today, boosting temps. The NBM has a 60-80% chance of at
least 90F across most of the area. With low to mid 70s dewpoints,
peak heat indices today should be near 100F.

The main concern this forecast period is a return to dangerous
heat and humidity, with the most oppressive conditions
anticipated Sat-Sun. On those days, high temps are forecast to be
in the mid/upper 90s and daytime dewpoints in the mid 70s,
resulting in peak heat indices between 100-110 degF. Central IL
will also be situated in a relatively weak sfc pressure pattern,
keeping wind speeds light (less than 10 mph) and therefore
offering little in the way of relief. WPC Heat Risk features the
entire ILX CWA in at least Major (level 3 of 4) Heat Risk for Sat-
Sun, and has some pockets of Extreme (level 4 of 4) Heat Risk.
This kind of heat/humidity will affect anyone without adequate
cooling and hydration. Heat Advisories will likely be needed for
this time period.

Circling back to precip chances over the next 48 hours, forecast
soundings show a layer of weak lapse rates (or in some models,
subtle capping) present above cloud bases this afternoon. Between
this and the height rises aloft (large scale subsidence), think
it`s unlikely we see any precip today, but did want to note that a
few CAMs are producing isolated showers this afternoon/evening.
There is also potential for upstream convection across IA this
afternoon to produce an MCV, although if that were to occur this
feature would be unlikely to reach central IL until late this
evening at which point the diurnal timing is less favorable for
storms. All told, the probability at any one location is less than
10% and therefore not mentioned in the official forecast.

A few CAMs also bring overnight convection across IA into northern
portions of the ILX CWA Sat AM. The favored corridor certainly
seems to be north of our area (closer to the IL/WI border), and
the 15.00z CAMs trended further north compared to the 14.12z runs.
There is enough uncertainty in this evolution that I wanted to
maintain low PoPs (15%) along the I-74 corridor overnight into Sat
AM. These may be removed if morning model guidance continues to
focus the precip across areas to the north. If storms do reach our
area, deep layer shear is quite weak (less than 20 kts), but
MUCAPE values of 2500- 4000 J/kg would support robust updrafts
capable of briefly reaching severe limits. The SPC Outlooks for
Fri-Sat do not include any of the ILX counties in a severe risk,
but a marginal risk is present across far northern IL where the
probability of storms is higher.

Into next week, the upper ridge retrogrades west towards the
Rockies, and the sfc front/storm track gradually shift south
towards the ILX CWA. Some timing uncertainty remains, owing in
part to the evolution of TC Erin and its subsequent impacts on the
large scale pattern, but blended guidance has the highest PoPs on
Tues-Wed (20- 40%). Machine learning guidance indicates a 5-15%
risk of severe storm hazards with the mid-week FROPA, which is the
equivalent of an SPC marginal risk. While instability may be
strong, weak shear (mid- level winds less than 20 kts) is likely
to be the limiting factor preventing a greater risk level.
Following FROPA, temps are expected to trend closer to seasonable
values but still remain a few degrees above normal (normal highs
are in the mid 80s).

Erwin

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1226 PM CDT Fri Aug 15 2025

Sprawling surface high pressure centered to our east should
maintain mostly sunny skies and generally light southerly winds
throughout the forecast period. While conditions will most likely
stay VFR, there is a small (10-15%) chance of a shower or storm
impacting any terminal tonight as a decaying line of storms
approaches central IL. If any of this activity affects the area
overnight into Saturday morning, then an outflow boundary could
serve as a lifting mechanism for one or two storms during the
afternoon. However, in each case, chances are low enough to
preclude PROB30 groups at any airfield.

Bumgardner

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Saturday to 8 PM CDT Sunday for
ILZ027>031-036>038-040>057-061>063-066>068-071>073.

&&

$$