661
FXUS63 KILX 031044
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
544 AM CDT Thu Jul 3 2025

.KEY MESSAGES...

- A stray shower can`t be ruled out north of I-74 late this
  afternoon (10-15% chance), otherwise mostly dry conditions will
  prevail through Friday (July 4).

- Hot and humid conditions are expected Friday (July 4) and
  Saturday, with highs in the low 90s and heat indices of 95 to
  100 degrees.

- Storm chances return Saturday night into Sunday (20-40% chance)
  as a cold front moves through. Locally heavy rainfall and a few
  strong wind gusts are possible.

&&

.DISCUSSION...
Issued at 149 AM CDT Thu Jul 3 2025

*** TODAY THROUGH INDEPENDENCE DAY ***

Upper ridging is in place over the central Plains early Thurs AM,
with various upper lows positioned across North America, the most
relevant of which is situated over southern California. As of
06z/1am, a scattered mid-level cloud deck was evident on satellite
imagery along/south of I-72. Some patchy fog development is
hinted at by the models (with the last four hours of HRRR runs
trending more bullish on the fog potential), and dewpoints have
been running higher than earlier forecasts suggested.
Additionally, with crops becoming quite developed across the area,
we`ve consistently seen shallow fog develop over the crops the
last several mornings. Confidence in the placement/extent of fog
development this morning is low, but included a `patchy fog`
mention for much of the area through 8am this morning.

While a stray shower can`t be ruled out near/north of I-74 today,
between height rises aloft (synoptic scale subsidence), little to
no organized low-level convergence, and forecast soundings
showing subtle inhibition present above the cloud base, am
struggling to find justification for `slight chance` (of storms)
wording in the forecast. HREF supports this line of thinking, with
the probability of measurable rainfall less than 15% at any one
location this afternoon/tonight. Our gradual warming trend
continues today, with highs a few degrees warmer than yesterday,
around 90F, and peak heat indices in the mid 90s.

Forecast for Friday (July 4) remains on track, with the upper
ridge axis expected to shift directly over the area, helping to
prevent precip development. Highs will be in the low 90s, with
afternoon dewpoints ranging from the mid 60s in SE IL to near 70F
NW of the IL River. This temp/dewpoint combo will push heat
indices into the upper 90s. By the time fireworks begin, temps
should fall into the low/mid 80s, with light winds out of the
south-southeast (5-10 mph). All in all, this is a welcome forecast
for those with outdoor plans on the 4th, just so long as caution
is exercised to stay cool/hydrated during the peak heating hours.

*** SATURDAY INTO NEXT WEEK ***

The aforementioned upper low over southern California will eject
onto the Plains this week, eventually bringing a cold front and
associated precip chances towards IL late Sat into Sun. Most of
the area will be dry through the day Sat, but some precip could
reach areas west of the IL River by Sat eve.

The parameter space continues to appear more conducive for
locally heavy rainfall than it does organized severe storms. Model
guidance has PWAT values around 2", above the 90th percentile for
early July. Fcst soundings show a deep warm cloud layer (>11
kft), which will support efficient rainfall rates. While the mean
cloud layer winds are not what I would consider weak (20 kt winds
out of the southwest), the orientation of these winds is roughly
parallel to the expected front. Based on forecast wind fields, the
MBE velocity (meso-beta scale elements) is just 4 knots,
suggesting that any backbuilding convection would train. Perhaps
the front is progressive enough to limit the heavy rain threat,
but global models do seem to slow the front as it shifts further
and further SE. The good news is that climatologically it is a
time of year where, thanks to the growing crops, we can handle
quite a bit of rainfall before flooding issues arise. Current FFG
suggests that rainfall amounts in excess of 1.5" per hour or 3-4"
in 6 hours would be necessary for flooding, and these values could
rise further with multiple warm/dry days expected between now and
Sunday.

In terms of severe storms, weak shear (less than 20 knots)
continues to look like a limiting factor. Instability will be
moderate (around 2000 J/kg), and with the high PWATs some
localized strong gusts/downbursts could occur.

Guidance seems to push the front completely south of the ILX CWA
by Mon eve (exact timing may still vary), but the pattern remains
unsettled as disturbances round a new upper ridge that develops
over the SW US. For next week, temps generally appear seasonable,
with the NBM 25th-75th percentile high temps ranging from mid 80s
to near 90F.

Erwin

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 543 AM CDT Thu Jul 3 2025

VFR conditions are favored through the period, although can`t
completely rule out some patchy MIFG resulting in MVFR visbys
during the first hour or two of the period. Winds will be light,
generally 5 knots or less, shifting from westerly this morning to
southerly overnight into Friday. There is a 10% chance of isolated
-TSRA at the I-74 terminals, but the odds are too low to warrant
mention in the TAF.

Erwin

&&

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

$$