993
FXUS63 KILX 291757
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1257 PM CDT Sun Jun 29 2025

.KEY MESSAGES...

- Hot and humid through Monday, with heat indices in the mid 90s.
  Conditions cool slightly for Tuesday and Wednesday, with highs
  in the mid 80s and heat indices below 90 degrees.

- Isolated to scattered storms are forecast through Monday.
  Locally heavy rainfall is possible, and there is a marginal risk
  (level 1 of 5) of severe storms, mainly on Monday. The primary
  hazard with any severe storms will be strong winds.

&&

.UPDATE...
Issued at 1055 AM CDT Sun Jun 29 2025

Forecast overall looked good today and just some minor adjustments
to pops and sky cover. Another very warm and humid day unfolding
with highs in the upper 80s to around 90F and heat indices peaking
in the mid to upper 90s and a few cities reaching around 100F.
Temps at 11 am were in the low to mid 80s with heat indices in the
upper 80s and lower 90s. Peoria had heat index up to 95F.

Radar mosaic shows isolated convection lingering over southeast IL
especially in Crawford county with locally heavy rains of three
quarter to 1.5 inches occuring this morning in southeast Clark and
northeast Crawford counties. Hutsonville coop near the Wabash
river in far northeast Crawford county had 0.89 inches of rain
early this morning. PW values of 1.70-1.85 inches southeast of
I-70 in tropical air mass, supporting pockets of very heavy
rainfall.

MCV over central/nw MO had more widespread convection over central
and northern MO and south central Iowa and tracking ESE toward
the MO/IL border at late morning. Most of this convection passes
sw of CWA this afternoon/evening but we have an unstable tropical
airmass in place so we continued 20-40% chance of convection, with
highest pops over southeast IL and sw CWA where pops were
increased. SB CAPEs currently run 2500-3500 j/kg over northeast
and eastern CWA so expect isolated to scattered convection to
develop here during the afternoon. SPC day1 outlook updated to
remove marginal risk of severe storms with damaging winds over
the IL river valley. Latest CAMs have backed off on convection
chances overnight over the IL river valley. Locally heavy rain
over 1 inch may be biggest threat over southern counties this
afternoon and early evening.

07

&&

.DISCUSSION...
Issued at 241 AM CDT Sun Jun 29 2025

*** THROUGH MONDAY ***

Early Sun AM, convection was ongoing near a cold front draped
across parts of WI/MN. Elsewhere, convergence along the leading
edge of the LLJ has led to showers/storms over cntrl MO. A moist
airmass remains in place across the region, with sfc Td in the low
70s and PWAT values around 1.5" sampled by the 29.00z KILX
sounding (with models suggesting that values approach 2" across
southern IL). With highs near 90 today, afternoon heat indicies
will once again climb to 95- 100 degF.

Over the next 24-36 hours, confidence is low in the convective
evolution as the environment remains weakly sheared and several
areas of convection are already ongoing. In this type of regime,
it`s difficult to put much stock in specific CAM runs. Overall,
CAM storm coverage is fairly low, so tried to keep PoPs at 30% or
lower through Sun night. Think the most likely time for scattered
precip today will be in the afternoon as a weak impulse aloft
shifts towards central IL in conjunction with peak diurnal
heating. Forecast soundings show mean cloud layer winds of less
than 10 kts, and given the high PWATs could see localized heavy
rain this afternoon. Similar to previous days in this pattern, an
isolated strong wind gust can`t be ruled out.

A more focused opportunity for storms is still expected on Monday
as the approaching cold front moves across the region, but even
for this front, CAM precip coverage appears scattered at best.
Felt the NBM PoPs (80-90%) were far too aggressive, and instead
went with 60- 70% (and wouldn`t be surprised if these are reduced
in later forecast updates). The main upper level trough will be
displaced to the north, resulting in unimpressive mid-level lapse
rates. There is modest mid-level flow, however, which results in
marginal deep layer shear of around 30 kts, perhaps sufficient to
offer some convective organization. Moderate instability is
expected to develop ahead of the front, particularly into Mon
afternoon (2000-3000 J/kg of SBCAPE). PWATs also remain very high,
around 2" which is above the 90th percentile for this time of
year. The main hazards will be damaging winds (particularly if a
more organized convective line forms) and locally heavy rainfall.
The front and any associated storms should shift completely SE of
the ILX CWA by late Mon eve.

*** TUESDAY - SATURDAY ***

No significant changes to the forecast for the middle of the week,
with a brief cooldown to seasonable temps on track as the post-
frontal airmass and sfc high pressure settle into the region. Tues
and Wed will feature highs in the mid 80s, lows in the mid 60s,
and afternoon heat indices in the mid/upper 80s. Confidence is
high that temps will trend warmer late week as an upper ridge
builds/shifts to the Midwest. Daily high temps push back to the
upper 80s/low 90s Thurs-Sun, with increasing humidity as well. The
upper ridge strength doesn`t appear as strong as our heat wave
last week, at least, but we`re still on track to see afternoon
heat indices in the upper 90s each day.

Precip chances have trended a bit lower for the 4th of July, now
at 15-20%, rather than 20-30%. This reduction is due to the fact
that the upper ridge axis is now progged to be directly over IL on
the 4th, which would promote synoptic-scale subsidence and help
limit storm chances/coverage. Guidance does have disturbances
tracking along the northern periphery of the ridge on the 4th,
resulting in better precip chances across the northern
Plains/upper Midwest, so we will still need to monitor this
pattern for shifts, as it would not take much to shift the precip
chances into our area. Even without an obvious lifting mechanism,
fcst soundings for the afternoon of the 4th show a well-mixed PBL
with uncapped profiles nearing the convective temp, which could
support isolated storms (hence the 15-20%). Precip chances
increase slightly into the holiday weekend (30% Sat, 40% Sun).

Erwin

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1245 PM CDT Sun Jun 29 2025

Unstable tropical air mass in place over central IL this afternoon
with SB CAPES 2-4k j/kg (highest ne CWA) and MLCApes 1-2k j/kg.
Isolated convection recently developed east of of I-57, east of
CMI and tracking slowly NE. An MCV over central and nw MO had more
widespread convection moving eastward toward the IL/MO border.
Carried VCTS over central IL airports this afternoon especially
from 19-24Z, but will need to possibly increase coverage at SPI
closest to MCV convection moving into west central IL early this
afternoon. MVFR conditions possible with gusty winds with
thunderstorms that occur. Very limited convection chances tonight
per CAMS and left it dry into Monday morning. A cold front moving
in during Monday afternoon to likely bring a band of convection
with it after the 18Z TAF period (after 18Z/1 pm Monday). South to
SSW winds 5-10 kts this afternoon to be around 5 kts tonight and
increase to 5-10 kts by midday Monday.



07

&&

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

$$