283
FXUS63 KILX 011044
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
544 AM CDT Mon Jun 1 2026

.KEY MESSAGES...

- There is a 30-40% chance of showers and storms this morning,
  mainly south of a Macomb to Lawrenceville line.

- Above normal temperatures are likely to persist into mid-June,
  with highs generally in the 80s. Humidity values are expected
  to increase late this week into early next week.

- Storm chances return to the forecast Friday into the weekend
  (30-50% chance).

&&

.DISCUSSION...
Issued at 222 AM CDT Mon Jun 1 2026

*** EARLY MORNING STORM CHANCES ***

A stationary boundary remains draped across south IA into SW
IL. Despite upper ridging in place, a subtle sfc low over E KS
has aided t-storm development across a moist warm sector, with
PWAT values near the low exceeding 1.5". Storm coverage has
expanded over the last hour (midnight to 1 AM, or 05-06z), with
the most relevant storms for our forecast purposes being those
extending from the KC metro eastward to north of Columbia, MO.
Cloud layer mean winds generally favor a NW-to-SE motion, which
would keep these storms south of the ILX CWA. However, mid-level
hodographs are straight, which favors storm splitting and we
have indeed seen several left- movers emerge. The Bunkers motion
for these left-movers is ENE, which does increase the precip
potential for the ILX CWA compared to the mean wind. In addition
to these storms, IR satellite continues to show scattered
altocumulus percolating along the stationary boundary (as of
06z/1am), and it would not be a surprise to see some showers or
storms pop along this corridor.

All told, we maintained a 30-40% chance of showers/storms
roughly along and south of a Macomb to Lawrenceville line
through early morning, with lesser chances (10-20%) to the
north. RAP-analysis shows moderate MUCAPE (approaching 2000
J/kg) and marginal shear (20- 30 kts) south of that
aforementioned Macomb-Lawrenceville line, so a few instances of
strong wind gusts or hail can`t be ruled out in those areas, but
overall the severe threat is low.

This disturbance is progged to drop south of the ILX CWA/US-50
corridor by 15-16z (10-11am), after which point precip should be
south of the US-50 corridor. For the rest of the day, an
isolated pop-up shower can`t be ruled out (10%), but most of the
area should stay dry.

*** DRY AIR MOVES IN ***

Both traditional and AI ensembles exhibit strong agreement in
the mid-week pattern, which will feature a persistent sfc high
pressure (around 1028-mb) over the Great Lakes and a building
ridge axis overhead. This will result in dry conditions, not
only in terms of no precip Tues-Thurs, but also in the form of
seasonably low dewpoints. As NE flow establishes this afternoon,
dewpoints begin lowering into the evening, with mid 40s
dewpoints expected Tues-Wed before starting to gradually trend
higher late in the week. With clear skies and plentiful
insolation on Tues-Wed, continued to lean warmer than the model
blend for forecast high temps, but given the dry airmass even if
the temps overperform and reach the mid to upper 80s heat
impacts are unlikely.

*** HUMIDITY BUILDS, STORM CHANCES RETURN ***

Weaker but broad sfc high pressure is set to shift SE of the
region by Thurs night, replacing our NE flow regime with SW flow
that will advect moisture northward. At the same time, the
upper ridge will be flattened and shift SE while the Midwest and
Plains transition to a zonal pattern with embedded waves set to
offer storm chances. Timing differences persist, which results
in the model blend delivering a prolonged window of chance PoPs
(30-50%). In reality, there is a strong signal for precip during
during the Fri-Sun window, it`s just a matter of when. The
probability of at least 0.10" of rain at some point this weekend
is 70-80% area-wide. Machine learning probs highlight Fri-Sat
as having a low chance (5-15%) of severe storms. At this range,
the limiting factor precluding higher severe probs is
questionable wind shear, with bulk shear values generally
forecast to be less than 25 kts.

Guidance steadily warms the temps through the weekend into
early next week, with highs in the mid 80s to low 90s at times.
Unlike our recent warm spell, this one is expected to feature
increasing moisture content, with dewpoints climbing from the
pleasant mid 40s Tues-Wed to the low 60s by Fri, and perhaps
reaching muggy low 70s values by Sun-next Mon. Those upper
60s/low 70s dewpoints could push peak heat indices into the mid
90s, which would be the highest heat indices for the region thus
far in 2026.

As is often the case when there is a hot/humid pattern in the
extended forecast, the challenge becomes whether precip or cloud
cover keeps the temps cooler than forecast at any point.
Unfortunately, these mesoscale details are impossible to resolve
at this range, it`s just something worth keeping in mind as
persistent heat and humidity is highlighted in subsequent
forecasts. For now though, the NBM interquartile range (IQR,
25th to 75th percentile) of high temps over the weekend is less
than 10 degF. For being 5-7 days into the forecast, that is a
relatively small IQR, and tells us that there is reasonable
agreement among the ensemble members. The Probabilistic Heat
Risk indicates that moderate heat impacts are possible this
weekend (30-60% chance), which would primarily impact those that
are sensitive to the heat or lack adequate cooling or
hydration. Above normal temps are likely to persist into the
second week of June (50-60%) as ensembles depict anomalous upper
ridging persisting over the Midwest.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 541 AM CDT Mon Jun 1 2026

Main concern is at the start of the period as a cluster of TSRA
shifting east across the southern half of IL. Included a tempo
group at KSPI through 13z, but expect the storms to stay south
of KDEC. The rest of the period should be VFR, with a cirrus
shield to start the period but shifting away with the storms and
giving way to scattered diurnal cumulus. Winds will generally be
ENE through the period, around 10 kts.

&&

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

&&

$$

KEY MESSAGES...Erwin
DISCUSSION...Erwin
AVIATION...Erwin