824
FXUS63 KLOT 100800
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
300 AM CDT Mon Aug 10 2026

.KEY MESSAGES...

- Additional periods of storms are expected at times through
  mid-week. Some of these storms could be severe and lead to
  additional flooding.

&&

.DISCUSSION...
Issued at 300 AM CDT Mon Aug 10 2026

Forecast remains complex through mid-week, as a nearly
stationary frontal boundary lingers across the forecast area
beneath an active west-northwest flow pattern aloft. Periodic
shower and thunderstorm chances will persist with somewhat low
confidence in timing and coverage, ultimately modulated by
individual short waves and daily diurnal heating and instability
trends. Episodes of severe weather and locally heavy rainfall
remain possible.

In the near-term, latest surface analysis depicts a nearly
stationary frontal boundary stretching from an area of low
pressure over western KS northeast into western IA, then east
along roughly the I-80 corridor across northern IL/northwest IN.
A very warm/humid airmass is in place along/south of the
boundary, characterized by temps in the upper 70/around 80 and
dew points in the mid-70s at this late night hour. Aloft,
seasonably fast west-northwest flow was in place across the
region, supplying a track for a series of mid-level short wave
disturbances of varying amplitude. One such wave is currently
tracking from IA into northern IL, supporting a southwesterly 35
kt low-level jet atop the low-level frontal zone into northeast
IL/northwest IN. Several clusters of strong thunderstorms had
developed in the enhanced warm/moist advection regime associated
with this jet last evening, with a small MCS remaining across
our southern tier of cwa counties as of 2 AM on the nose of the
jet in the vicinity of the surface frontal boundary. Given
ML/MUCAPE values in the 3000-3500 J/kg range, 35-40 kts of
effective shear and precipitable water values near 2 inches,
severe weather and locally heavy rainfall remain a concern with
these storms for the next hour or so, before they eventually
slide southeast of the area toward/just after daybreak as the
low-level jet gradually veers more westerly and weakens with the
passage of the mid-level wave.

Once these storms exit the area, there should be a bit of a
lull in convection in the wake of the departing short wave and
during our diurnal instability minimum. Can`t completely rule
out some isolated elevated shower or thunderstorm development
however, due to the presence of the front/baroclinic boundary
and weaker but still persistent warm/moist advection. Chances
should increase again at least a bit toward midday and into this
afternoon however, as another weak wave or MCV (currently
approaching the Omaha vicinity) tracks east during a more
favorable diurnal time. CAM guidance loosely depicts this,
though differences in coverage and timing details are evident.
Additional development also appears possible later this evening,
as the nocturnal low-level jet modestly increases atop the
frontal zone. There does appear to be a somewhat consistent
signal however, amongst both CAM and global guidance, for an MCS
to develop over NE/SD later tonight which would approach the
forecast area around/after daybreak Tuesday. This supports the
highest pops (60-70%) during Tuesday, and have limited other
mentions to just chance (20-40%) later today and tonight. Given
otherwise similar instability/shear and moisture parameters, we
remain in SPC/WPC slight risks for severe weather and excessive
rainfall during these periods.

No significant change in the pattern is evident into mid-week
(Wednesday, possibly Thursday), though confidence gradually
decreases based on impacts of any preceding convective/MCS
outflow impacts. Global ensembles continue to show a signal for
our frontal boundary to shift a little farther south Thursday
night and Friday, which may decrease our shower/thunderstorm
potential briefly late in the week, though this signal is weaker
than earlier runs and there are indications that the front may
lift back into the area next weekend. Thus, it appears that our
seasonably warm/humid and periodically stormy pattern may
persist for much of the forecast period.

Ratzer

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 131 AM CDT Mon Aug 10 2026

Key Messages:

- Scattered showers and possibly a few storms will continue
  near the terminals overnight.

- There is a potential for MVFR (or lower) ceilings and/or
  visibilities through this morning.

- Additional waves of showers and storms are possible at and
  near the terminals today, but a high degree of uncertainty
  remains regarding the timing and coverage of this activity.


The worst of tonight`s thunderstorm activity has pushed east and
south of the terminals, but scattered showers will continue to
fester near the terminals for at least a few more hours tonight.
A few additional storms may develop, but their coverage should
be more isolated and they should be less intense than the
earlier storms.

Patchy MVFR ceilings have developed in the wake of the earlier
thunderstorm activity, and the expectation is for the footprint
of these lower ceilings to expand later overnight and past
daybreak. Some sites could hold onto MVFR ceilings well into
this afternoon, but confidence in ceiling trends is low on the
whole. Additionally, fog may also develop overnight as a result
of the excess low-level moisture in the area. The greatest
signal for visibility reductions across the latest available
forecast guidance suggests that RFD is the most likely of our
TAF sites to be affected by this, but observational trends will
need to be monitored closely.

Additional showers and thunderstorms may develop in the area
later today, but the exact timing and coverage of this potential
activity remains highly uncertain. Opted to introduce two PROB30
groups into the TAFs to highlight the time windows when
convection is most likely to affect the terminals. The first
window is tied to a convectively-enhanced disturbance that may
emanate from the central Plains tonight and reach our area
towards midday/the early afternoon. It is not yet clear how
well-defined this disturbance will be, whether we`ll still be
capped for stronger surface-based thunderstorms to develop
as it arrives, and whether the axis that the potential
thunderstorm may focus along will remain south of the terminals,
so opted to carry -SHRA in this PROB30 group for now as just
seeing some scattered high-based showers is also very much a
possibility during this time window. The second window is tied
to another upper-level disturbance that is progged to arrive
sometime late this afternoon or evening. Thunderstorms,
including strong to severe thunderstorms with strong winds and
hail, appear to be more likely to occur during this time window
compared to earlier, but exactly where and when they will
develop remains uncertain. All in all, a lot of uncertainty
remains regarding the thunderstorm potential for later today,
and additional changes to the TAFs will likely be needed as
observational trends become clearer.

Lastly, confidence in wind direction trends for today is also
fairly low, largely as a result of the thunderstorm-related
uncertainties. Outside of any thunderstorm influence though,
surface flow should remain at or under 10 kts through the TAF
period with a generally easterly or northeasterly direction
favored at ORD, MDW, and GYY from around midday through tonight
as a result of a weak lake breeze/onshore flow.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.

IN...None.

LM...None.

&&

$$

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