278
FXUS63 KLOT 120645
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
145 AM CDT Wed Aug 12 2026

.KEY MESSAGES...

- Afternoon showers/storms expected to wane into this evening.

- Another round of showers/storms possible tonight (30-50%),
  including the potential for severe storms and heavy rainfall.

- Additional strong/severe storms possible Wednesday.

&&

.DISCUSSION...
Issued at 310 PM CDT Tue Aug 11 2026

Ongoing scattered showers and storms will linger this afternoon
and early evening in the wake of significant severe weather
earlier today. This activity is expected to wane over the next
several hours with convective inhibition/subsidence in place
across the CWA as the reinforced surface boundary has pushed south
of the area across central Illinois.

While this will likely lead to a lull in shower/storm chances this
evening, additional thunderstorm development will be possible
overnight tonight -- primarily across northeast Illinois/northwest
Indiana, including the Chicago area. The aforementioned boundary
is expected to work back north across the area with time this
evening with showers/storms possibly training along/north of said
boundary. Strong buoyancy aloft on the order of 3,500+ MUCAPE
combined with deep-layer shear ~35 kts will support a continued
threat for strong/severe storms tonight. Given anticipated
convective evolution/training of storms, perhaps of equal concern
will be the potential for heavy rainfall/flooding later tonight.
Storms in an environment characterized by ~2" PWATs would lead to
very efficient rainfall, and potentially bring an additional 1-2"+
of rain to areas that already saw heavy rainfall earlier in the
day. While uncertainty remains relatively high at this time
(20-30% PoPs tonight), another round of impactful storms remains
possible tonight.

The aforementioned boundary is expected to remain draped across
the area during the day Wednesday with ample instability in place
along and to its south, supporting continued thunderstorm chances
Wednesday morning into Wednesday evening. Damaging winds will be
the primary threat with strongest storms, especially if another
line organizes and tracks from northwest to southeast across the
warm sector south of the front during the day. Hail and locally
heavy rainfall will also be possible.

Precise details in regards to timing and impacts becomes more
obscure beyond Wednesday, but additional rounds of thunderstorms
will be possible into the end of the week as the boundary lingers
across the area and keeps a warm, moist airmass in place with
relatively strong northwest flow aloft. A more substantial break
in storm chances may not come until late this upcoming weekend or
early next week as surface high pressure may settle more firmly
over the Midwest.

Cornish

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 145 AM CDT Wed Aug 12 2026

Key Messages:

- There is a low (~20-25%) chance for storms to affect the
  terminals overnight through early this morning.

- There is an increasing likelihood of storms affecting the
  terminals between mid-morning and mid-afternoon today. Strong
  to severe wind gusts will be possible with these storms.

- Lowered ceilings and possibly lowered visibilities are
  expected overnight through early this morning. LIFR/IFR
  conditions will be possible, especially at RFD, DPA, and GYY.


Isentropic ascent atop a surface boundary may attempt to
initiate showers and storms near this boundary through the
night. Thus far, convection has struggled to develop in
northern Illinois. There may be a better chance for something to
develop later tonight, but confidence in that is fairly low. It
also appears that the surface boundary may remain far enough to
the south and southwest of the terminals for any convection
that develops near it to remain south of the terminals, so the
probability of showers/storms affecting the terminals later
tonight appears to be low enough (20-25%) to not carry any
formal SHRA or TSRA mentions in the TAFs at this time. However,
observational trends will need to be monitored closely, and it
can`t be ruled out that such a mention will need to be
reintroduced into the TAFs at some point.

It appears that the best opportunity for storms to affect the
terminals today will come between mid-morning and mid-afternoon
as a convectively-enhanced disturbance associated with an
organized thunderstorm complex in northern Nebraska approaches
the area. Similar to yesterday, an organized bow or line of
storms may develop and track through the area, producing swaths
of severe wind gusts in excess of 50 kts. There is still some
uncertainty in just how far north the northern terminus of this
thunderstorm complex will end up, but there has been enough
consistency in the most recent high-resolution model solutions
to warrant the introduction of TEMPO groups for TSRA at the
Chicago metro terminals and a PROB30 group for TSRA at RFD. That
said, if several storms end up lighting up along the
aforementioned surface boundary tonight, then that may increase
the chances that this midday thunderstorm complex will end up
passing south of the terminals later today.

Lastly, patchy MVFR ceilings are currently being observed in the
area at press time, and it is possible that lower ceilings
(possibly IFR or LIFR) could be observed later tonight through
the early-mid morning. Fog/mist may develop in some areas as
well and could also result in IFR or LIFR conditions being
observed, especially at RFD, DPA, and GYY. Another episode of
low ceilings and visibilities could occur early Thursday
morning, and that potential will need to be assessed in greater
detail for forthcoming TAF issuances.

Ogorek

&&

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

&&

$$

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