Tornado Warning 50, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
631 PM CDT Fri Jul 3 2026

.KEY MESSAGES...

- An additional round of storms is expected this evening
  starting at 6 or 7 PM, and lasting through the overnight
  hours. Confidence on where the next round occurs remains low,
  but may favor the I-80 or perhaps even I-88 corridor.

- Additional rounds of storms may move through the area tomorrow
  and Sunday.

&&

.DISCUSSION...
Issued at 243 PM CDT Fri Jul 3 2026

Rest of Today/Tonight:

Round one of thunderstorms is surely living up to expectations
with numerous measured severe wind gusts ranging from 60 to 73
mph. While the main push of storms is now moving toward Lower
Michigan, a few more cellular storms continue to percolate along
the remnant outflow boundary stretching southwestward from
Joliet to Lacon to Macomb, Illinois. North of the outflow
boundary, it feels the most comfortable it has in the past week
with temperatures largely in the low to mid 70s. Meanwhile,
south of the front, it's hot and sticky with heat index values
in the 100 to 105F range.

Focus is on the potential for a second round of storms this
evening. While southwesterly flow on the southern side of the
outflow boundary is not particularly strong (10 to locally 15
kt), have been noting the beginning of the northward retreat of
the unstable airmass back toward northwestern Illinois. Just how
far northwest the unstable airmass retreats is an item of low
confidence, but suspect it will be able to reach I-80 and
perhaps even I-88 by this evening ahead of an upper-level
shortwave currently moving through the southern Iowa region. As
a result, concern remains for another round of storms near the
frontal boundary (perhaps extending eastward from ongoing storms
near Kansas City, MO) as the wave moves approaches our area.
Timing the second round still looks to start sometime in the 6
to 7 PM timeframe with scattered storms continuing through the
overnight hours.

While the wave of storms that came through earlier today were
anchored by a notable 500mb wind max, flow this evening will be
weaker and more on the order of 25-30 kt. As a result, current
thinking is that coverage of severe weather this evening will
not be as high as it was with the first round of storms.
Nevertheless, moisture-laden MUCAPE >3000 J/kg will still
support water-loaded microbursts with a threat for torrential
downpours and localized wind damage. In addition, with storms
more likely to adopt a west-to-east orientation this evening, do
have concern for localized flash flooding particularly if the
front does make it back toward the I-88 corridor where 3 to
locally 5 inches of rain fell last night. If it becomes clear
such a threat will materialize, will consider hoisting a short-
fused Flash Flood Watch.

Tomorrow / Independence Day:

At least isolated showers and storms may be ongoing at daybreak,
though most guidance suggests coverage should wane by mid-
morning. Global guidance than advertises another upper-level
shortwave or two pinwheeling into the area during the afternoon
hours, which will support additional rounds of thunderstorms. At
this point, confidence in where the frontal boundary (which
will mark the unstable airmass) will be by tomorrow afternoon
is quite low and depends on coverage of storms tonight. So,
unfortunately, cannot offer more than mid- range chance PoPs
areawide tomorrow in favor of further refinement as things
hopefully become more clear tonight. The same goes for Sunday.

Borchardt

Beyond the weekend the upper ridge begins to build back north
slightly with the embedded waves moving to our north. Meanwhile
another wave (or waves) will move within the ridge to our south
(and potentially stall out). Overall this favors shower/storm
coverage focusing mainly north or south of the area into mid-
week. Shower and storm chances return later in the week as the
ridge begins to break down again.

Petr

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 631 PM CDT Fri Jul 3 2026

The primary forecast concern remains thunderstorm timing,
focused on this evening and again Saturday afternoon.

Scattered thunderstorms continue to develop across eastern IA
and far northwest IL early this evening and this activity is
expected to move east southeast across northern IL and the
terminals during the mid/late evening hours. While there still
remains some uncertainty for coverage, medium confidence that at
least scattered thunderstorms will be moving through the
terminals over a 2-4 hour period and have included both vicinity
and tempo thunder mention. Appears most of this activity will be
south of the terminals by 06z. While isolated showers and
possibly a thunderstorm would be possible overnight into
Saturday morning, the next time period for thunderstorm mention
appears to be mid Saturday afternoon through early Saturday
evening. While there remains enough uncertainty for only prob
mention at this time, model trends suggest that another nearly
solid line of thunderstorms will be moving across northeast IL
and the Chicago terminals during this time period. Very heavy
rain, ifr vis/cigs and erratic/gusty winds will be possible with
all of the thunderstorms.

Outside of the thunderstorms, wind speeds are expected to be
under 10kts, light southerly or light and variable tonight,
light southwest Saturday morning and then likely shifting
easterly Saturday afternoon, with a lake breeze possible for
the Chicago terminals.

Some prevailing mvfr cigs are possible Saturday morning, but
confidence is low. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until 7 PM CDT this evening for ILZ023-ILZ032-
     ILZ033-ILZ039.

IN...Heat Advisory until 7 PM CDT /8 PM EDT/ this evening for
     INZ010-INZ011-INZ019.

LM...None.

&&

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