981
FXUS63 KLOT 071935
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
235 PM CDT Fri Aug 7 2026

.KEY MESSAGES...

- Low chance (20-30%) for scattered showers and
  thunderstorms tonight, mainly across northwest IL. If storms
  make it into the area, then locally gusty winds and heavy
  downpours would be possible.

- Active weather pattern to get underway Sunday with periods of
  thunderstorms through the at least the middle of next week.
  Some storms could be severe, especially Sunday and Monday.

&&

.DISCUSSION...
Issued at 235 PM CDT Fri Aug 7 2026

A subtle shortwave trough is progressing across the Upper
Midwest with a cold front lagging behind the wave and stretching
from central MN to eastern NE. Ahead of the front, a complex of
thunderstorms has developed in southern MN and northern IA
which has started to turn towards the south as of recent radar
trends. The expectation is for this thunderstorm complex to
continue to dive southward across eastern IA this evening and
gradually weaken as it does so. Therefore, dry conditions should
prevail locally with partly cloudy skies and temperatures in
the mid-80s this afternoon cooling into the upper 60s to around
70 overnight. However, with only modest capping being noted in
recent amdar soundings and the 18z DVN Raob; there is a low
chance that a few scattered showers or storms could drift into
northwest IL later this evening. If this was to occur, the main
concern with any showers/storms would be lightning and locally
heavy downpours but some locally gusty winds cannot be fully
ruled out. For now have opted to maintain a 20-30% chance for
showers and thunderstorms through our forecast area tonight as a
precaution.

By daybreak Saturday morning, any showers/storms that survive
into our area should be eroded leaving us with another tranquil
and seasonably warm summer day. Winds though will be out of the
northwest behind the aforementioned front, but temperatures are
still expected to top out in the mid-80s Saturday afternoon.
Otherwise, expect mostly sunny skies through Saturday evening.

Heading into Saturday night, a building ridge of over the
southwest CONUS will help to deepen a broad trough over the
Upper Midwest and northern Great Lakes. This will in turn
generate stout northwest flow over northern IL and northwest IN
and allow several shortwaves to dive through the region Saturday
night through at least the middle of next week. The first of
these shortwaves is forecast to move through the region Saturday
night into Sunday and lead to the development of a complex of
thunderstorms somewhere near the SD/MN border. Given that the
highest instability axis should be stretching from eastern IA
southeastward into central IL, this complex should traverse
somewhere near or west of this axis Saturday night and thus keep
the bulk of any storms west of us. However, if this axis is
able to shift east then the storm complex could brush our
western counties late Saturday night into Sunday morning. The
favored scenario right now is that the storms stay west of our
area Saturday night, but have opted to keep some 30-40% POPs in
the forecast for our western half to account for some lingering
uncertainty in the exact storm track.

Regardless on how Saturday night goes, a warm front is expected
to lift into northern IL and northwest IN on Sunday which will
surge a warm, humid, and unstable air mass into the area. Couple
this with the lingering ascent associated with the shortwave
aloft and conditions look to be favorable for additional
thunderstorms to develop Sunday afternoon and persist into the
evening. While guidance is in good agreement on thunderstorms
occurring Sunday, there continues to be some uncertainty in
storm coverage and the exact timeframe storms will occur. That
said, with the large amount of instability (3000-6000 J/kg) and
40-45 kts of deep layer shear any storms that develop on Sunday
could become severe and contain a threat for damaging winds,
hail, and maybe even a threat for tornadoes. With the
aforementioned uncertainties the latest Day 3 outlook from SPC
does have our area in a marginal (level 1 of 5) risk for this
potential.

An additional period of thunderstorms are forecast for Monday
as another shortwave pivots across the region. Similar to
Sunday, the environment will be warm, humid, and unstable which
will support a fair coverage of thunderstorms especially during
the afternoon and evening hours. However, confidence on coverage
and the exact timing of storms is low and will likely depend on
how storms evolve on Sunday. Nevertheless, any storms that
materialize on Monday will also have a chance to become severe
and thus SPC has put our area in the 15% (slight risk) outlook
for Monday.

Beyond Monday the forecast through the middle of next week
looks to favor more periods of showers and thunderstorms as
shortwaves continue to round the trough overhead. While there is
a chance that as repeated rounds of storms occur that the
outflows from storms push the better storm environment south of
the area and give us a break, confidence on when or if this will
occur remains low. So for now our official forecast will keep
40-60% chances for storms around through much of next week, but
suspect changes to these will occur as trends present
themselves. Otherwise, expect seasonably warm temperatures to
prevail with highs in the 80s and overnight lows in the 60s.

Yack

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1253 PM CDT Fri Aug 7 2026

Aviation forecast overview for 18Z:

- Diurnal Cu field expected to return this afternoon across the
  region.

- Frontal boundary expected to drop into the region overnight,
  monitoring trends for potential showers in KRFD area this
  evening ahead of the front and MVFR ceilings area-wide with
  the front.

- Southerly winds turn northwesterly through the period, with a
  potential lake breeze developing Saturday afternoon.

South-southwest winds this afternoon will continue to mix sfc
moisture into the low levels. This will expand the diurnal cu
field that is currently situated north and west of the metro
terminals. Expecting SCT-BKN, VFR ceilings for majority of this
afternoon ahead of an approaching frontal boundary. Storms
currently located across southeast Minnesota are forecasted to
drop south along the axis of greatest instability near the
Mississippi River Valley this evening. Decided to continue the
PROB30 group for RFD this evening, due to close proximity to the
axis. The frontal boundary is then expected to track through
the region early Saturday morning, bringing lowered
ceilings...however dry conditions are anticipated as the front
moves through.

Southerly winds, less than 10kts, will continue this afternoon
into the overnight before veering more westerly early Saturday
morning. After fropa Saturday morning, winds become northwesterly
by late morning, lasting through the afternoon. Model guidance
is suggesting a lake breeze develops midday Saturday, impacting
GYY and then MDW by mid-afternoon. Uncertainty exists with the
westward extent of the lake breeze, therefore left mention out
of ORD at this time.

Baker / Carlaw

&&

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

&&

$$

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