FXUS63 KLOT 221931
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
231 PM CDT Sat Aug 22 2026

.KEY MESSAGES...

- Isolated shower or storm possible (15-20% chance) this
  afternoon around Lake Michigan, and specifically northwest
  Indiana this evening and tonight.

- Dangerous swimming conditions at Porter County beaches today
  will include all Indiana and Cook County Lake Michigan beaches 
  late tonight and Sunday.

&&

.DISCUSSION...
Issued at 231 PM CDT Sat Aug 22 2026

It's a pleasant and quiet Saturday across the area with early 
afternoon temperatures in the upper 70s to around 80 and 
diurnally-driven cumulus starting to fill in overhead. Up 
north, a handful of showers and a couple of thunderstorms have 
recently blossomed along the eastern WI lakeshore with higher 
coverage found farther north near the Door Peninsula and UP of 
Michigan. These developed as a potent vort max and digging 
trough axis swing across the upper Midwest. The cold advection 
aloft has allowed for an ample reservoir of instability to build
around the region while plenty of broad forcing is around to 
drive scattered convection. Coverage will attempt to spread 
south over the next few hours and a few isolated showers/storms 
may attempt to go up over portions of far northeast IL and 
northwest IN before the end of the afternoon. A considerable 
amount of mid level dry air, however, should greatly limit 
overall coverage and make it largely difficult for cores to 
produce lightning. 

This evening, a secondary vort/backdoor cold front will drive 
down the windward side of the trough providing continued 
opportunities for showers and storms to develop over the lake 
during the night. The backed wind field should steer any 
evening/overnight activity into northwest Indiana. An isolated 
shower or two may even linger past daybreak into northern Porter
County. In the forecast, maintained slight chances for rain and
thunderstorms over and around the lake this afternoon which 
then focus into northwest Indiana for the evening and night. In 
addition to the precip potential, the added cooling aloft 
brought on by that secondary vort will further steepen up lapse 
rates over the mild lake waters such that waterspouts may 
develop over the lake this evening through early Sunday morning.

With the trough ejecting to our east tomorrow, surface high 
pressure will slide into the region and bring quiet conditions 
to the early part of next week. Afternoon temperatures are 
forecast in the middle to upper 70s on Sunday and Monday and 
around 80 for Tuesday. A synoptic system is favored to move 
across the upper Midwest during the middle of the week and bring
shower and storm chances to the area in the Tuesday night to 
Thursday window. A lot of uncertainty still revolves around this
system, including if there may be any appreciable severe 
threat, so we'll leave it at that for now and keep an eye on 
model trends over the coming days.

Doom

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1227 PM CDT Sat Aug 22 2026

A few isolated showers and perhaps an isolated thunderstorm are
possible this afternoon, primarily east of the Chicago
terminals. If confidence increases in coverage, then TAFs may
need to be amended to include a VCSH for a few hours this
afternoon. Otherwise, look for VFR conditions through the TAF 
cycle. 

Northwest winds will gust to around 20 mph this afternoon,
likely easing and losing gustiness as sunset approaches. Lake 
breeze will develop this afternoon and move through GYY 
resulting in a wind shift to lighter NE. Lake breeze is expected
to hug the shore over northeast IL remaining east of ORD and 
MDW through the afternoon. Toward sunset, as winds diminish, the
the lake breeze will probably make a run westward toward 
ORD/MDW. Best chance of a wind shift to easterly looks to be at 
MDW, but can't be ruled out at ORD.

If showers do develop near and over the lake this afternoon,
outflow from the showers could provide the lake breeze an
earlier westward push inland. Not out of the question this could
threaten a temporary easterly wind shift at MDW and possibly
even ORD later this afternoon.  

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement from late tonight through Sunday 
     evening for ILZ103-ILZ104.

IN...Beach Hazards Statement from late tonight through Sunday 
     evening for INZ001.

     Beach Hazards Statement through Sunday evening for INZ002.

LM...Small Craft Advisory from 4 AM to 7 PM CDT Sunday for Wilmette 
     Harbor to Calumet Harbor IL-Calumet Harbor to Gary IN.

     Small Craft Advisory until 10 PM CDT Sunday for Gary to Burns 
     Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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