354
FXUS63 KLOT 200002
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
702 PM CDT Tue Aug 19 2025

.KEY MESSAGES...

- Dangerous swimming conditions expected at southern Lake
  Michigan beaches today through early Thursday.

- A chance for sprinkles or very light showers tonight into
  Wednesday morning.

- Patchy fog possible tonight into early Wednesday.

- Temperatures early to mid next week will likely be an early
  Fall preview!

&&

.DISCUSSION...
Issued at 246 PM CDT Tue Aug 19 2025

Conditions are quiet and rather comfortable out there this
afternoon. The cold front that moved across late last night
driving heavy showers and thunderstorms has since pushed away
from our CWA into central IL. Advecting in behind this front and
overspreading the area is a thick stratocumulus deck. The cold
advection and cloudy skies have kept temperatures largely in the
70s so far with only a couple of sites in our south reporting
80 as of 2 PM.

Waves are building on southern Lake Michigan this afternoon as
gusty northerly winds move over the water. The Michigan City
buoy is already reporting wave heights greater than three feet
and they`re climbing quickly, with a beach hazards statement in
effect for our Indiana counties. The high swim risk will take
hold of Illinois beaches this evening. Then expect dangerous
swimming conditions to persist through tomorrow and stretch into
at least Thursday morning.

A very subtle low level wave/baroclinic zone will be pushing
south across the region this evening into tomorrow. A number of
model camps are resolving southward-moving pockets of very light
rain or sprinkles overnight while the wave moves across, mostly
over areas near the lake. Boundary layer moisture will stretch
farther inland during the morning spreading light precip chances
west of the Chicago metro for the morning hours. As inversion
heights lift, the shallow unstable layer may become supportive
of true light showers for a period during the morning before
drier air advects in for the afternoon.

Additionally, there is a good-looking signal for areas of fog
to develop overnight with patches of dense fog even possible.
This is primarily a concern across the outlying suburbs and
outside of the Chicago metro. How much clearing skies see
tonight will also play a role in the fog potential, but that`s
rather uncertain.

A large upper high will park itself over the Four Corners
region for the back half of this week and spread a quiet upper
flow regime over the Midwest. This should bring dry and largely
sunny conditions to Thursday and Friday. Temperatures leading up
to this weekend should be seasonably warm in the upper 70s and
low 80s. A cold front looks to move across the region Friday
night and Saturday, but a lack of forcing and instability could
keep precip coverage rather low. High pressure should then build
in behind the front and keep conditions dry for Sunday.
Temperatures are expected to fall to the cooler side of average
early next week behind that cold front.

Doom

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 702 PM CDT Tue Aug 19 2025

Forecast concerns include...

Mvfr cigs overnight/Wednesday morning.
Chance of fog overnight/Wednesday morning.

Cigs have scattered out across northwest IL and lifted to vfr
for northeast IL with mvfr still across central IL and
northwest IN. Cigs are expected to lower back to low mvfr for
most of the area later overnight and then lift back through mvfr
Wednesday morning and then scatter out Wednesday afternoon.

Fog is expected south and west of the Chicago terminals
overnight into early Wednesday morning and there is the
potential for dense fog but confidence is low. Have added tempo
mention for RFD/DPA and trends will need to be monitored.

There is a chance of sprinkles/showers overnight into Wednesday
morning across northeast IL but confidence is too low for any
mention in this forecast.

Northeast winds at the Chicago terminals this evening will turn
back light northerly overnight then go back to northeast
Wednesday morning. Speeds into the 10-12kt range are expected
with gusts into the 15-20kt range possible in the afternoon. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through Thursday morning for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement through Thursday morning for INZ001-
     INZ002.

LM...Small Craft Advisory from 1 AM Wednesday to 4 AM CDT Thursday
     for the IL and IN nearshore waters.

&&

$$

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