2 products issued by NWS for: Markham IL
Hazardous Weather Outlook
Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
1143 AM CDT Sat Jul 18 2026
ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-191645-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
1143 AM CDT Sat Jul 18 2026 /1243 PM EDT Sat Jul 18 2026/
This Hazardous Weather Outlook is for portions of north central
Illinois...northeast Illinois and northwest Indiana.
.DAY ONE...This Afternoon and Tonight.
Weather hazards expected...
Elevated Thunderstorm Risk...with an associated:
Level 2 of 5 Damaging Wind Risk...up to 60 mph.
Level 1 of 5 Large Hail Risk...up to quarter size.
Limited Flooding Risk.
Limited Excessive Heat Risk.
High Swim Risk Lake Michigan Beaches tonight.
DISCUSSION...
Thunderstorms will continue to develop along a passing cold front
this afternoon, some of which could be strong to severe. The
biggest concerns with thunderstorms will be damaging wind gusts
and localized flooding. Small to marginally severe hail will be
possible as well. The highest thunderstorm coverage and greatest
severe threat are expected near and south of I-80.
High temperatures will reach the upper 80s and lower 90s today
with afternoon heat indices peaking around 100 degrees, especially
near and south of I-80.
Additionally, gusty northerly winds in the wake of the cold front
will bring hazardous swimming conditions to southern Lake
Michigan beaches tonight into Sunday morning.
.DAYS TWO THROUGH SEVEN...Sunday through Friday.
Sunday...
High Swim Risk Lake Michigan Beaches in the morning.
Monday...
Limited Flooding Risk.
Elevated Thunderstorm Risk...with an associated:
Level 2 of 5 Severe Thunderstorm Risk.
Tuesday...
Limited Thunderstorm Risk.
High Swim Risk Lake Michigan Beaches.
Wednesday...
High Swim Risk Lake Michigan Beaches.
DISCUSSION...
Additional rounds of thunderstorms are possible on Monday some of
which could be strong to severe.
.SPOTTER INFORMATION STATEMENT...
Spotters may be needed this afternoon.
GENERAL STORM MOTION OF THE DAY:
Moving toward the southeast at 30 mph.
$$
Air Quality Alert
ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-200500- Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage- La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford- Northern Cook-Central Cook-Southern Cook-Northern Will-Southern Will- Eastern Will- Including the cities of Rockford, Belvidere, Crystal Lake, Algonquin, McHenry, Woodstock, Waukegan, Buffalo Grove, Mundelein, Gurnee, Rochelle, Oregon, Byron, Dixon, DeKalb, Sycamore, Aurora, Elgin, Naperville, Wheaton, Downers Grove, Lombard, Carol Stream, Ottawa, Streator, La Salle, Mendota, Marseilles, Oswego, Yorkville, Plano, Morris, Coal City, Minooka, Kankakee, Bourbonnais, Bradley, Pontiac, Dwight, Fairbury, Watseka, Gilman, Paxton, Gibson City, Evanston, Des Plaines, Schaumburg, Palatine, Northbrook, Chicago, Cicero, Oak Lawn, Oak Park, La Grange, Calumet City, Oak Forest, Lemont, Orland Park, Park Forest, Joliet, Bolingbrook, Plainfield, Mokena, Channahon, Manhattan, Wilmington, Crete, Peotone, and Beecher 1231 PM CDT Sat Jul 18 2026 ...AIR QUALITY ALERT IN EFFECT NOW THROUGH SUNDAY NIGHT... The Illinois Environmental Protection Agency has issued an Areawide Air Pollution Action Day for Sunday July 19th for portions of Illinois. This is in addition to the ongoing Chicago Area Air Pollution Action Day in effect today. An Areawide Air Pollution Action Day is declared when weather conditions are such that widespread ozone and or particulate levels are forecast to be at OR ABOVE the Unhealthy for Sensitive Groups (USG) category in all or nearly all Illinois AQI forecast sectors. Areas both inside and outside of the Action Day coverage area may experience smoke/PM2.5 to a varying degree and duration both later today and Sunday. Those with air quality concerns or anyone in Illinois with outdoor plans is encouraged to check current NowCast readings or sign up for EnviroFlash alerts on AirNow. gov. Before going outside, checking the NowCast AQI will help identify periods of both poor and cleaner air quality regardless of the level of the daily forecasted AQI. AQI Category Guidance Unhealthy for Sensitive Groups (USG) - Members of sensitive groups may experience health effects. The general public is less likely to be affected. Sensitive groups: Make outdoor activities shorter and less intense. Its OK to be active outdoors, but take more breaks. Watch for symptoms such as coughing or shortness of breath. People with asthma: Follow your asthma action plan and keep quick relief medicine handy. People with heart disease: Symptoms such as palpitations, shortness of breath, or unusual fatigue may indicate a serious problem. If you have any of these, contact your health care provider. Unhealthy - Sensitive groups: Avoid long or intense outdoor activities. Consider rescheduling or moving activities indoors. Everyone else: Reduce long or intense activities. Take more breaks during outdoor activities. Media Contact...Illinois EPA $$