National Weather Service Forecast for: Crystal Lake IL
Issued by: National Weather Service Chicago, IL
Updated: 2:41 am CDT Jun 30, 2026
 
Overnight

Overnight: Partly cloudy, with a low around 77. South southwest wind around 10 mph, with gusts as high as 20 mph.
Partly Cloudy

 Tuesday

Tuesday: Mostly sunny, with a high near 92. Heat index values as high as 104. Southwest wind 10 to 15 mph, with gusts as high as 30 mph.
Mostly Sunny

 Tuesday
Night
Tuesday Night: Mostly clear, with a low around 76. Southwest wind 10 to 15 mph, with gusts as high as 30 mph.
Mostly Clear

 Wednesday

Wednesday: Sunny, with a high near 94. Heat index values as high as 105. Southwest wind 10 to 15 mph, with gusts as high as 25 mph.
Sunny

 Wednesday
Night
Wednesday Night: Mostly clear, with a low around 77. South southwest wind 10 to 15 mph, with gusts as high as 25 mph.
Mostly Clear

 Thursday

Thursday: A 20 percent chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 92.
Sunny then
Slight Chance
T-storms
 Thursday
Night
Thursday Night: A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Partly cloudy, with a low around 73. Chance of precipitation is 60%.
Chance
T-storms then
Showers
Likely
 Friday

Friday: Showers likely, with thunderstorms also possible after 1pm. Partly sunny, with a high near 90.
Showers
Likely

 Friday
Night
Friday Night: Showers likely and possibly a thunderstorm before 1am. Partly cloudy, with a low around 70.
Showers
Likely
Lo 77 °F Hi 92 °F Lo 76 °F Hi 94 °F Lo 77 °F Hi 92 °F Lo 73 °F Hi 90 °F Lo 70 °F

Hazardous Weather Outlook
Extreme Heat Warning
 

Overnight
 
 Partly cloudy, with a low around 77. South southwest wind around 10 mph, with gusts as high as 20 mph.
Tuesday
 
 Mostly sunny, with a high near 92. Heat index values as high as 104. Southwest wind 10 to 15 mph, with gusts as high as 30 mph.
Tuesday Night
 
 Mostly clear, with a low around 76. Southwest wind 10 to 15 mph, with gusts as high as 30 mph.
Wednesday
 
 Sunny, with a high near 94. Heat index values as high as 105. Southwest wind 10 to 15 mph, with gusts as high as 25 mph.
Wednesday Night
 
 Mostly clear, with a low around 77. South southwest wind 10 to 15 mph, with gusts as high as 25 mph.
Thursday
 
 A 20 percent chance of showers and thunderstorms after 1pm. Mostly sunny, with a high near 92.
Thursday Night
 
 A chance of showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Partly cloudy, with a low around 73. Chance of precipitation is 60%.
Friday
 
 Showers likely, with thunderstorms also possible after 1pm. Partly sunny, with a high near 90.
Friday Night
 
 Showers likely and possibly a thunderstorm before 1am. Partly cloudy, with a low around 70.
Independence Day
 
 A chance of showers, with thunderstorms also possible after 1pm. Partly sunny, with a high near 87.
Saturday Night
 
 A chance of showers and thunderstorms. Mostly cloudy, with a low around 67.
Sunday
 
 A chance of showers and thunderstorms. Partly sunny, with a high near 86.
Sunday Night
 
 Partly cloudy, with a low around 65.
Monday
 
 Mostly sunny, with a high near 84.

 

Forecast from NOAA-NWS for Crystal Lake IL.