Waterloo, IL Weather & Growing Conditions
Today
97°F
Mostly Sunny
Mostly sunny, with a high near 97. Heat index values as high as 100. West wind 3 to 7 mph.
7-day forecast
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Today | 97°F | Mostly Sunny | 3 to 7 mph W | 2% |
| Tonight | 72°F | Partly Cloudy | 2 to 6 mph S | 4% |
| Sunday | 93°F | Slight Chance Rain Showers then Slight Chance Showers And Thunderstorms | 5 mph W | 20% |
| Sunday Night | 67°F | Slight Chance Showers And Thunderstorms then Showers And Thunderstorms Likely | 7 mph N | 55% |
| Monday | 79°F | Showers And Thunderstorms Likely | 6 to 9 mph N | 65% |
| Monday Night | 59°F | Showers And Thunderstorms Likely then Slight Chance Showers And Thunderstorms | 6 to 9 mph N | 65% |
| Tuesday | 71°F | Slight Chance Rain Showers then Partly Sunny | 10 mph N | 24% |
| Tuesday Night | 54°F | Mostly Cloudy | 6 to 10 mph N | 6% |
| Wednesday | 73°F | Mostly Sunny | 8 mph N | 2% |
| Wednesday Night | 54°F | Partly Cloudy | 3 to 7 mph N | 0% |
| Thursday | 75°F | Mostly Sunny | 3 to 7 mph N | 1% |
| Thursday Night | 56°F | Partly Cloudy | 6 mph NE | 4% |
| Friday | 76°F | Partly Sunny | 3 to 7 mph NE | 6% |
| Friday Night | 56°F | Partly Cloudy | 6 mph NE | 6% |
Forecast source: National Weather Service (api.weather.gov). Updated through the day.
Growing snapshot for Waterloo, IL
Last spring frost
Apr 9
First fall frost
Oct 26
Growing season
197 days
Hardiness zone
7a
Explore more for Waterloo, IL: full frost dates · planting calendar · Illinois frost dates
Climate data from the nearest NOAA station, Festus, Mo (14.5 mi). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.