Illinois weather and outdoor projects
Illinois has a continental climate with cold winters, hot and humid summers and plenty of spring storms. Chicago is moderated by Lake Michigan: springs near the lake are cooler and fall stays milder a bit longer. Central and southern Illinois warm up earlier in spring.
Late May through June and September are the most reliable months for staining and painting. Summer can bring humid stretches and thunderstorms, so watch the overnight forecast. Winters bring many freeze-thaw cycles, which damage concrete that was not cured and sealed well, so the timing of fall pours matters.
Frost dates in Illinois
In Chicago (O’Hare), the median last spring freeze (32°F) is around April 16 and the median first fall freeze is around October 28, a frost-free season of about 193 days.
In Springfield, the median last spring freeze (32°F) is around April 14 and the median first fall freeze is around October 20, a frost-free season of about 187 days.
Frost dates matter for concrete, which must not freeze in its first 48 hours, for paint and caulk that need nights above their minimum, and for lawn care, since crabgrass preventer goes down as the soil warms in spring. See how late in fall you can stain, paint or seal.
Best time to stain a deck in Illinois
In Chicago (O’Hare), the most reliable months are May–September. April and October can also work on the right days. November–March is too cold, with average highs around 40°F. April is cool, with highs around 59°F, so choose the warmest afternoons. In October, nights average about 45°F, so finish early on mild days and check the overnight low.
In Springfield, the most reliable months are May–September. April and October can also work on the right days. November–March is too cold, with average highs around 45°F. In April and October, nights average about 44°F, so finish early on mild days and check the overnight low.
Check this week’s hour-by-hour verdict with the deck staining forecast.
Best time to paint outside in Illinois
In Chicago (O’Hare), the most reliable months are May–October. April can also work on the right days. November–March is too cold, with average highs around 40°F. In April, nights average about 40°F, so finish early on mild days and check the overnight low.
In Springfield, the most reliable months are May–September. March–April and October–November can also work on the right days. December–February is too cold, with average highs around 39°F. March and November are cool, with highs around 53°F, so choose the warmest afternoons. In April and October, nights average about 44°F, so finish early on mild days and check the overnight low.
Check this week’s hour-by-hour verdict with the exterior painting forecast.
Best time to pour concrete in Illinois
In Chicago (O’Hare), the most reliable months are May–September. April and October can also work on the right days. November–March averages about 22 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. April and October bring about 4 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
In Springfield, the most reliable months are May–September. April and October can also work on the right days. November–March averages about 21 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. April and October bring about 4 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
Check this week’s hour-by-hour verdict with the concrete pouring forecast.
Best time to seal a driveway in Illinois
In Chicago (O’Hare), the most reliable months are June–September. May and October can also work on the right days. November–April is too cold, with average highs around 43°F. In May, nights average about 51°F, so finish early on mild days and check the overnight low. October is cool, with highs around 63°F, so choose the warmest afternoons.
In Springfield, the most reliable months are May–September. April and October can also work on the right days. November–March is too cold, with average highs around 45°F. April and October are cool, with highs around 67°F, so choose the warmest afternoons.
Check this week’s hour-by-hour verdict with the driveway sealing forecast.
Best time to fertilize or treat a lawn in Illinois
In Chicago (O’Hare), the most reliable months are May–October. April can also work on the right days. November–March is too cold, with average highs around 40°F. April is cool, with highs around 59°F, so choose the warmest afternoons.
In Springfield, the most reliable months are April–June and August–October. March, July and November can also work on the right days. December–February is too cold, with average highs around 39°F. March and November are cool, with highs around 53°F, so choose the warmest afternoons. July is hot, with highs near 87°F, so start early and keep out of full afternoon sun.
Check this week’s hour-by-hour verdict with the lawn fertilizer forecast.
How the weather differs across Illinois
| Place | Hottest month avg high | Coldest month avg low | Rain per year | Last spring freeze | First fall freeze |
|---|---|---|---|---|---|
| Chicago (O’Hare) | 85°F | 19°F | 38 in | April 16 | October 28 |
| Springfield | 87°F | 20°F | 38 in | April 14 | October 20 |
Of the places above, Chicago (O’Hare) has the most good months for staining, painting and concrete combined (16 job-months), and Springfield has the fewest (15). If you live between them, expect something in between, and higher ground to be cooler with a shorter season.
Monthly weather in Chicago (O’Hare)
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 32°F | 19°F | 5 | 2.0 in | 67% | 28 |
| February | 36°F | 22°F | 5 | 2.0 in | 60% | 24 |
| March | 47°F | 31°F | 6 | 2.5 in | 53% | 20 |
| April | 59°F | 40°F | 7 | 3.8 in | 47% | 6 |
| May | 71°F | 51°F | 8 | 4.5 in | 49% | 0 |
| June | 80°F | 61°F | 7 | 4.1 in | 50% | 0 |
| July | 85°F | 66°F | 6 | 3.7 in | 50% | 0 |
| August | 83°F | 65°F | 7 | 4.3 in | 52% | 0 |
| September | 76°F | 57°F | 6 | 3.2 in | 51% | 0 |
| October | 63°F | 45°F | 6 | 3.4 in | 52% | 3 |
| November | 48°F | 34°F | 5 | 2.4 in | 58% | 15 |
| December | 37°F | 24°F | 5 | 2.1 in | 66% | 25 |
*Days with at least 0.1 inch of rain or melted snow. Freezing nights: average nights a month at or below 32°F. Humidity is calculated from NOAA hourly normal temperature and dew point at 3 PM.
Monthly weather in Springfield
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 36°F | 20°F | 5 | 2.0 in | 65% | 27 |
| February | 41°F | 24°F | 5 | 1.9 in | 59% | 23 |
| March | 53°F | 33°F | 6 | 2.8 in | 50% | 16 |
| April | 66°F | 43°F | 7 | 4.0 in | 46% | 4 |
| May | 76°F | 54°F | 8 | 4.5 in | 49% | 0 |
| June | 84°F | 63°F | 7 | 4.6 in | 52% | 0 |
| July | 87°F | 66°F | 5 | 3.9 in | 56% | 0 |
| August | 85°F | 64°F | 5 | 3.4 in | 55% | 0 |
| September | 80°F | 56°F | 5 | 2.9 in | 46% | 0 |
| October | 67°F | 45°F | 6 | 3.3 in | 46% | 4 |
| November | 53°F | 34°F | 6 | 2.7 in | 54% | 14 |
| December | 41°F | 25°F | 5 | 2.1 in | 65% | 24 |
Use the averages, then check the forecast
These ratings describe a typical month, not a particular week. A warm spell in a “poor” month can give you a good day, and a wet week can spoil a “good” one. Use this page to plan the season, then check the 7-day forecast for your ZIP code before you buy materials or book help. Each project forecast checks the hours after you finish too: overnight lows, dew and rain that would ruin fresh stain, paint, sealer or concrete.
About this data
Monthly temperatures, rain days, snowfall and freeze dates are NOAA National Centers for Environmental Information (NCEI) U.S. Climate Normals for 1991–2020 at CHICAGO OHARE INTL AP, SPRINGFIELD CAPITAL AP. Ratings apply the same temperature limits as our forecasts (for example, 50°F or warmer for deck stain and driveway sealer, and no freezing nights for new concrete) to the average month. Your product label always takes priority.
Frequently asked questions
When is the best time to stain a deck in Illinois?
In Chicago (O’Hare), May–September. In Springfield, May–September. Look for at least 24 dry hours before and after, and nights above about 40°F. The deck staining forecast checks your exact week.
When is the last frost in Illinois?
Chicago (O’Hare): around April 16; Springfield: around April 14. These are median dates from NOAA 1991–2020 normals, so a freeze after them happens in about half of years. Low spots and valleys freeze later in spring.
Can you pour concrete in winter in Illinois?
Yes, but it needs cold-weather practices. Chicago (O’Hare) averages about 78 freezing nights from December to February, so fresh concrete needs insulated blankets, a heated enclosure or an accelerated mix, and must not freeze in the first 48 hours. Many homeowners wait for spring.
What months are best for sealing a driveway in Illinois?
In Chicago (O’Hare), June–September. In Springfield, May–September. Most sealers need 50°F or warmer for 24 hours and a dry day after. See the driveway sealing forecast.