Iowa weather and outdoor projects
Iowa has a strongly continental climate: cold, windy winters and warm, humid summers. Spring and early summer are the wettest time of year, with frequent thunderstorms. Wind is common across the open landscape, which matters for spraying paint and weed killer.
Late August and September often give the best weather for staining and painting, with warm days, lower humidity and fewer storms. Hard freezes typically arrive in October. Many Iowans apply crabgrass preventer and lawn fertilizer in spring, when soil temperatures rise, and fall is a key season for lawn feeding.
Frost dates in Iowa
In Des Moines, the median last spring freeze (32°F) is around April 18 and the median first fall freeze is around October 20, a frost-free season of about 184 days.
In Dubuque, the median last spring freeze (32°F) is around April 28 and the median first fall freeze is around October 11, a frost-free season of about 165 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 Iowa
In Des Moines, the most reliable months are June–September. April–May and October can also work on the right days. November–March is too cold, with average highs around 40°F. In April and October, nights average about 42°F, so finish early on mild days and check the overnight low. May averages about 9 wet days a month, so wait for a clear stretch.
In Dubuque, the most reliable months are June–September. May and October can also work on the right days. November–March is too cold, with average highs around 36°F. In April, nights average about 37°F, too cold for the coating to dry and cure overnight. May averages about 8 wet days a month, so wait for a clear stretch. October is cool, with highs around 60°F, so choose the warmest afternoons.
Check this week’s hour-by-hour verdict with the deck staining forecast.
Best time to paint outside in Iowa
In Des Moines, the most reliable months are June–September. April–May and October can also work on the right days. November–March is too cold, with average highs around 40°F. In April and October, nights average about 42°F, so finish early on mild days and check the overnight low. May averages about 9 wet days a month, so wait for a clear stretch.
In Dubuque, the most reliable months are June–September. April–May and October can also work on the right days. November–March is too cold, with average highs around 36°F. April is cool, with highs around 58°F, so choose the warmest afternoons. May averages about 8 wet days a month, so wait for a clear stretch. In October, nights average about 40°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 Iowa
In Des Moines, the most reliable months are May–September. April and October can also work on the right days. November–March averages about 24 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. April and October bring about 5 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
In Dubuque, the most reliable months are May–September. October can also work on the right days. November–April averages about 23 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. October brings about 7 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 Iowa
In Des Moines, the most reliable months are June–September. May and October can also work on the right days. November–March is too cold, with average highs around 40°F. In April, nights average about 41°F, too cold for the coating to dry and cure overnight. May averages about 9 wet days a month, so wait for a clear stretch. October is cool, with highs around 63°F, so choose the warmest afternoons.
In Dubuque, the most reliable months are June–August. May and September can also work on the right days. October–April is too cold, with average highs around 42°F. In May and September, nights average about 50°F, so finish early on mild days and check the overnight low.
Check this week’s hour-by-hour verdict with the driveway sealing forecast.
Best time to fertilize or treat a lawn in Iowa
In Des Moines, the most reliable months are April–October. November–March is too cold, with average highs around 40°F.
In Dubuque, 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 36°F. April and October are cool, with highs around 59°F, so choose the warmest afternoons.
Check this week’s hour-by-hour verdict with the lawn fertilizer forecast.
How the weather differs across Iowa
| Place | Hottest month avg high | Coldest month avg low | Rain per year | Last spring freeze | First fall freeze |
|---|---|---|---|---|---|
| Des Moines | 86°F | 14°F | 37 in | April 18 | October 20 |
| Dubuque | 82°F | 11°F | 38 in | April 28 | October 11 |
Monthly weather in Des Moines
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 31°F | 14°F | 3 | 1.1 in | 63% | 30 |
| February | 36°F | 18°F | 4 | 1.3 in | 58% | 25 |
| March | 49°F | 30°F | 5 | 2.2 in | 48% | 19 |
| April | 62°F | 41°F | 8 | 4.0 in | 44% | 6 |
| May | 72°F | 52°F | 9 | 5.2 in | 49% | 0 |
| June | 82°F | 62°F | 7 | 5.3 in | 52% | 0 |
| July | 86°F | 66°F | 6 | 3.8 in | 53% | 0 |
| August | 84°F | 64°F | 6 | 4.2 in | 54% | 0 |
| September | 77°F | 55°F | 5 | 3.2 in | 49% | 0 |
| October | 63°F | 43°F | 5 | 2.8 in | 47% | 4 |
| November | 48°F | 30°F | 4 | 1.9 in | 53% | 17 |
| December | 36°F | 20°F | 4 | 1.6 in | 62% | 27 |
*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 Dubuque
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 27°F | 11°F | 4 | 1.3 in | 71% | 30 |
| February | 31°F | 15°F | 4 | 1.6 in | 66% | 26 |
| March | 44°F | 26°F | 5 | 2.3 in | 55% | 23 |
| April | 58°F | 37°F | 7 | 4.1 in | 49% | 8 |
| May | 69°F | 49°F | 8 | 4.3 in | 52% | 1 |
| June | 79°F | 59°F | 8 | 5.2 in | 55% | 0 |
| July | 82°F | 62°F | 6 | 4.8 in | 58% | 0 |
| August | 80°F | 60°F | 6 | 4.0 in | 59% | 0 |
| September | 73°F | 52°F | 6 | 3.8 in | 54% | 0 |
| October | 60°F | 40°F | 5 | 2.9 in | 52% | 7 |
| November | 45°F | 28°F | 5 | 2.2 in | 60% | 20 |
| December | 32°F | 17°F | 4 | 1.8 in | 71% | 29 |
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 DES MOINES INTL AP, DUBUQUE RGNL 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 Iowa?
In Des Moines, June–September. In Dubuque, June–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 Iowa?
Des Moines: around April 18; Dubuque: around April 28. 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 Iowa?
Yes, but it needs cold-weather practices. Des Moines averages about 82 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 Iowa?
In Des Moines, June–September. In Dubuque, June–August. Most sealers need 50°F or warmer for 24 hours and a dry day after. See the driveway sealing forecast.