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.
How Iowa compares with other states
Des Moines is tied for the 10th-most humid summer afternoons of the 47 state main stations (53% humidity at 3 PM, June–August). Des Moines has the 12th-most freezing nights of the 50 state main stations (128 a year). Des Moines has the 13th-shortest frost-free season of the 50 state main stations (184 days).
| Measure (Des Moines) | Value | Rank, highest first |
|---|---|---|
| Deck staining season | 4 good months | 20th of 50 |
| Frost-free season | 184 days | 38th of 50 |
| Freezing nights | 128 a year | 12th of 50 |
| Rainy days | 66 a year with 0.1 in or more | 32nd of 50 |
| Days at 90°F or hotter | 22 a year | 29th of 50 |
| Summer afternoons | 53% humidity at 3 PM, June–August | 10th of 47 |
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 (average highs Apr 62°F, May 72°F, Oct 63°F). 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 (average highs May 69°F, Oct 60°F). 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.
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 (average highs Apr 62°F, May 72°F, Oct 63°F). 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 (average highs Apr 58°F, May 69°F, Oct 60°F). 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.
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 (average highs Apr 62°F, Oct 63°F). 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 (average highs Oct 60°F). 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.
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 (average highs May 72°F, Oct 63°F). 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 (average highs May 69°F, Sep 73°F). 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.
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 (average highs Apr 58°F, Oct 60°F). 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.
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 0.1 inch of rain or more; column notes.
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 |
Source: NOAA NCEI U.S. Climate Normals 1991–2020 for DES MOINES INTL AP, DUBUQUE RGNL AP. See how the ratings work and how late in fall you can stain, paint or seal.
Frequently asked questions
When is the best time to stain a deck in Iowa?
In Des Moines, June–September. In Dubuque, June–September.
When is the last frost in Iowa?
Des Moines: around April 18; Dubuque: around April 28.
Can you pour concrete in winter in Iowa?
Yes, with 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.