Colorado weather and outdoor projects
Colorado’s Front Range has a dry, sunny, high-elevation climate with big daily temperature swings. A 75°F afternoon in Denver can drop into the 40s at night, which matters for stain, paint and concrete that need to stay warm while they cure. The strong high-altitude sun also dries finishes quickly and fades them faster.
Spring is unpredictable, with late snow possible into May, and summer brings afternoon thunderstorms and hail on many days. Plan to work in the morning in summer. The Western Slope around Grand Junction is drier and warmer in summer. Freeze-thaw cycles through winter are hard on concrete, so curing and sealing new flatwork properly matters here.
Frost dates in Colorado
In Denver, the median last spring freeze (32°F) is around May 5 and the median first fall freeze is around October 9, a frost-free season of about 156 days.
In Grand Junction, the median last spring freeze (32°F) is around April 28 and the median first fall freeze is around October 16, a frost-free season of about 171 days.
How Colorado compares with other states
Denver is tied for the shortest deck staining season of the 50 state main stations (2 good months). Denver is tied for the 5th-shortest frost-free season of the 50 state main stations (156 days). Denver has the 6th-most freezing nights of the 50 state main stations (156 a year).
| Measure (Denver) | Value | Rank, highest first |
|---|---|---|
| Deck staining season | 2 good months | 46th of 50 |
| Frost-free season | 156 days | 45th of 50 |
| Freezing nights | 156 a year | 6th of 50 |
| Rainy days | 35 a year with 0.1 in or more | 45th of 50 |
| Days at 90°F or hotter | 46 a year | 19th of 50 |
| Summer afternoons | 24% humidity at 3 PM, June–August | 42nd of 47 |
Best time to stain a deck in Colorado
In Denver, the most reliable months are June and September. May and July–August can also work on the right days (average highs May 71°F, Jul 90°F, Aug 88°F). November–February is too cold, with average highs around 47°F. In March–April and October, nights average about 33°F, too cold for the coating to dry and cure overnight. In May, nights average about 44°F, so finish early on mild days and check the overnight low. July–August is hot, with highs near 89°F, so start early and keep out of full afternoon sun.
In Grand Junction, the most reliable months are September. April–June, August and October can also work on the right days. November–February is too cold, with average highs around 44°F. In March, nights average about 32°F, too cold for the coating to dry and cure overnight. July is hot, with average highs near 95°F and about 26 days a month at 90°F or more, so work early in the day. In April–May and October, nights average about 42°F, so finish early on mild days and check the overnight low. June and August are hot, with highs near 90°F, so start early and keep out of full afternoon sun.
Best time to paint outside in Colorado
In Denver, the most reliable months are June and September. April–May, July–August and October can also work on the right days. December–February is too cold, with average highs around 45°F. In March and November, nights average about 27°F, too cold for the coating to dry and cure overnight. In April–May and October, nights average about 38°F, so finish early on mild days and check the overnight low. July–August is hot, with highs near 89°F, so start early and keep out of full afternoon sun.
In Grand Junction, the most reliable months are May and September. April, June, August and October can also work on the right days. December–February is too cold, with average highs around 41°F. In March and November, nights average about 30°F, too cold for the coating to dry and cure overnight. July is hot, with average highs near 95°F and about 26 days a month at 90°F or more, so work early in the day. In April and October, nights average about 39°F, so finish early on mild days and check the overnight low. June and August are hot, with highs near 90°F, so start early and keep out of full afternoon sun.
Best time to pour concrete in Colorado
In Denver, the most reliable months are June–September. May can also work on the right days (average highs May 71°F). October–April averages about 22 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. May brings about 3 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
In Grand Junction, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 66°F, Oct 67°F). November–March averages about 25 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. April and October bring about 6 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
Best time to seal a driveway in Colorado
In Denver, the most reliable months are June–August. May and September can also work on the right days (average highs May 71°F, Sep 80°F). November–March is too cold, with average highs around 49°F. In April and October, nights average about 35°F, too cold for the coating to dry and cure overnight. In May and September, nights average about 47°F, so finish early on mild days and check the overnight low.
In Grand Junction, the most reliable months are June–September. May can also work on the right days (average highs May 77°F). November–March is too cold, with average highs around 47°F. In April and October, nights average about 39°F, too cold for the coating to dry and cure overnight. In May, nights average about 47°F, so finish early on mild days and check the overnight low.
Best time to fertilize or treat a lawn in Colorado
In Denver, the most reliable months are April–June and September–October. March, July–August and November can also work on the right days. December–February is too cold, with average highs around 45°F. March and November are cool, with highs around 54°F, so choose the warmest afternoons. July–August is hot, with highs near 89°F, so start early and keep out of full afternoon sun.
In Grand Junction, the most reliable months are April–May and September–October. March, June, August and November can also work on the right days. December–February is too cold, with average highs around 41°F. July is hot, with average highs near 95°F and about 26 days a month at 90°F or more, so work early in the day. March and November are cool, with highs around 55°F, so choose the warmest afternoons. June and August are hot, with highs near 90°F, so start early and keep out of full afternoon sun.
How the weather differs across Colorado
| Place | Hottest month avg high | Coldest month avg low | Rain per year | Last spring freeze | First fall freeze |
|---|---|---|---|---|---|
| Denver | 90°F | 18°F | 14 in | May 5 | October 9 |
| Grand Junction | 95°F | 17°F | 9 in | April 28 | October 16 |
Monthly weather in Denver
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 45°F | 19°F | 1 | 0.4 in | 36% | 29 |
| February | 46°F | 20°F | 2 | 0.4 in | 33% | 26 |
| March | 56°F | 28°F | 3 | 0.9 in | 26% | 23 |
| April | 62°F | 34°F | 4 | 1.7 in | 28% | 13 |
| May | 71°F | 44°F | 5 | 2.2 in | 31% | 3 |
| June | 83°F | 53°F | 4 | 1.9 in | 26% | 0 |
| July | 90°F | 60°F | 4 | 2.1 in | 23% | 0 |
| August | 88°F | 58°F | 4 | 1.6 in | 24% | 0 |
| September | 80°F | 50°F | 3 | 1.4 in | 23% | 1 |
| October | 65°F | 37°F | 3 | 1.0 in | 25% | 9 |
| November | 53°F | 26°F | 2 | 0.6 in | 30% | 23 |
| December | 44°F | 18°F | 1 | 0.3 in | 36% | 29 |
*Days with 0.1 inch of rain or more; column notes.
Monthly weather in Grand Junction
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 38°F | 17°F | 2 | 0.6 in | 54% | 30 |
| February | 46°F | 24°F | 2 | 0.5 in | 41% | 24 |
| March | 58°F | 32°F | 3 | 0.8 in | 27% | 17 |
| April | 66°F | 38°F | 3 | 1.0 in | 22% | 6 |
| May | 77°F | 47°F | 3 | 0.8 in | 19% | 1 |
| June | 89°F | 57°F | 2 | 0.4 in | 13% | 0 |
| July | 95°F | 64°F | 2 | 0.6 in | 17% | 0 |
| August | 91°F | 62°F | 3 | 0.9 in | 20% | 0 |
| September | 82°F | 53°F | 4 | 1.2 in | 22% | 0 |
| October | 67°F | 40°F | 3 | 1.0 in | 26% | 6 |
| November | 52°F | 28°F | 2 | 0.6 in | 36% | 23 |
| December | 39°F | 18°F | 2 | 0.6 in | 50% | 30 |
Source: NOAA NCEI U.S. Climate Normals 1991–2020 for DENVER INTL AP, GRAND JUNCTION WALKER FLD. 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 Colorado?
In Denver, June and September. In Grand Junction, September.
When is the last frost in Colorado?
Denver: around May 5; Grand Junction: around April 28.
Can you pour concrete in winter in Colorado?
Yes, with cold-weather practices: Denver averages about 84 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 Colorado?
In Denver, June–August. In Grand Junction, June–September.