Idaho weather and outdoor projects
Southern Idaho around Boise and Pocatello has a dry climate with hot summer days, cool nights and cold winters. Summer is reliably dry, which makes it a good season for staining and painting, but the big swing between day and night temperatures means the night after you finish can be cold even in late spring and early fall.
The Panhandle in the north is wetter and more like the Pacific Northwest, with more cloud, rain and snow. Late summer can bring wildfire smoke across much of the state. Spring and fall frost dates come early at higher elevations, so the concrete and paint season there is short.
Frost dates in Idaho
In Boise, the median last spring freeze (32°F) is around April 24 and the median first fall freeze is around October 21, a frost-free season of about 179 days.
In Pocatello, the median last spring freeze (32°F) is around May 23 and the median first fall freeze is around September 18, a frost-free season of about 117 days.
How Idaho compares with other states
Boise is tied for the shortest deck staining season of the 50 state main stations (2 good months). Boise is tied for the 4th-least humid summer afternoons of the 47 state main stations (20% humidity at 3 PM, June–August). Boise has the 7th-fewest rainy days of the 50 state main stations (38 a year with 0.1 in or more).
| Measure (Boise) | Value | Rank, highest first |
|---|---|---|
| Deck staining season | 2 good months | 46th of 50 |
| Frost-free season | 179 days | 39th of 50 |
| Freezing nights | 108 a year | 19th of 50 |
| Rainy days | 38 a year with 0.1 in or more | 44th of 50 |
| Days at 90°F or hotter | 55 a year | 14th of 50 |
| Summer afternoons | 20% humidity at 3 PM, June–August | 43rd of 47 |
Best time to stain a deck in Idaho
In Boise, the most reliable months are June and September. April–May, August and October can also work on the right days. November–February is too cold, with average highs around 43°F. In March, nights average about 35°F, too cold for the coating to dry and cure overnight. July is hot, with average highs near 93°F and about 22 days a month at 90°F or more, so work early in the day. In April–May and October, nights average about 43°F, so finish early on mild days and check the overnight low. August is hot, with highs near 91°F, so start early and keep out of full afternoon sun.
Pocatello has no month that is easy for this job on average; the best chances come in May–September. November–March is too cold, with average highs around 41°F. In April and October, nights average about 33°F, too cold for the coating to dry and cure overnight. In May–June and September, nights average about 43°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.
Best time to paint outside in Idaho
In Boise, the most reliable months are May–June and September. March–April, August and October can also work on the right days. November–February is too cold, with average highs around 43°F. July is hot, with average highs near 93°F and about 22 days a month at 90°F or more, so work early in the day. March is cool, with highs around 56°F, so choose the warmest afternoons. In April and October, nights average about 41°F, so finish early on mild days and check the overnight low. August is hot, with highs near 91°F, so start early and keep out of full afternoon sun.
In Pocatello, the most reliable months are June. May and July–September can also work on the right days. November–February is too cold, with average highs around 38°F. In March–April and October, nights average about 31°F, too cold for the coating to dry and cure overnight. In May and September, nights average about 41°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.
Best time to pour concrete in Idaho
In Boise, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 62°F, Oct 65°F). November–March averages about 20 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 Pocatello, the most reliable months are June–August. May and September can also work on the right days (average highs May 69°F, Sep 77°F). October–April averages about 23 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. May and September bring about 4 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
Best time to seal a driveway in Idaho
In Boise, the most reliable months are June–September. May can also work on the right days (average highs May 72°F). November–March is too cold, with average highs around 46°F. In April and October, nights average about 41°F, too cold for the coating to dry and cure overnight. In May, nights average about 48°F, so finish early on mild days and check the overnight low.
In Pocatello, the most reliable months are July. June and August–September can also work on the right days (average highs Jun 79°F, Aug 88°F, Sep 77°F). November–April is too cold, with average highs around 44°F. In May and October, nights average about 36°F, too cold for the coating to dry and cure overnight. In June and August–September, nights average about 46°F, so finish early on mild days and check the overnight low.
Best time to fertilize or treat a lawn in Idaho
In Boise, the most reliable months are April–June and September–October. March and August can also work on the right days (average highs Mar 56°F, Aug 91°F). November–February is too cold, with average highs around 43°F. July is hot, with average highs near 93°F and about 22 days a month at 90°F or more, so work early in the day. March is cool, with highs around 56°F, so choose the warmest afternoons. August is hot, with highs near 91°F, so start early and keep out of full afternoon sun.
In Pocatello, the most reliable months are May–June and September–October. March–April and July–August can also work on the right days. November–February is too cold, with average highs around 38°F. March–April is cool, with highs around 55°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.
How the weather differs across Idaho
| Place | Hottest month avg high | Coldest month avg low | Rain per year | Last spring freeze | First fall freeze |
|---|---|---|---|---|---|
| Boise | 93°F | 25°F | 12 in | April 24 | October 21 |
| Pocatello | 89°F | 17°F | 12 in | May 23 | September 18 |
Of the places above, Boise has the most good months for staining, painting and concrete combined (10 job-months), and Pocatello has the fewest (4).
Monthly weather in Boise
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 39°F | 26°F | 5 | 1.4 in | 64% | 26 |
| February | 46°F | 29°F | 4 | 1.0 in | 51% | 20 |
| March | 56°F | 35°F | 5 | 1.3 in | 38% | 11 |
| April | 62°F | 40°F | 4 | 1.2 in | 32% | 5 |
| May | 72°F | 48°F | 4 | 1.4 in | 29% | 1 |
| June | 81°F | 54°F | 2 | 0.8 in | 24% | 0 |
| July | 93°F | 62°F | 1 | 0.2 in | 18% | 0 |
| August | 91°F | 61°F | 0 | 0.2 in | 19% | 0 |
| September | 80°F | 53°F | 1 | 0.4 in | 23% | 0 |
| October | 65°F | 42°F | 2 | 0.8 in | 31% | 4 |
| November | 49°F | 32°F | 4 | 1.2 in | 49% | 16 |
| December | 39°F | 25°F | 5 | 1.5 in | 63% | 25 |
*Days with 0.1 inch of rain or more; column notes.
Monthly weather in Pocatello
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 34°F | 17°F | 4 | 1.1 in | 67% | 29 |
| February | 39°F | 20°F | 3 | 1.0 in | 59% | 25 |
| March | 51°F | 28°F | 4 | 1.2 in | 43% | 23 |
| April | 59°F | 33°F | 4 | 1.2 in | 33% | 14 |
| May | 69°F | 40°F | 4 | 1.4 in | 30% | 4 |
| June | 79°F | 46°F | 3 | 0.9 in | 27% | 0 |
| July | 89°F | 52°F | 2 | 0.5 in | 21% | 0 |
| August | 88°F | 51°F | 2 | 0.5 in | 19% | 0 |
| September | 77°F | 42°F | 3 | 0.9 in | 23% | 3 |
| October | 62°F | 33°F | 3 | 1.0 in | 32% | 15 |
| November | 46°F | 24°F | 3 | 0.9 in | 49% | 25 |
| December | 34°F | 17°F | 4 | 1.1 in | 67% | 29 |
Source: NOAA NCEI U.S. Climate Normals 1991–2020 for BOISE AIR TERMINAL, POCATELLO 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 Idaho?
In Boise, June and September. In Pocatello, no month is reliably good on average; pick dry spells carefully.
When is the last frost in Idaho?
Boise: around April 24; Pocatello: around May 23.
Can you pour concrete in winter in Idaho?
Yes, with cold-weather practices: Boise averages about 71 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 Idaho?
In Boise, June–September. In Pocatello, July.