Washington weather and outdoor projects
Western Washington, including Seattle, has a marine climate with mild, cloudy, damp weather from October to May and dry, mild summers. July through mid-September is the main window for staining and painting, because the rest of the year often brings long damp spells and short days.
East of the Cascades, Spokane and the Columbia Basin are much drier, with hot summers and cold winters. Moss and mildew grow readily west of the mountains, so clean decks and siding before coating them. Late-summer wildfire smoke can affect both sides of the state.
Frost dates in Washington
In Seattle, the median last spring freeze (32°F) is around March 2 and the median first fall freeze is around November 23, a frost-free season of about 266 days.
In Spokane, the median last spring freeze (32°F) is around April 26 and the median first fall freeze is around October 12, a frost-free season of about 168 days.
How Washington compares with other states
Seattle is tied for the most rainy days of the 50 state main stations (93 a year with 0.1 in or more). Seattle has the 2nd-fewest days at 90°F or hotter of the 50 state main stations (4 a year). Seattle is tied for the 7th-longest deck staining season of the 50 state main stations (5 good months).
| Measure (Seattle) | Value | Rank, highest first |
|---|---|---|
| Deck staining season | 5 good months | 7th of 50 |
| Frost-free season | 266 days | 8th of 50 |
| Freezing nights | 25 a year | 43rd of 50 |
| Rainy days | 93 a year with 0.1 in or more | 1st of 50 |
| Days at 90°F or hotter | 4 a year | 49th of 50 |
| Summer afternoons | 48% humidity at 3 PM, June–August | 31st of 47 |
Best time to stain a deck in Washington
In Seattle, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 59°F, Oct 61°F). November–March is too cold, with average highs around 50°F. April and October are cool, with highs around 60°F, so choose the warmest afternoons.
In Spokane, the most reliable months are June–September. May and October can also work on the right days (average highs May 67°F, Oct 58°F). November–March is too cold, with average highs around 40°F. In April, nights average about 37°F, too cold for the coating to dry and cure overnight. In May, nights average about 45°F, so finish early on mild days and check the overnight low. October is cool, with highs around 58°F, so choose the warmest afternoons.
Best time to paint outside in Washington
In Seattle, the most reliable months are May–September. February–April and October can also work on the right days. December–January is too cold, with average highs around 48°F. November averages about 13 days a month with a tenth of an inch of rain or more, which makes long dry stretches hard to find. February–March is cool, with highs around 52°F, so choose the warmest afternoons. In April, nights average about 43°F, so finish early on mild days and check the overnight low. October averages about 8 wet days a month, so wait for a clear stretch.
In Spokane, the most reliable months are June–September. April–May and October can also work on the right days (average highs Apr 57°F, May 67°F, Oct 58°F). November–March is too cold, with average highs around 40°F. April and October are cool, with highs around 57°F, so choose the warmest afternoons. In May, nights average about 45°F, so finish early on mild days and check the overnight low.
Best time to pour concrete in Washington
In Seattle, the most reliable months are April–October. November–March can also work on the right days. November–March brings about 5 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
In Spokane, the most reliable months are May–September. October can also work on the right days (average highs Oct 58°F). November–April averages about 20 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. October brings about 8 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
Best time to seal a driveway in Washington
In Seattle, the most reliable months are June–September. May and October can also work on the right days (average highs May 66°F, Oct 61°F). November–April is too cold, with average highs around 52°F. May and October are cool, with highs around 63°F, so choose the warmest afternoons.
In Spokane, the most reliable months are July–August. May–June and September can also work on the right days (average highs May 67°F, Jun 74°F, Sep 74°F). October–April is too cold, with average highs around 45°F. May is cool, with highs around 67°F, so choose the warmest afternoons. In June 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 Washington
In Seattle, the most reliable months are May–October. February–April and November can also work on the right days. December–January is too cold, with average highs around 48°F. February–April and November are cool, with highs around 54°F, so choose the warmest afternoons.
In Spokane, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 57°F, Oct 58°F). November–March is too cold, with average highs around 40°F. April and October are cool, with highs around 57°F, so choose the warmest afternoons.
How the weather differs across Washington
| Place | Hottest month avg high | Coldest month avg low | Rain per year | Last spring freeze | First fall freeze |
|---|---|---|---|---|---|
| Seattle | 78°F | 37°F | 39 in | March 2 | November 23 |
| Spokane | 84°F | 24°F | 16 in | April 26 | October 12 |
Of the places above, Seattle has the most good months for staining, painting and concrete combined (17 job-months), and Spokane has the fewest (13).
Monthly weather in Seattle
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 48°F | 38°F | 13 | 5.8 in | 72% | 7 |
| February | 50°F | 38°F | 9 | 3.8 in | 64% | 6 |
| March | 54°F | 40°F | 11 | 4.2 in | 60% | 2 |
| April | 59°F | 43°F | 9 | 3.2 in | 54% | 0 |
| May | 66°F | 49°F | 6 | 1.9 in | 52% | 0 |
| June | 71°F | 53°F | 4 | 1.4 in | 51% | 0 |
| July | 77°F | 57°F | 2 | 0.6 in | 46% | 0 |
| August | 78°F | 57°F | 2 | 1.0 in | 46% | 0 |
| September | 72°F | 54°F | 4 | 1.6 in | 52% | 0 |
| October | 61°F | 47°F | 8 | 3.9 in | 64% | 0 |
| November | 52°F | 41°F | 13 | 6.3 in | 71% | 3 |
| December | 47°F | 37°F | 12 | 5.7 in | 74% | 7 |
*Days with 0.1 inch of rain or more; column notes.
Monthly weather in Spokane
| Month | Avg high | Avg low | Wet days* | Rain | 3 PM humidity | Freezing nights |
|---|---|---|---|---|---|---|
| January | 35°F | 25°F | 7 | 2.0 in | 79% | 26 |
| February | 40°F | 26°F | 5 | 1.4 in | 64% | 23 |
| March | 49°F | 32°F | 7 | 1.8 in | 50% | 19 |
| April | 57°F | 37°F | 4 | 1.3 in | 40% | 8 |
| May | 67°F | 45°F | 4 | 1.6 in | 35% | 2 |
| June | 74°F | 51°F | 4 | 1.2 in | 33% | 0 |
| July | 84°F | 58°F | 2 | 0.4 in | 24% | 0 |
| August | 84°F | 57°F | 1 | 0.5 in | 23% | 0 |
| September | 74°F | 49°F | 2 | 0.6 in | 29% | 0 |
| October | 58°F | 38°F | 4 | 1.4 in | 44% | 8 |
| November | 42°F | 30°F | 7 | 2.1 in | 69% | 19 |
| December | 34°F | 24°F | 7 | 2.3 in | 79% | 27 |
Source: NOAA NCEI U.S. Climate Normals 1991–2020 for SEATTLE TACOMA INTL AP, SPOKANE INTL 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 Washington?
In Seattle, May–September. In Spokane, June–September.
When is the last frost in Washington?
Seattle: around March 2; Spokane: around April 26.
Can you pour concrete in winter in Washington?
Often, with care. Seattle averages about 20 freezing nights from December to February, so pick a mild spell, cover the slab on cold nights and keep it from freezing for the first 48 hours.
What months are best for sealing a driveway in Washington?
In Seattle, June–September. In Spokane, July–August.