Squamish is the great Pacific Northwest bouldering forest — Dreamcatcher, The Singularity, thousands of problems on high-friction granite scattered through cool conifer canopy at the base of the Chief. But the Sea-to-Sky sits under the wettest weather in Canada, and the bouldering window is narrower than the season looks. When should you actually book?
We replayed 30 years of real daily observations — weather AND observed daily snow depth — from the Environment and Climate Change Canada Squamish Airport station through the climbingforecast snow-aware drying model. Here's what the data says.
When is the best time to boulder in Squamish?
The numeric peak: July. 85% chance of a climbable day, and by early July the Pacific wet season is comfortably closed. August (84%) sits right behind. Cool mornings, warm dry afternoons, and enough consecutive dry days that even the shaded forest boulders have had time to lose the ambient damp. This is the summer plateau Squamish is famous for and the numbers back it up — zero RED days across the entire May-through-September window, so the constraint isn't wet rock, it's your own comfort in the heat.
The shoulder months: April, May, September, October. May (69%) and September (73%) sit at the strong end of the shoulder — cool crisp friction days on either side of the summer peak, popular with anyone chasing send conditions on the harder problems without August's warmth. April (54%) and October (50%) are the wet-season shoulders proper — usable if you're flexible, but expect nearly half your days AMBER while the forest clears between showers.
When to skip: November through March. 27–43% climbable days as Pacific frontal systems dominate Howe Sound. Squamish Airport records nearly 2,400mm of annual precipitation with most of it in this window, and observed snow-on-ground days (averaging ~22 per winter, sometimes 70+ in the coldest years) push the boulders firmly RED in cold snaps. If you want granite bouldering in winter, drop south to Skaha in the semi-arid Okanagan or further afield to Bishop.
Month-by-month conditions
| Month | Green Days | Amber Days | Red Days | % Green | Green + Amber |
|---|---|---|---|---|---|
| Jan | 8.3 | 12.8 | 9.9 | 27% | 68% |
| Feb | 12.1 | 11.6 | 4.5 | 43% | 84% |
| Mar | 13.0 | 16.8 | 1.3 | 42% | 96% |
| Apr | 16.2 | 13.8 | 0.0 | 54% | 100% |
| May | 21.4 | 9.6 | 0.0 | 69% | 100% |
| Jun | 21.4 | 8.6 | 0.0 | 71% | 100% |
| Jul ★ | 26.4 | 4.6 | 0.0 | 85% | 100% |
| Aug | 26.2 | 4.8 | 0.0 | 84% | 100% |
| Sep | 21.8 | 8.2 | 0.0 | 73% | 100% |
| Oct | 15.6 | 15.4 | 0.0 | 50% | 100% |
| Nov | 10.9 | 17.9 | 1.2 | 36% | 96% |
| Dec | 10.8 | 12.8 | 7.4 | 35% | 76% |
Based on 30 years of real daily observations (1995–2024) from the ECCC Squamish Airport station replayed through the climbingforecast snow-aware drying model. The RED days in Dec–Feb come almost entirely from the snow-aware logic — Dec 7.4 RED days is the model catching real cold snaps in the record. Grand Wall Boulders, Cacodemon and Crumpit Woods share drying-model parameters, so the three sectors return identical monthly numbers.
Summer works, winter doesn't
Summer works — and unlike sandstone destinations you don't have to hide from the heat. Unlike Fontainebleau, Rocklands or Albarracín — where hot rock kills friction and closes the sending window — Squamish granite is high-friction rock that handles warm days without damage. The table above shows zero RED days May through September: the model finds no genuinely-wet-rock days across the whole summer plateau. Daytime highs push into the high 20s and low 30s, so most people climb early or evening, swim at Alice Lake or the Cheakamus in the afternoon, and save hard sending for cooler shoulder-season sessions.
Winter is genuinely not a trip — and the snow-aware model now shows why. The Sea-to-Sky corridor is one of the wettest places in Canada, and the winter closure has two overlapping causes. The dominant one is rain: continuous Pacific frontal systems keep the forest canopy dripping, and the AMBER counts in Nov–Feb (12–18 days per month) are the model catching moisture that never fully clears between storms. The second cause used to be invisible to our forecast: snow. This rewrite uses real observed snow-on-ground from the airport record converted to SWE and fed to the model's snow accumulator, so the 7.4 RED days in December and 9.9 in January are real cold-snap events from the observation record, not a temperature-threshold guess.
Peak Potential
July delivers 85% green days plus zero surface-RED days — the top of a broad summer plateau. May through September stay at 69–85%; unlike sandstone, Squamish granite handles warm days fine, so the summer constraint is comfort not friction. Late June and September are the cool-friction picks for the hardest problems.
Wet-Season Shoulders
April (54%) and October (50%) are the transitional months as the wet season closes and reopens. Zero RED days but roughly half AMBER — usable if you're flexible and willing to wait out fronts. The forest canopy holds moisture for days, so a two-day dry window matters more than a single dry afternoon.
Rain-Dominant Winter
November through March return 27–43% climbable days. The 7–10 RED days per month in Dec/Jan are the snow-aware model catching real cold-snap snowpack from the airport observation record — not a heuristic. A winter Squamish bouldering trip is a bad bet.
How we calculated this
30 years of real daily observations (1995–2024) from the ECCC Squamish Airport station — real daily temperature, real daily precipitation, and real observed daily Snow on Ground. Observed snow depth is converted to snow-water-equivalent at ρ = 300 kg/m³ and fed to the drying model's snow accumulator, so the model's own thresholds (≥ 3 mm SWE → RED, ≥ 1 mm → AMBER) fire against real ground truth. Run against the Grand Wall Boulders, Cacodemon Boulders and Crumpit Woods sectors; they share drying-model parameters so the three-sector average is a clean "Squamish bouldering" number. ECCC data is Government of Canada open data under the Open Government Licence.
The same snow-aware methodology powers our Magic Wood, Val di Mello, Rocklands, Albarracín and Fontainebleau data pieces. It's not a substitute for checking the actual forecast the week you're going — but it's the honest answer to "when should I book?"
Good luck and enjoy the climbing!