About this planner

↓ Want the details? Keep reading.

What it's actually telling you

Every peak is coloured by one simple thing: out of the last 20 years, how often did it have a good-enough day to climb — for the time of year and weather pattern you've picked. A "good-enough day" here means little or no rain/snow, and not brutally cold (under about 3 mm of precipitation and warmer than roughly −15 °C overnight). Green = often, red = rarely.

Where the numbers come from

• 500 peaks all across Washington — the well-known list of the 100 highest peaks, plus 400 more from public maps so every part of the state is covered (Olympics, both sides of the Cascades, the northeast, and the Blue Mountains in the southeast).
• 20 years of daily weather (2004–2023) for each peak — rain, snow, and temperature — from Daymet, a free government weather dataset. That's about 7,300 days per peak.
• Wind direction for the same 20 years from NASA, used to tell what kind of weather day it was (a wet storm blowing in off the ocean vs. a dry, clear spell).

The clever bit: matching backups to the weather pattern

Not all bad weather is the same, and the best backup depends on which kind is coming. Washington's weather sorts into a handful of repeating patterns:

• Wet storms off the ocean (from the southwest) — about 1 in 5 days. These dump rain on the western mountains but the dry eastern side stays much better. Best time to head east.
• Dry, clear spells (wind from the northwest) — about half of all days. Nearly everywhere is climbable, so a backup barely matters.
• A few in-between patterns of lighter, mixed weather.

When you tell the tool which pattern you expect (or let the live forecast do it), it re-ranks your backups to match. That's why the same peak can send you east on a storm day but south on a dry day.

How the backup ranking works

For your chosen peak, the tool looks at all the past days when that peak had bad weather, then asks: on those exact days, which other peaks were still good? Those are your best backups. It's a real "if this is out, where should I go instead" answer, straight from the history.

One thing the data taught us

A backup is rarely a place that's good because your peak is bad — Washington's storms tend to be big and hit most of the mountains at once. So when your first choice is out, everywhere is a bit worse. The trick is finding the peaks that stay the least-bad — usually the dry country east of the Cascade crest. And this matters most in summer; in winter the storms are so widespread that hopping to a backup buys you much less.

The three planning windows

• About a month out — no real forecast exists that far ahead, so the tool shows you what's typical for that time of year.
• One to two weeks out — it pulls the live forecast and shows the likely pattern day by day.
• Two to three days out — the near-term days (highlighted) are the ones to trust when you commit.

Please keep in mind

• This is not a forecast for your climb day. The colours are the typical odds from the past 20 years. For an actual trip, use the live-forecast tab and always check a real mountain forecast.
• Good weather doesn't mean safe. The tool only knows about rain, snow, and cold. It knows nothing about avalanche danger, ice and snow conditions on the route, rockfall, wildfire smoke, or whether the road is open. A green peak can still be dangerous.
• It's a broad-brush picture. The weather data is averaged over roughly 1 km, so it misses very local effects. And the elevations for the 400 extra peaks are approximate.
• Where you draw the "good day" line is a choice. The rain and cold cutoffs used here are sensible defaults, but a rock climber and an ice climber would want different ones.

Sources

Weather: Daymet and NASA POWER (both free, public). Live forecast: Open-Meteo. Peak list: the Bulger List plus OpenStreetMap. Maps: Esri, OpenTopoMap, USGS. Built as a personal planning aid — always double-check against official forecasts and avalanche bulletins.