Which months and which hours, from Portland.
Mount Rainier, Mount Hood, Mount Baker, Mount St. Helens, Denali, The Olympics and Mount Angeles. Visible now or not, the five-day forecast, and the sunrise and sunset light. $1.99, one time.
From Portland the mountain is most reliable July through September, on the same days as Hood. It sits north-northeast of the city at about 50 miles and has a flat top, so it is easy to miss beside Hood.
The summit is 8,363 ft, nearly 3,000 lower than Hood. A cloud deck at 7,000 ft leaves Hood and Rainier standing above it and hides St. Helens completely, so on a marginal day check this page, not Hood's.
Longview, Castle Rock and the SR 504 road up the Toutle are the classic view, looking east into the crater from 30 to 35 miles. Sunset is the light there, with the sun behind you. Autumn inversions put Portland under fog with the mountain in sun above it, and the I-5 towns are often clear when Portland is not.
Reading the airports along the sightline.
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We read the cloud ceilings at the airports between Portland and the summit, the cloud layers at the summit from the MET Norway model, and whether that cloud sits below 8,363 ft. No crowd reports.
Cloud forecasts get less reliable the further out they go. Days four and five are drawn in six-hour steps for that reason, and the forecast stops at five.
Different weather stations, different sky. The same morning can be fog in one and clear in the other, twenty miles apart. Each region page reads its own stations.
Wildfire smoke and haze can hide the mountain on a day the cloud numbers say clear. When the numbers are unsure, the page says so.
Our pick for binoculars: Vortex Diamondback HD 10x42 on Amazon