FogCast · Mount St. Helens, WA
Fog Forecast for Mount St. Helens
Know before you drive: FogCast checks the conditions that produce photogenic fog
Reading current conditions…
🔒 App Exclusive
The full FogCast forecast is in the app.
Get more than a snapshot of current conditions. The LightCast app unlocks everything to plan ahead
- 📈 Full FogCast score (0–100)
- 📅 7-day fog outlook
- 🌅 Best photography windows
- 🔔 Push alerts when conditions improve
- ⭐ Save favorite locations
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7-day free trial · $2.99/mo
Why fog is hard to predict
Humidity alone isn't enough. Wind alone isn't enough. Cloud cover alone isn't enough. Photogenic valley fog requires several conditions to line up at once, and most weather apps don't read them together.
Dew Point Depression
When air temperature and dew point converge below 2°C, the air is near saturation. This is the single strongest fog predictor and the first thing FogCast checks.
Wind Speed
Fog needs calm air. Below 5 km/h is ideal. Above 15 km/h, fog disperses before it can pool in the valley. A standard weather app won't flag this combination.
Overnight Sky Clarity
Clear overnight skies let the ground cool rapidly, pushing surface temperatures toward the dew point. Counterintuitively, clouds overnight suppress radiation fog.
Temperature Trend
FogCast reads the overnight temperature arc. If temps are converging toward the dew point hour by hour, fog probability increases significantly by pre-dawn.
Check today's FogCast
What the app shows you
Full FogCast score, fog type, chase-or-skip verdict, and 10-day outlook — all in the app.
Get LightCast Suite on iOS
Get notified instead of checking every morning
Set a FogCast threshold once. The app will alert you when conditions at your saved locations look promising, so you're not manually checking at 4am.
⏰
Wake up only when conditions look promising
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Avoid wasted drives when fog never forms
⭐
Save your favorite photography locations
🌫️
Never miss a rare dense fog event
Fog photography at Mount St. Helens
Mount St. Helens rises to 2,549 meters in southwestern Washington, a dramatically truncated volcano that lost its upper 400 meters in the catastrophic 1980 eruption. The surrounding landscape of blast zone, Spirit Lake, and old-growth forest is frequently visited by fog systems moving inland from the Pacific, and the contrast between the raw volcanic terrain and soft fog creates photography that is unlike any other location in the Pacific Northwest.
Spirit Lake, at 975 meters elevation, is the most powerful fog photography location. The log-covered lake reflecting the crater and dome through morning mist is one of the most iconic landscapes in Washington. Johnston Ridge Observatory at 1,268 meters gives direct crater views and is above the fog when valley inversions fill Spirit Lake valley. The Ape Canyon and Lava Canyon areas on the south and east flanks occasionally hold isolated fog patches in forested gullies. September and October are the most reliable months before heavy snowfall closes upper roads.
Mount St. Helens fog arrives in two forms: marine-origin advection fog moving up the Toutle River valley from the coast, and radiation fog forming in the Spirit Lake basin on calm, clear nights. The Spirit Lake radiation fog is the most photogenic — it requires calm overnight winds, clear skies, and a temperature drop to within 3°C of the dew point at lake level. If by midnight the lake basin is calm with humidity above 88%, a dense fog layer over the lake at dawn is highly likely.
Other fog photography locations
Frequently asked
Can I check FogCast on the website?
This page shows a preview of current conditions, including humidity, wind, temperature, and dew point. The full FogCast score, 7-day outlook, push notifications, and best shooting windows are available exclusively in the LightCast app for iOS.
Is FogCast free?
The current conditions preview on this page is free, no account needed. The full FogCast tool is in the LightCast Suite iOS app, which includes a 7-day free trial. After the trial it's $2.99/month, cancel anytime in the App Store.
Why use FogCast instead of checking humidity?
Humidity alone doesn't tell you whether photogenic fog is likely. High humidity with strong wind produces no fog at all. FogCast combines dew point depression, wind speed, overnight sky clarity, temperature trend, and visibility into a single score built specifically for fog photography planning.
What is FogCast's scoring scale?
FogCast scores fog conditions from 0 to 100. A score of 75 or above indicates dense fog is expected. 55 to 74 means fog is likely and worth chasing. 35 to 54 suggests patchy mist is possible. Below 35, conditions are unlikely to produce photogenic fog. The full score is available in the LightCast app.
