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
Know before you drive: FogCast checks the conditions that produce photogenic fog
Get more than a snapshot of current conditions. The LightCast app unlocks everything to plan ahead
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.
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.
Don't waste a sunrise drive. Check FogCast before you leave.
Download on the App StoreGreat Sand Dunes National Park sits in the San Luis Valley, a broad flat basin at 2,300 meters elevation surrounded by the Sangre de Cristo Mountains to the east and the San Juan Mountains to the west. The high desert basin sees surprisingly frequent radiation fog in fall and winter: cold air drains off the surrounding mountains and pools in the flat valley floor, and when humidity is sufficient after rain or snowmelt, dense fog forms over the dunes before sunrise.
When fog fills the San Luis Valley, the dunes rise from the mist like a desert island, with only the upper dune crests and the mountain backdrop visible above the white layer. Medano Creek in spring sometimes produces a similar layered effect with water vapor rising from the creek spreading across the dune base. The main dune field viewpoints near the visitor center offer the most direct compositions.
Fall and early winter are the best seasons for fog at Great Sand Dunes, from October through December. The San Luis Valley's flat basin geometry is ideal for radiation fog formation, and the combination of the dunes, the Sangre de Cristo backdrop, and fog is one of the more unusual landscape photography subjects in the country.