San Francisco

Surface temperatures of the nearby Pacific Ocean remain chilly year round - in the mid-50s. In contrast, the California landmass is often much warmer. Onshore flow sets up, and as air moves over the Pacific toward land, water vapor within it cools, condenses, and forms a dense deck of fog. (NASA/Windows on Earth)

It's not always the clear days that give us the best images of Earth from the International Space Station.

Sometimes, the cloudy days can be even better for weather enthusiasts, because International Space Station astronauts capture images of our planet that reveal how weather conditions are created. Weather can be affected by terrain or other factors, as you can see in many of the photos above.

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The images are part of a project called Windows on Earth, created by Dan Barstow, in affiliation with the Technical Education Research Centers, Virtual High School, CASIS and the Association of Space Explorers. Barstow recognized the passion of ISSastronauts to take incredible photos of Earth from miles up and began compiling collections, sorting them into neat little pages that are easy to browse.

Here's how it works. The astronauts use Windows on Earth and other mapping tools to determine what landmarks the ISS is passing over, then they hone in on specific photography targets. The astronauts then look down on Earth through a set of windows known as the Cupola to get those amazing shots you see on Twitter or elsewhere.

Back on Earth, NASA downloads those images, and Barstow pulls the best photos and posts them to the Windows on Earth website. Images that feature weather patterns or clouds get their own webpage, which has become an instant hit with weather geeks.

To see the full collection of photos from the ISS, be sure to check out their website. You can find the weather photos on the home page, by clicking on the "Clouds" gallery.

Image captions written by weather.com meteorologist Chrissy Warrilow.