What each picture shows

• GeoColor (true color by day, city lights at night): Looks like a photo from space in daylight. At night, clouds show from infrared heat (low clouds and fog blue-ish) over a picture of city lights. The best all-round view.
• Visible (sharpest detail, daytime only): Sunlight reflected off clouds, snow and smoke, at the finest detail (about a quarter mile). Watch for bubbling storm tops, outflow boundaries and fog burning off. Dark at night.
• Infrared (cloud-top temperature, day and night): How cold the cloud tops are. Colder means higher, so the brightest colors are the tallest storms. Works around the clock, which makes it the go-to view at night.
• Water vapor, upper level: Moisture high up (around 30,000 ft), even where there are no clouds. Shows the jet stream, troughs and spinning lows that steer storms. Dark is dry air, white and green is moist.
• Water vapor, mid level: Moisture in the middle of the atmosphere (around 20,000 ft). Good for spotting dry air wrapping into storms and the shape of weather systems.
• Water vapor, low-mid level: Moisture lower down (around 10,000 to 15,000 ft). Helps show elevated mixed layers, the warm dry "lid" that can hold storms back.
• Air mass (jet stream and dry intrusions): Colors air masses: red is dry sinking air from high up (often near the jet stream and strong lows), green is warm tropical air, blue and purple is cold polar air.
• Storm tops (sandwich, daytime): Visible detail layered with infrared color, so you can see both the texture and the coldest tops of storms. Overshooting tops and cold rings mark strong storms. Daytime only.
• Fog and low clouds (day and night): Separates low clouds and fog from high clouds. At night, fog and low stratus show as light blue-gray; helpful for early-morning travel and work.
• Fire hot spots: Highlights heat from fires: hot spots glow orange to yellow, hottest white. Best in daytime. Smoke plumes show better on visible or GeoColor.
• Lightning (GLM flash extent): Lightning seen from space by the Geostationary Lightning Mapper, counted over a few minutes. Shows where storms are electrically active, even over the ocean.

Which to use: GeoColor or visible by day, infrared at night, water vapor to see the jet stream and big storm systems that are still days away, lightning and storm tops when thunderstorms are going. Satellites see cloud tops from above; to see rain and hail under the clouds, use radar.

The two satellites: GOES-East sits 22,000 miles above the equator at 75° west, in line with the East Coast, and watches the eastern US, the Gulf and the Atlantic. GOES-West sits above the equator at 137° west, out over the Pacific, and watches the western US, Alaska, Hawaii and the Pacific. Both send a new US picture about every 5 minutes; the whole-Earth view every 10. Pictures appear here a few minutes after they're taken.