Satellite Weather

Infrared

Clouds — Infrared satellite imagery measures the temperature of the reflecting surface. Cold objects appear white, and warm objects appear dark. Generally, high clouds are cold and appear white, and warm land or oceans appear dark.

Airport Locations — Selected airport locations are depicted using the four-letter ICAO identifier at the location.

Infrared satellite imagery measures the temperature of the closest reflecting surface as observed from the satellite. Geosynchronous satellites are in orbit 22,500 miles above a fixed point at the earth. Clouds appear white in the image; the brightness of the cloud depends on the temperature of the cloud. Higher clouds, which are colder, appear bright white. Lower clouds, which are warmer, appear gray. Land and oceans appear gray or black in the image. The warmer the temperature of the land or water, the darker the feature looks on the image.

Infrared satellite images can be viewed 24 hours per day, since the temperature is being measured. Land temperature varies between night and day, which can be seen in IR satellite images taken at night versus during the day. Very low clouds, such as stratus and fog, are sometimes difficult to see in IR imagery, as the temperature is very close to the nearby land temperature.

Maps are valid at different intervals, depending on the satellite. Generally, images are taken every 15-30 minutes for GOES imagery, every one-three hours for GMS imagery, and every three-six hours for Meteosat imagery. Map valid time indicates the time the image was taken. Maps are created generally 15-30 minutes after the valid time of the image.

Visible

Clouds — Visible satellite imagery sees the earth as the human eye would see it. Clouds appear white or gray, and land or oceans appear dark. Generally, thick clouds appear white, and land or oceans appear dark.

Airport Locations — Selected airport locations are depicted using the four-character ICAO identifier. Green circles might also appear on some regional maps at the airport location.

Visible satellite imagery is a picture taken by the satellite. Therefore, it needs sunlight on the viewing surface for anything to be seen.

For this reason, visible satellite images are only useful during daylight hours. Visible images show various clouds and land features very differently than infrared images. Clouds that appear bright white are thick and are reflecting sunlight. High, thin clouds appear opaque, whereas low clouds — such as stratus and fog — appear quite bright. You can also see terrain features in the land in visible images, so that mountains and forested areas appear darker than desert or farmland areas. Snow-capped mountain ranges and ice packs also appear white and are sometimes difficult to differentiate between clouds. Visible images are best viewed during the middle of the local day when the sun is at the highest azimuth.

Maps are valid at different intervals, depending on the satellite. Generally, images are taken every 15-30 minutes for GOES imagery, every one to three hours for GMS imagery, and every three-six hours for Meteosat imagery. Map valid time indicates the time when the image was taken. Maps are created generally 15-30 minutes after the valid time of the image. Visible images are only created during local daylight hours.

Satellite/Radar Composite

Base Reflectivity — 16 levels depicted with colors from dark green (very light) to red (extreme) that indicate the intensity of precipitation. Legend associates colors with intensity.

Severe Thunderstorm/Tornado Watch Areas — Yellow box indicates a Severe Thunderstorm Watch area. A red box indicates a Tornado Watch area. Watch areas represent areas where the conditions are favorable for the development of severe thunderstorms or tornadoes.

Surface Freezing Line — Solid light blue line depicts the 0 degree Celsius isotherm at the surface. Areas north of the line are below freezing, and areas south are above freezing. The line can be used to approximate where snow versus rain is falling. Snow can fall at temperatures above freezing, and a rain/snow mixture can be present near the line or in mountainous areas.

Airport Locations — Selected airport locations are indicated on the background map by using the four-letter ICAO identifier in white.

This map combines Infrared Satellite imagery with NEXRAD Radar Base Reflectivity. The valid times for the satellite image and base reflectivity might not be exactly the same because as the data does not always coincide, but they are normally within 30 minutes of each other.

Maps are available every 15 minutes and contain the latest GOES IR satellite image combined with the latest NEXRAD Base reflectivity mosaic. Radar mosaic is typically more current than the corresponding satellite image.