Infrared (IR): (color relates to temperature) - images from satellite radiometers that measure longwave or 'thermal' radiation (wavelengths of 12 micrometers or less) emitted from the earth and cloud surfaces. This measured radiation is proportional to the temperature of the earth or cloud surface. Typically, the white areas of an image represent cold or high altitude clouds, while the darker areas represent warm features, such as a cloud-free land surface that is heated by the sun. These images can be used at night, unlike visible satellite imagery that requires sunlight to be viewed.
Visible (Vis): (color relates to reflectivity/brightness)- this image displays reflected solar radiation (sunlight) from earth and cloud surfaces. Since visible imagery relies on sunlight, it can only be helpful when used during the day. The most reflective surfaces are seen as white (e.g., thick clouds, snow cover), while darker areas reflect less and absorb more radiation (e.g., oceans, vegetative surfaces). These visible images are particularly useful for viewing detailed surface features (e.g., snow cover, fog and thin clouds) because IR sensors are unable to decipher boundaries of features with similar IR temperature emission.
Water Vapor: (color relates to moisture) - this image senses moisture content in the atmosphere. The sensors detect infrared radiation (wavelengths typically near 6.7 micrometers) that is sensitive to absorption/re-radiation by water vapor molecules in the atmosphere. White areas signify moist layers, while dark areas represent dry layers. These images are used to forecast precipitation, winds (jet stream location), atmospheric circulations, hurricanes, storms, and other useful variables. For more information, please see: Water Vapor Imagery Tutorial.
For more information see: Interpreting Weather Satellite Images.
Greenwich Mean Time or GMT is the time standard against which all other time zones in the world are referenced. It is the same year round and is not effected by Daylight Savings Time. GMT is the north-south meridian at zero degrees longitude, or the "prime meridian", that runs through the Greenwich Observatory near London, England (where the system originated). GMT is used synonymously with Z (Zulu time), which stems from the military ("Zulu" is the radio transmission articulation for the letter Z). GMT is sometimes used interchangeably with UTC (Universal Time Coordinated). UTC or UT (Universal Time) is based on an atomic clock, and is therefore not exactly the same as GMT, which is based on mean solar time, but the difference is very small. UTC replaced GMT as the time standard, but GMT is still widely used today.
|GMT||Eastern Daylight Time
|Eastern Standard Time
|Central Daylight Time
|Central Standard Time
|Mountain Daylight Time
|Mountain Standard Time
|Pacific Daylight Time
|Pacific Standard Time
|Difference (in hours)||- 4||- 5||- 5||- 6||- 6||- 7||- 7||- 8|
|00||8 PM||7 PM||7 PM||6 PM||6 PM||5 PM||5 PM||4 PM|
|06||2 AM||1 AM||1 AM||12 AM||12 AM||11 PM||11 PM||10 PM|
|12||8 AM||7 AM||7 AM||6 AM||6 AM||5 AM||5 AM||4 AM|
|18||2 PM||1 PM||1 PM||12 PM||12 PM||11 AM||11 AM||10 AM|
Colorado: Mountain Standard Time (MST in the northern hemisphere Winter) is 7 hours earlier than GMT and Mountain Daylight-Savings Time (MDT in the northern hemisphere Summer) is 6 hours earlier than GMT.
Return to Weather
Send suggestions to Staff
Special thanks to Scott Bachmeier, Research Meteorologist and Wx-weenie friend,
Space Science & Engineering Centre, for his comments.
Note: the Boulder Laboratories Library does not necessarily endorse the views, facts, services or products on any off site links.