Water vapor imagery is used to analyze the presence and movement of water vapor moisture in the upper and middle levels of the atmosphere. The wavelength spectrum used to detect water vapor is in the 6.7 to 7.3 micrometer wavelength range. The upper and middle levels of the atmosphere are from about 650 mb to the top of the troposphere. Above the troposphere there is very little moisture.
A dark color or warm color indicates a relative lack of upper level moisture. It does not mean though there is a lack of moisture in the lower levels or at the surface. It could be very moist at the surface or it could be fairly dry. A white or cold color indicates a high concentration of water vapor.