Skip to main content.

If everything is working the plot you see here is the infrared sky temperature at my location plotted from midnight local time till the present. When the sky is clear of clouds the infrared sky temperature can be used to measure the amount of water vapor in the atmosphere. The blue plot is the infrared sky temperature. The red plot is the air temperature. It the sky temperature is siginificantly lower than the air temperature the sky is probably clear. If the temperatures are close to each other the sky is probably cloudy. Forrest Mims explored this approach for measuring water vapor and published an article in the "Bulletin of the American Meteorological Society" Measuring Total Column Water Vapor by Pointing an Infrared Thermometer at the Sky Plots for past days that have data avaliable can be viewed by selecting a date below.