People sometimes become confused or frustrated when their weather app radar indicates precipitation that either is not falling, or is not falling at a rate suggested by the radar. The problem is that weather radar cannot depict precipitation perfectly or consistently because it is a remote sensing instrument. The radar beam leaves the radar site at an angle of half a degree. This means the center of the lowest scan from the Doppler radar in Mayville, N.D., is actually scanning the air at about 4,000 feet above Fargo-Moorhead and about 8,000 feet above Fergus Falls.
If the lower atmosphere is dry, significant evaporation can occur underneath the radar beam.
In addition, the type of precipitation being scanned - particularly the presence of ice at the level of the beam - can greatly affect the relative brightness of the radar echo, and therefore the precipitation display. All of this means that the colors of a radar display are a loose sliding scale of precipitation intensity.