An optical display, called 'sundog,' was visible just after sunrise Friday morning near Waterford in western Racine County.
Below is a picture sent to our office Friday morning by Jeff Shervey as he approached Waterfored about 8 am CST. Note the small 'rainbow' arc to the left of the sun. Sundog is the proper term for the small rainbow.
A sundog (parhelion) is an optical display of the sun's light being split-up into components as the sunlight passes through very small ice crystals suspended in the air. The splitting-up process is called refraction. The ice crystals can be at any altitude in the atmosphere. Sometimes the ice crystals will be part of a cirrus cloud.
We had a bitter cold, arctic air mass over Wisconsin Friday morning with minimum temperatures below zero at most locations. About 1,500 feet above the ground there was a thin layer of slightly warmer air called a "temperature inversion". Warmer air can hold more moisture than colder air. Therefore, any moisture in the temperature inversion probably precipitated out as ice crystals. Ice crystals of this nature are more likely only when low-level temperatures are in the single digits above zero degrees Fahrenheit or less.
Kapela, WFO Milwaukee/Sullivan