My '01 blazer ahs the overhead temperature display. I've noticed sometimes when the outside temperature is around or below freezing just under the number it will have "ICE" displayed when I first get in and crank it but shortly it goes away. What is this?

 

Just a warning that the temperature is sufficiently low to support the formation of ice.

 

Why does it show then goes away but the temp hasn't changed?

 

Because it is just a temporary warning.

 

If it stayed on you wouldn't be able to see your direction of travel or the temp.