Several people have either email or called and asked about the orange-red sun from earlier in the week. There have been forest fires in Montana and Idaho the past few weeks and on several days the smoke from these fires has been present over this area.
It was probably the thickest on Tuesday morning as the sun was coming up and it made for an eerie blood-red sunrise.
The fires in the Rocky Mountains, especially one of the larger fires just happens to be due west of the southern valley. The upper-level wind pattern has recently been in a zonal, or west to east flow pattern blowing the smoke over the area on several occasions.
Most of the time you may not have noticed, or just thought there were some higher level clouds over the area, but last Tuesday it was thick enough that some could even smell the smoke in the air.