Saw what appeared to be a piece of blowing trash at ~400' altitude and about ~60mph, but then realized conditions were calm.

Noticed a white/ish colored object of indiscernible shape moving in a slightly "wavering" flight path (as if being blown by the wind), at an average, slightly variable heading of ~240. My first impression was that it was a piece of blowing trash floating through the air, like perhaps a small plastic grocery bag. I then realized that conditions were completely calm (the KLAS automated weather station reports variable winds at speeds of 0 to 5 mph, consistently, between the times of 0540hrs and 1000hrs PST ). Upon looking away from the object to observe the wind speed, based on the trees and flags in my vicinity, I lost sight of the object and was unable to find it again. I estimated its altitude to be ~400ft, which would have put the speed of the object at an estimated ground speed of approximately ~60 mph; But I could not make out a specific shape of the object, so it's apparent low altitude, and thus it's ground speed, could have been an optical illusion (I derived said estimates based on an object obeying normal laws of physics). It is possible that the object was at a much higher altitude and ground speed. If it was at ~400' altitude, it's GPS location, at first sighting, would have placed it just north the intersection of University Center Dr. and E. Flamingo Rd., crossing squarely through the flight path of the 19R runway of McCarran Intl. Airport. However, if the object was actually at a much higher altitude, it could've been located generally over McCarran Intl. Airport, or possibly even south west of the airfield, and it's ground speed could have been as much as ~3.0 mach or higher. The strangest things about it were it's meandering characteristics: A non-linear flight path - variable speed, heading, and possibly altitude - as well as the fact that it was very difficult to "focus" on and discern a specific shape. Again, it most closely resembled a standard white, plastic grocery bag being blown by a stiff wind. It was not a bird. I am a sky watcher, and have extensive experience with detailed observation of birds & civil & military aircraft of all types, weather phenomena, and blowing trash (I live in Las Vegas), as well as thousands of hours in a very realistic and customized version of Microsoft Flight Simulator 2004. I have neither reported nor seen anything "UFO-ish" in my entire 52 years of life, so seeing & reporting something like this is in no way a regular occurrence for me.