I am planning a trip to Las Vegas for the last week of September 2012. It is easy to look up specific city weather but I am wondering about the roads to/from Las Vegas from the east (Ontario).

I am worried about the early snow or other hazardous risks (freezing rain / ice) at the higher altitudes. If I come in/out on Interstate 40 through Amarillo (Tx) / Albuquerque (NM)/ Flagstaff (Az) will I have any problems?

I may take other routes at the time but as long as there is a 'safe' route I will be happy.