When viewing weather on this NOAA page, please be advised that the base lodge elevations are much lower and the summit of Mammoth Mountain is over 1,000' higher and weather both lower and higher can be very different.
Open Snow is an online collection of meteorology hobbyists, each of whom focuses on different parts of the country - this site tends to have great maps and information.
On this site, you will find real-time weather data (temp, wind, humidity, and other) both at Main Lodge and at the Mammoth Mountain summit.
Howard Sheckter is a long-time local prognosticator who is well-known both around town and abroad as a meteorology hobbyist and enthusiast..
The Mammoth Mountain website is a tremendous source of local information, not only for the daily ski report and weather, but for many other mountain and local activities, too.
This is the weather blog of longtime Mammoth local Steve Taylor. His site has current weather information, recent photos, and many links to other weather sources.