Here is a question that perhaps requires a detailed seminar, but I'll post it anyway.
A typical backcountry trip typically starts with route and time planning, and a lot of it is based on the daily avalanche forecast provided by the regional avalanche centers. Sierra Avalanche Center, for example, not only provides a daily forecast but also hosts a resource where public and professionals report their observations, column test results photos and videos, which adds to the picture significantly. Unfortunately, there is a substantial area in Sierras that is not covered by any Avalanche Center, e.g., some parts of Stanislaus forest.
What data for pre-trip planning is available for backcountry tourers in such areas? Caltopo gives the initial general idea about the terrain, however, the weather, and its season history is also vital? What resources do you recommend? SNOTEL, weather stations, etc.?
I would look at NOAA, https://www.mountain-forecast.com, and Fat Map (really useful for slope angle and aspect as well as a bunch of other features) to try and get as much information about the weather that I can, but for stability info, maybe social media or reddit if someone has been there before.