I used the SAM tool's built-in downloader to get data for my location. It ended up coming from Station ID 891492, I guess. The data source appears to be NSRDB. I thought that this source included snow data, but when I go in the Shading and Layout page and check, "Estimate losses from snow coverage," I get the error message, "Weather file has no snow data. Simulation will fail."
Is there a way to overcome this for my location in the Chicago suburbs and include the snow losses?
From there, click the DOS link regardless of your operating system to download the .exe file.
After the file downloads, change the .exe extension to .zip. (This requires that your file browser is set up to make file extensions visible.)
Unzip the file -- the Zip archive should contain a .tm2 file.
Move the .tm2 file to your weather file folder, for example [user]/SAM Downloaded Weather Files. You can also rename it to something more recognizable than the station number, for example rename 26451.tm2 to anchorage.tm2
In SAM, on the Location and Resource page, choose the file from the Solar Resource library. If it does not appear in the library, try clicking Refresh Library, or Add/Remove Weather File Folders to add the folder containing the file so SAM can find it.
Look under "Weather Data Information" in the "Optional Data" section. If the file contains snow data, Minimum Snow Depth will be a number. If it does not contain snow data, it will be "NaN" for "not a number."
On the Shading and Layout page, under "Snow Losses" at the bottom of the page, click Estimate Losses from Snow Coverage.