Actually really interesting video from the creators. This model uses radio occultations, the space satellites integrate temperature, pressures and humidity . From what I understand, they compare the GFS with spire, and the one of the errors in the GFS is it consistently miscalculates MB by up to 10mb, which causes swings in the run to run consistency.
idk, its worth a watch.
https://video.search.yahoo.com/search/video?fr=mcafee&p=spire+weather+model+free&type=E210US739G0#id=1&vid=9701711166f0876451987a28b96876e3&action=click