First: I'm not a real pilot. I used an on-line flight planning tool, and in the brief was the following "GPS NOTAM":
GPS 11/032 ZSE NAV (CHLK GPS 15-15) GPS (INCLUDING WAAS, GBAS, AND ADSB)MAY NOT BE AVAILABLE WITHIN A 476NM RADIUS CENTERED AT 360822N1173846W (BTY214059) FL400-UNL DECREASING IN AREA WITH A DECREASE IN ALTITUDE DEFINED AS: 432NM RADIUS AT FL250, 375NM RADIUS AT 10000FT, 340NM RADIUS AT 4000FT AGL, 253NM RADIUS AT 50FT AGL. DLY 2130-2230 1511172130-1511182230
I must admit I don't understand most of this, but it seems like GPS is unavailable in what seems to be a huge inverted cone of space. What's going on here?