If you’re flying the Great Falls area (KGTF) from now until March 6th, you’ll want to watch out for some GPS outages due to testing.
Right now, they’re testing daily from 1631z-20z, and the impact is all about how high you’re flying. You could lose WAAS, GBAS, and ADS-B.
See the ranges here:
If you do experience outages, you’re asked to only contact ATC if you’re in need of assistance, not to report any outages.
NOTAM INFO: NAV GPS (AFSMO GPS 18-04) (INCLUDING WAAS, GBAS, AND ADS-B) MAY NOT BE AVBL WI A 361NM RADIUS CENTERED AT 470259N1103758W (GTF115040) FL400-UNL, 302NM RADIUS AT FL250 222NM RADIUS AT 10000FT 213NM RADIUS AT 4000FT AGL 162NM RADIUS AT 50FT AGL.
The full FAA text is here: https://www.faasafety.gov/files/notices/2018/Feb/AFSMO_18-04_GPS_Flight_Advisory.pdf