Why does this NOTAM make me think GPS is unavailable?
This outage is due to department of defense GPS interference testing taking place 17-18 Nov 2015.  The interference generated may make the GPS signal unreliable and the outage cone described by NOTAM lets you know that you can't trust the GPS signal during this time.  This interference may be purposeful jamming or live testing of devices that may interfere with GPS to ascertain what level of interference occurs.