NASCAR coverage from Phoenix International Raceway will move from NBC to NBCSN at 6 p.m. ET.
The Quicken Loans Race for Heroes 500 was scheduled to begin at 2:41 p.m. ET on NBC, but persistent rain showers have left the start of the race in a holding pattern.
As of 4:15 p.m. ET, track drying was continuing on the 1-mile oval with more rain threatening.
It generally takes about 45 minutes to an hour to dry the Phoenix track.