Observations of HF signal powers on two circuits in North America have been compared with the values predicted by two HF propagation programs, Voice of America Coverage Analysis Program (VOACAP) and Advanced Stand Alone Prediction System (ASAPS). Neither program consistently provided the more reliable predicted signal powers. For the longer circuit considered (2820 km WWV Fort Collins to Hanscom Air Force Base), ASAPS was found to be the more accurate program for the lower frequencies (at night), while VOACAP was the more accurate for the higher frequencies (during the day). The RMS errors ranged from a few decibels to 15 dB. For daytime 7.335 MHz propagation on the 490 km CHU Ottawa to Hanscom Air Force Base circuit, the VOACAP RMS errors (~4 dB) were less than the ASAPS RMS errors (~8 dB). The errors for the two programs were very similar for 3.330 MHz propagation, peaking at ~9 dB just after sunrise and just before sunset and ~3 dB during the night.