Understanding Grayline Propagation
By NP4H Mission Control
Grayline propagation happens around sunrise and sunset, where the boundary between daylight and darkness can support long-distance HF contacts.
Low bands such as 40m, 80m and sometimes 160m can benefit from grayline conditions. DX stations that are difficult during normal hours may become workable during this short window.
NP4H operators should watch sunrise and sunset paths and try calling during those transition periods.