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The HAP chart is a guide to frequency selection for HF communications between mobiles and a specified base station, in this case WASHINGTON DC.
The recommended frequency for communications with the base at a given hour is read off from the point in the map corresponding to the mobile's location. The predictions are made from real time data which are updated each hour. "dash lines" - If present, these delineate areas of unlikely communication. Poor communication areas which can result from one or more of the following conditions:
-the Absorption Limiting Frequency (ALF) is higher than the Optimum Working Frequency (OWF).
-the ALF exceeds the highest frequency in the user's frequency set.
-there is no suitable frequency from the user's set that is between the OWF and ALF.
USA Region Real Time Ionospheric Map
Recent X-Ray Flare Events (From US GOES Satellite, NOAA)