I've added this page to the HFU, which estimates the skip zone around a transmitter site for 6925 kHz, based on ionosonde data from Wallops Island, VA:
http://hfunderground.com/propagation/nvis6925.htmlThere is also a link on the same page for estimates based off data from Boulder, CO.
The basics on how this is calculated is here:
http://www.radiohobbyist.org/blog/?cat=12&paged=3If you look at the graph for the estimates for yesterday (before the data scrolls off the left side), you'll see that the skip zone never disappeared. That's quite unusual for 43 meters, usually it does once the Sun is up and the ionosphere strengthens. Everyone I was in touch with online yesterday complained about how bad propagation was.
This data could be useful for listeners to see whether or not they're likely to hear relatively close stations. Likewise for operators in the reverse direction :-)