Although VOAPROP and similar propagation predictors work well at determining the HF propagation and likelyhood of a path over a range of 2000miles plus they do not seem to cut the mustard for >1000mile paths. This is not quite the same as NVIS “Near Vertical Incidence Skywave” where we generally think about ranges of 100miles max. Within the UK and into Europe, it has also been interesting how, from one day to the next, propagation on 40m /60m has fluctuated during the past summer.
I think the factors affecting this mode of propagation are the critical frequency (now available almost instantaneously on line) and the D layer absorbtion.
Is anyone aware of a programme that takes these and possibly other factors, into consideration when determining the likelyhood of a path and band?