so ive been paying more attention to solar flux lately trying to figure out when to actually bother getting on HF. been using a couple of the online tools to track SFI and K-index but honestly i still dont really understand how to read what im seeing well enough to predict anything useful. like yesterday the SFI was up around 165 or so and i figured 10m would be ripping but i heard basically nothing from europe when i was on around 1400 UTC. then i took a break, came back at like 1700 and worked 4 stations in spain and one in italy without any issue. so what am i missing here. is there some other factor i should be looking at or am i just timing it wrong. i know gray line is a thing but i thought that was more of a morning deal

also noticed the K-index jumped up to 4 yesterday evening and things got pretty noisy on 17m which i sort of expected, but 20m seemed totally fine? that felt backwards to me. still learning how all this fits together

yeah propagation is one of those things where you think you've got it figured out and then the bands just do whatever they want anyway. the SFI number is useful but its really more of a general indicator of how ionized the F layer is, doesnt tell you about the actual path geometry between you and wherever you're trying to work. a 165 SFI is great but if the MUF for that specific path hasnt quite made it to 28 MHz yet you'll sit there and hear nothing. the thing i always tell people is to check something like VOACAP or even just DXmaps to see if anyone nearby is actually completing contacts on the band before you assume it's open to the region you want

the K-index thing with 20 vs 17 being affected differently isnt that weird actually. higher bands tend to suffer first when there's geomagnetic activity but sometimes the disturbance hits certain latitudes harder and if your path to somewhere on 20m is more equatorial it might skate under it. grey line is definitely not just a morning thing either, there's an evening component too and some paths are actually better in the evening grey line depending on where the other end is

im kind of in the same boat honestly, just got my general last spring and have been trying to get into DX chasing. the solar flux stuff feels like trying to read tea leaves sometimes. i did stumble onto a site called prop.kc2g.com that shows real time ionosonde data and that helped me a little bit more than just looking at the SFI number alone, might be worth checking out if you havent already. still figuring it out myself though so take that for what its worth