Like you, I have a similar chart on my wall, and was also mystified about those canted lines in the midwest (where I live by the way) for several years. No-one could tell me what they were, either. Then one day the cleaning lady came in and rolled up the venetian blinds, and the lines disappeared. It was a miracle!
Do you also live in the midwest?
I have a JNCA-5 Jet Navigation Chart, which is on the wall of my office, and which I use for general planning/dreaming.
In addition to the lines I recognize - lat/long, isogonic/anogonic, Canadian/Mexican FIRs, etc., there is a grid with lines about 120-150 nM apart, canted about 20 degrees to lines of lat/long in the midwest. The more east-west (horizontal) lines have arrows pointing west.
Can anyone educate me as to what these are?
I think I know what those lines are:
when the St. Andreas fault will kick in in California each line represent a 0.1 magnitude larger wave, e.g.: 8.0 is the first canted line on your map on the west, 8.1 is the second line, etc. About 1,000 nm west of the first line will be the new coastline of the Pacific Ocean. Beachfront property.
Where can I get one of those maps? I have no venetian blind and no cleaning lady, so I’m not worried about “ghost” lines, or their disapperance will not affect my planning/dreaming. Mostly dreaming.