In this political season, flip-flopping is generally seen as a pejorative, but in the world of long-distance hiking, it's actually a derived strategy for completing thru-hikes that are a bit more nuanced than simple point to point hiking, and which offer some interesting possibilities.
Over lunch today, I allowed my imagination to be indulged. Suppose I had a corporate sponsor to do the Triple Crown over the hiking seasons of 2017, 2018 and 2019 respectively. How would I do them? I decided that each of the long trails actually merited a flip-flop. So how would I do it, if this is what I'd do, and why?
Summer 2017: The Appalachian Trail. My initial reason for wanting to do a flip-flop on this trail is the infamous party atmosphere of the so-called People's Trail, or the Social Trail as it's also sometimes called. Because there's a huge surge leaving Springer Mountain in mid-April, I'd start at Harper's Ferry at... I dunno, probably about that same time, and head north, before coming back to Harper's Ferry and heading south. Harper's Ferry isn't literally the center of the trail, but it's often considered to be so for spiritual and symbolic reasons, since it's the headquarters of the Trail's Conservatory, and it's close enough to the geographical center to make everyone shrug and just say why not (it's actually probably closer to about 2/5s of the way through, so it's a bit shy.) However, there are some other advantages that I didn't really consider. 1) There's no rush to get to the end. For most thru-hikers, getting to the peak of Katahdin before the park closes for the season can actually be a challenge. With my itinerary, I'd arrive right in the middle of the season. Plus, I can actually take as long as I'd like, because there's much less of a rush, if any at all, to even finish the hike. I can hike at my own pace near the end. Although by then, I imagine that my pace would be pretty good after the better part of five months or so of walking. 2) This also avoids the plague of black flies up in the New England portion. And it minimizes the risk of ticks, for that matter, too. 3) As the weather starts to turn more autumnal, I'll be in the south, heading southbound from Harper's Ferry again, so I really get the best of the climate at all stages of the hike, without ever having to deal with the hottest weather in the worst spots for that, or the coolest weather at the worst time for that. It truly optimizes the hike based on the climate as well. 4) It also starts the hike at a relatively easy and flat area. When I hit the difficult "Rocksylvania" portion of the hike, I'll be plenty warmed up, but not yet at all beat down by fatigue. I'll hit the 100-mile Wilderness and White Mountains stretch (which compared to conditions in the West isn't nearly as wild or remote or rugged as all that anyway) while I'm also still (relatively) fresh.
The average time to completion for an AT thru-hike is about 5½ to 5¾ months, which if I start in mid-April would have me finishing at the beginning of October. I don't know about what my pace would be like, but I don't intend to try and beat anyone, that's for sure. I despise being in too much of a hurry during this kind of activity. But I don't want to drag it out either. I predict 5½-6 months with up to 6½ or so at the absolute longest.
Summer 2018: The Pacific Crest Trail. Although the surge from Campo, CA is nothing like the surge from Springer Mountain, GA, it exists, and it's growing very, very quickly as awareness of the PCT has grown. Just in the last five years, the number of permits issues to thru-hikers has more than tripled, and it's estimated by the PCTA that about 50 hikers start their hike at the southern terminus every single day of April and a few days into May. For climate reasons, i.e. southern California gets really hot and dry if you wait any longer than that, but would still be prohibitively cold and snowy at higher elevations if you started any earlier, that's really the only thing that you can do. But once you hit Kennedy Meadows or so and start the High Sierras, you often have to wait on snow-melt. On the flip-side, you're often racing against potential snowfall that blocks your access to the northern terminus in early October. This could be avoided if I jumped the Sierras up to Ashland, OR, and then hiked northward to the terminus, avoiding high elevations (and latitudes) during the portion of the season that they're at risk of being snow-choked, as well as leaving the crowds (hopefully) behind. After hitting the northern terminus, I'd need to go back to Kennedy Meadows and doing the highest portion of the Sierras while it's still early enough that snow is not a significant risk. I may well get snow in Northern California while I'm finishing up, but my chances of it being really bad, or of being prohibitive to my goal of finishing the hike are much lower this way. Plus, like I said, hopefully I get to leave the surge of hikers behind and not worry about finding them again.
Although the distance is greater than the AT by almost 500 miles, the average time to complete it is 5 months. It's actually an easier, more well-groomed trail to hike, by report, so you can tend to make better time day to day. Plus, by then after having done the AP the season prior, I'll probably be walking longer, faster days on average just by virtue of being more in shape.
Summer 2019: The Continental Divide Trail. The CDT doesn't yet have a surge to speak of. There are still relatively few people who are willing to take on this beast, which is not even complete in every section, which doesn't yet have an "official" route for all areas, which means that a lot of variation is common, and which lacks much of the infrastructure that AT or even PCT hikers might take for granted. In part, because of this, the actual length is under a bit of dispute. According to Wikipedia, the length is another 500 miles longer even than the PCT, but lowball estimates as low as 2,500 exist, and the most reports indicate that the "typical" hike (depending on exact route chosen) is actually probably comparable to doing the PCT. As with the PCT, a start in mid-April heading NOBO from the Mexican border is generally seen as ideal, and as with the PCT, there are constraints that have to do with seasons and altitude. With the PCT, you may be facing lingering snowpack when you hit the Sierras, with the CDT, the same thing happens with the San Juans (at about the same elevation and latitude, curiously.) As with the PCT, if you go to long you'll get stranded in potential snows in the mountains near the Canadian border, so you can't be too slow.
The secret for this trail is, I believe, to pay attention to conditions. Some years, there may be snows still in the San Juans when you arrive, but the north might be drier, in which case flipping to the northern terminus and finishing the trail SOBO at Cumbres Pass, or somewhere thereabouts. But if could be the other way around; the San Juans might be drier and clear early enough to pose no problem, while the northern or central portions of the trail might be clogged. Unlike on the PCT where after the Sierras, you encounter (relatively) lower elevations, you still have big sections of reasonably high elevations all through Colorado, and through portions of northern Wyoming too, for that matter. It's a little harder to flip-flop the trail in a way that consistently avoids the risk of either lingering snowpack in the early season or early snowfall in the late season. It just all depends on the year in question and what happens that year.
Although it might not be a bad idea to skip the from the San Juans to somewhere in the middle of Wyoming if the snow isn't so bad in the Winds. Go back to Cumbres Pass and continue hiking NOBO, and you'll end the season in the Red Desert. Water availability might be an issue, but weather shouldn't be. Water in the Red Desert is a challenge no matter what, but at least you'll end the hike at a relatively low elevation, and early snowfall should be an insignificant risk. But the CDT is the one most likely to avoid a flip-flop entirely, or to do a more simple flip-flop where halfway through you drive up to the northern terminus and finish the hike SOBO.