The defining feature of a southbound thru-hike is the pressure to get through the Sierra before it snows. It's about 1,900 miles from the US/Canadian border to the end of the Sierra. On a bad year where Northern Washington isn't safe until mid-July and there is late September/early October snow in the Sierra, the hiking window could be as little as 75 days. On a good year when you can be in Washington before July 1st and the Sierra is safe until mid or late October, the window could be 100 days or more. This variation is entirely out of your control. It's impossible to know the duration of the hiking window in advance, but for planning purposes an educated guess might be the middle ground, hiking those 1,900 miles in about 90 days.
Part of the fun of thru-hiking is accepting that success is not guaranteed, and being able to adapt when things don't go as planned will be a necessary skill on trail.
Nevertheless, a wonderful feature of a SOBO thru-hike is that you'll be able to enjoy one of the best seasons in the Sierra Nevada. The crowds will be gone in late September/early October, there won't be any mosquitoes, stream crossings will be easy, and it's likely you won't find any snow on the ground even at Forester Pass.
What's so risky about that? Severe cold weather, harrowing wind and rain storms, and the possibility for early season snow.
Fall SNOW IN THE SIERRA
A defining part of hiking southbound is the pressure to get through the Sierra before fall snow storms. Especially in towns in Northern California, residents will be discouraging hikers and saying "you're late aren't you?" Well here's the data.
The "First Snow" column lists the first snow storm of the year near Forester Pass. In an average year there will be nine inches of snow that falls on October 11th near Forester Pass, and takes around four days to fully melt. Only one of the past 10 years (2009) did the snow accumulation continue until spring. The "Winter Accumulation" column lists the date when snow starts piling up that will not melt until spring.
General trail wisdom says to be through the Sierra by mid October on a southbound thru-hike. While this data shows that to be wise advice, it also points out that if you are an experienced winter backpacker and are prepared to weather a snow storm (and have food, the correct gear, and warm clothes), those first storms might only waylay you for a couple of days.
A hugely important part of this data is the large variation between snow years. In 2016 there wasn't a big snowstorm for the entire month of October. In 2011 there were 21 inches of snow on October 6th.
This points to an important lesson - As you get close to the Sierra, especially in the great resupply town of South Lake Tahoe, start paying very close attention to the weather. You may be able to see these storms coming, and plan your trip accordingly. If you can wait in a nearby trail town for three or four days while a storm passes, you might be safe in the Sierra through late October.
"General, widespread, and unwarranted panic that passes up and down the trail by word of mouth"
- Fear tornado (noun) definition
While this is not a phenomenon unique to the Sierra, beware! Fear tornadoes can cause a hiker undue stress as everyone on trail gets caught up in panic and paranoia. For example, someone will post a photo on Facebook of an early September snow storm at South Lake Tahoe and all of the southbounders will freak out! Then the snow melts the next day but no one posts a photo of the melt. Or NOBOs will tell tales of blow downs near Crater Lake that are terrible and the worst ever and SOBOs will all worry. Turns out they are much less difficult than the ones SOBOs faced in Northern Washington. The same thing happens when SOBOs warn NOBOs of bad stream crossings in Washington, when in fact the crossings are easy compared to what the NOBOs faced in the Sierra.
Beware again! Sometimes the fear is justified, and some trail news is real and can help you avert danger. This is especially true as it gets later in the season in Northern Washington and the Sierra. Pay special attention to forecasts, and check the weather before leaving town and starting a section. Also pay attention to the details of a storm. How many inches did it snow? What are the temperatures on that part of the trail over the next week? What's the weather forecast in that area?
COLD WEATHER in the Sierra
While the snow is pretty variable, it's almost guaranteed that you'll deal with some very cold weather between South Lake Tahoe and Southern Kennedy Meadows.
By this point most SOBOs will be carrying very light packs, especially after warm weather in Northern California. It's worth the weight to add some warm clothes for safety, and to avoid getting caught without the proper gear in a dangerous weather situation. In late September and early October snow can fall almost anywhere, and a lesser known danger are strong rain and wind storms, a topic covered below.
During October in the Sierra the weather will likely be below freezing at night, cold in the morning, and warming up in the daylight to 35-50 degrees. Expect the weather to be below freezing every night in the High Sierra, between Tuolumne Meadows and Forester Pass.
Below is temperature data from Mammoth Lakes, CA. IMPORTANT NOTE - This data is from Mammoth Lakes at 8,000 feet, and can't be seen as representing actual conditions on the trail.
To reiterate that point, this table is warmer actual conditions on the trail. From experience Mammoth Lakes is often much warmer than the PCT, and 8,000 feet is about the lowest elevation you reach in the Sierra.
Fall Rain and Wind Storms
While snow gets the headlines, extreme rain and wind storms can be life threatening, especially on the exposed ridgelines between South Lake Tahoe and Tuolomne Meadows. This year one SOBO had to get off trail during a torrential storm near Sonora Pass. This is a hiker who had already walked 1,500 miles of the trail, and then was forced to stop his hike. The same storm that's hardly noticed if you're protected by tree cover can be severely dangerous on an extended ridgeline. Few (if any) rain jackets can keep you dry when rain and snow are blowing at speeds 40+ mph. And once you are wet and cold without an option for cover, your life is in danger. A group of four SOBOs were struck by a storm like this on top of Mt. Baden-Powell in So Cal, and only a nearby parking lot and a ride from a friendly trail angel avoided the specter of an unsafe night. There aren't as many options for a safe exit near Sonora Pass.
This is an especially difficult challenge because of the abrupt weather changes in September. On Sept 15th it might be 80 degrees in Mt. Shasta, CA. Two weeks later it could be near freezing as you cross Sonora Pass. Temperatures vary widely during September and early October, so keep an eye on the forecast as it gets later in the year. The simplest way to do that is to check the weather forecast for the nearest trail town. It's not an exact science, but it will give you an idea of possible temperatures/weather events. And importantly, pack clothing appropriate for the forecast.
While NOBOs have ample opportunity to resupply in the Sierra, SOBOs have to deal with rapidly closing resupply points and long hitches or side trails to get more food. As a SOBO you'll have to do a bit of planning so you’re not stuck somewhere without food staring at a "store closed" sign. Here's a quick list of what you can rely on during a usual year, from north to south.
- Sonora Pass - If weather is good, you can get a resupply from Sonora Pass Resupply without leaving trail. Hikers normally love this company and they provide a great service to NOBOs and SOBOs. You can also hitch to Bridgeport (very far, super tough hitch) or Northern Kennedy Meadows (closer, better option).
- Tuolumne Meadows - Closes in late September (and may return packages to sender a few days before they officially shut). If the store is closed you can hitch (about an hour drive) down to Yosemite Valley, where they have a large, reasonably priced grocery store that is open late in the season. This can be a long hitch also.
- Red's Meadow - The shuttle from Red’s Meadow to Mammoth Lakes stops running around Labor Day. Red's Meadow Pack Station (with a store and restaurant) closes near the beginning of October.
- Muir Trail Ranch - Almost certainly closed for the season before a normal SOBO gets there. Closes early September.
- Vermillion Valley Ranch - Normally stays open until the second week of October, but the ferry closes down so you'll have to walk all the way to the ranch. They post updates on Facebook about their status.
- Kearsarge Pass - 10 miles north of Forester Pass, and 90 miles north of Southern Kennedy Meadows, you can take a 7.5 mile side trail up and over Kearsarge Pass to the Onion Valley parking lot. From there (you might have cell service) you can call for a ride down to Independence, with bus access to Bishop or Lone Pine.
- Southern Kennedy Meadows - Almost guaranteed to be open and fully stocked. Great place. Time to celebrate!
After the Sierra you'll enter Southern California. Read more about water shortages and other dangers by clicking below.