Post date: May 9, 2017 4:06:28 AM
Straight from the horse's mouth--or the YNP website:
General Conditions
After one of the wettest winters in Yosemite history, spring has arrived with warming temperatures and a host of challenges for backpackers in the wilderness. Despite rising water levels from spring runoff, 4-7 ft of snow persists at 7,500 ft with 10 ft or more at the higher elevations. The snowline has crept up to roughly 7,000 ft but is still widely variable depending on aspect and topography. With such abundance, snow will linger well into the summer months, especially at higher elevations.
Increasing water levels from spring run-off will make many streams and creeks difficult or impossible to cross. This is further complicated by steep snow banks that persist on either side.
With the heavy rain and snow this winter, some trails may have more erosion damage than usual. Trails may have also experienced mudslides, rockfalls, and/or multiple downed trees. Exercise caution when traveling on trails and turn around if you do not feel comfortable going forward.
Winter travel techniques and skills are a must if you wish to backpack in Yosemite over the next few months. Be prepared for near-freezing temperatures at night and variable temperatures during the day. Except for the lower elevations and exposed areas, plan to camp in the snow. Springs storms can come at any time with heavy snowfall, making travel and navigation very difficult. Always be sure to check a current weather forecast before you start your trip and be prepared for a multitude of conditions.
Summer Outlook: Yosemite has received the most precipitation in its recorded history his winter (water year from Oct-Sept). However, the overall 2017 snowpack is only the 4th wettest on record in Yosemite and 176% of average. How can this be? Many of the storms this winter were relatively warm, meaning that while snow fell at the higher elevations it rained at lower elevations where it often times snowed in the past. This bears out in the snowpack with an uneven distribution of snow. The higher elevations, approximately 8,500 ft and above, are about 215% of average and are the highest on record, whereas the lower elevations are only 150% of average. Hence, the overall average of the snowpack is not a record.
It bears repeating, don't let the overall snowpack number average fool you. At elevations at 8,500 ft and above, this year is the highest on record! This Wilderness ranger echoes what the park hydrologist says, that it would be 'overly optimistic' to think about hiking easily in the higher elevations until August.
The recent May 1 snow surveys further reiterated this trend where most of the snow courses 8,500 ft and above were 215% or more of average. The two highest elevation courses are the also the highest percentage at 230%. The percentage of snow for the time of year stayed consistent or even increased a little compared to the April 1 snow survey, meaning there was no significant melt in April.
Spring weather will determine the amount of snow on the trails in July and August. A warm & dry spring will promote snowmelt whereas a cool & wet spring will diminish snowmelt. The chances of a warm, normal or cold spring are roughly equal, meaning a 33% chance for each. To make a significant change in the snowpack, the spring will have be particularly warm and sunny, making it even less likely. Spring weather can be highly variable and with any weather, it is unknown what it will be in the coming months.
So far spring has been cooler and wetter than normal, with April having above normal precipitation and below normal temperatures. Despite a few warm days so far in May, the weather is forecast to be cooler with the potential for precipitation for the next week.
For summer trips, be prepared for a different than usual hiking experience. Expect snow on the trails at elevations above 8,000 ft well into July and even August. There will likely be high creek crossings, snow on the trail and you may have to alter your route significantly depending on the conditions. Creek crossings in particular maybe challenging because if the creek is too high there are few options to cross and you may have to turn around.