Sierra Weather

• Weather notes - 2021
• Weather notes - 2019

Forecasts

• National Weather Service - Sierra zone forecast

• Blue Sky daily runs

When to go? It depends on what kind of snow year it is, and what kind of weather you prefer. August is by far the most popular time to be in the Sierra. If you want ideal weather, this is the month. If you want to avoid people, this is not the month. I have only twice had trouble getting a walk-in permit, but if it is going to happen, entering on a Saturday in August has the highest odds of yielding disappointment. Looking at when I did my last 22 trips from 2004 to 2019, I see:

• June - 1 trip
• July - 5 trips
• August - 10 trips
• Septermber - 5 trips
• October - 1 trip

Here is a crude summary of the seasons in the Sierra, adapted from Secor's introduction:

• Winter Winter begins with the first major storm (the first storm with snow that fails to melt). This is typically in mid November, but can be mid-October through mid-January. Typical winter weather is relatively mild, with nights dropping to 15 degrees F.
• Spring Spring lasts from late April to June. Note that winter storms are still a possibility. Some people feel this to be a superb time to visit the Sierra, as long as you are experienced with snow and well equiped.
• Summer Summer lasts from the end of June through mid-September. Early summer yields lots of mosquitos (and wild flowers!)
• Autumn Autumn lasts from mid-September till the first major winter storm (typically mid-November). In many ways this is the best time, with crisp, cold nights, no mosquitos, and few people.

(From supertopo.com)

• May - Only in low snow years will climbs be easily accessible. In general, most of the approaches will be snow-covered and many of the access roads may not be plowed. May is mostly dry but expect a few storms. There are no crowds in May.
• June - Aside from a rare storm, June is usually dry with warm temps and nice long days. Most of the access roads are plowed but there will still be snow on most approaches. Thunderstorms begin to develop so keep a close eye on the weather. The crowds start showing at the end of June and it becomes more competitive to get overnight camping permits. Charlotte Dome and Temple Crag are usually the first climbs to easily access.
• July and August - Prime Sierra climbing weather. Temperatures are hot at the trailheads but perfect on the climbs. This is also prime thunderstorm season so watch the weather closely. There are lots of crowds and it is competitive for overnight camping permits (get reservations at least a month in advance).
• September - Still great climbing conditions but the nights are cool. Some north-facing routes may be uncomfortably cold in the shade. The crowds start to thin out.
• October - Shorter days and cold nights mean less people. Climbing in the shade is no fun. Weather is mostly dry but the first winter storm can arrive late in the month. Easy to get overnight camping permits.
• November - Frigid nights and short days keep most people out of the High Sierra. Winter storms begin to arrive more frequently. A rare time to get some solitude before the heavy snow sets in.
• December - April Got skis? Frequent winter storms and icy temperatures make the High Sierra only accessible to those that enjoy suffering. In exceptionally dry years, during a warm spell, you may be able to run up one of the peaks in-a-day in December.

Data!

There is a single key number to get from their website, namely what percent this years snowpack is of normal (As of June 1, the 2009-2010 winter snowpack was estimated at 143 percent of normal). Look at the yearly summaries to find this figure,

"Normal" is a 50 year average. Secor discusses these numbers and says that in a 43 percent year he could easily cross passes in mid-June without an ice-axe, whereas in a 205 percent year a large cornice made crossing the same pass very difficult. In a 100 percent year most passes crossing the Sierra crest will be more or less snow free by July 1.

Manual stations just provide snow depth (usually monthly), Satellite stations give temperature, snow depth, usually daily or even hourly.

• CDEC home page
• CDEC snowpack data

• Bishop Pass 11200 feet (satellite)
• Charlotte Lake 10400 feet (satellite)
• Big Pine Creek 9800 feet (satellite) -- always cold
• - Bench Lake 10600 feet (manual - snow depth)
• - Piute Pass 11300 feet (manual - snow depth)

Here are a couple of temperature plots from the Charlotte Lake Station:

The first (below) shows the average air temperature for the year of 2009.

The second (below) also shows a 1 year period, but beginning and ending in the last week of May (which happens to be when I got intrigued by this data).

Here are 6 years of snow depth data (from November 2004 to May 2010 - that is a far back as the online data for this station allows). The snowfall the last 3 years looks quite similar. The 2006-2007 winter was a mild one, but the two before that were more severe.

Here are the snowfall records for the year of 2009. By late May, the snow was gone at this station. The first storm, in October, dropped a foot of snow.