History of Mammoth and Sierra Nevada Snow Conditions

The History of Southern California Snow Conditions chart is the best expression I've devised for displaying the range and incidence of snow conditions. In order to construct such a chart it is necessary to have week by week reports of conditions. The snowfall data that I collect is monthly and not sufficient for this purpose. Through personal knowledge I only have sufficient info for Southern California and Mammoth.

The focus of these charts is to show coverage of terrain and frequency/consistency of packed powder snow that has not been through a melt/freeze. The weekly grades are not a measure of fresh powder, which cannot be predicted in advance for a specific week. In 2008 I derived a method to estimate percent of powder days from monthly snowfall. I now apply that percentage to all weeks rated A or B and show that percentage and an adjusted total grade at far right. For details, see What Is the Probability of a Powder Day?
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The Mammoth chart would be very boring in its entirety, so I show here the 25th, 50th and 75th percentiles, plus 5 extreme seasons in each direction of my experience.

Definitions:
A:
Powder/packed powder on at least 50% of terrain. Generally 90+% of terrain open, but 50-60% in very early or late season if nearly all of the upper mountain is covered and skiable. 3 points for an A weekend in the charts below.
B:
50-80% open with mostly packed powder, or 90+% open with less than 50% packed powder. 2 points for a B weekend in the charts below.
C:
20-40% open. If this seems generous, consider that 20% of Mammoth is 700 acres and 2,100 vertical, which would be full operation at Mt. Baldy in Southern California or Stowe in Vermont. 1 point for a C weekend in the charts below.
HISTORY  OF  MAMMOTH  SNOW  CONDITIONS  
Pwdr Adj
Season/Month October November December January February March April May June July Total A B C Pwdr Total
1982-83 C 1 C B A A 9 A A A A 12 A A A A A 15 A A A A 12 A A A A 12 A A A A 12 A B A B B 12 B C C C 5 C C D D 2 92 25 30 37 26% 127
2004-05 B B 4 B A A A 11 A A A A 12 A A A A A 15 A A A A 12 A B A A 11 A A A B B 13 A B B B 9 C C C C 4 C 1 92 23 32 37 26% 127
1981-82 0 C C A A A 11 A A A A 12 A A A A A 15 A A A A 12 A A A A 12 A A A B 11 B B B B B 10 C C C C 4 B 2 89 23 30 36 19% 114
1994-95 D D D D 0 D C B A 6 A A A A 12 A A A A A 15 A A A B 11 A A A A 12 A A A B B 13 B A B B 9 C B C C 5 C C C C D 4 87 21 29 37 23% 115
2010-11 0 D C A 4 A A A A 12 A A A B A 14 A A A A 12 A A A A 12 B A B A 10 B B A B B 11 B B C B 7 B 2 84 20 29 31 29% 118
75th percentile 0 D D C B 3 A A A A A 15 A A A A 12 A A A A 12 A A A A A 15 A A B B 10 B B B B 8 C C C C 4 C 1 80 20 27 33 19% 102
Median 0 D D C 1 C B B B A 10 A A A A 12 A A A A 12 A A A A A 15 A B B B 9 B C C C 5 C 1 0 65 15 22 28 15% 78
25th percentile 0 D D 0 D D C C B 4 B B A A 10 A A A A 12 A A A B B 13 B B B C 7 C C C C 4 0 0 50 9 17 24 10% 56
2011-12 0 D D D 0 D D C C 2 D D D C B 3 B B B B 8 A B A A A 14 B A B C 8 C C C C 4 0 0 39 5 13 21 9% 43
1986-87 0 0 D 0 D B C C 4 C A A A 10 A A A A A 15 B B C C 6 D D 0 0 0 35 8 11 16 10% 40
2013-14 0 D D D D 0 D D C C 2 D D D D 0 C B B B 7 A A B B A 13 A B B B 9 C C C C 4 0 0 35 4 12 19 7% 38
1990-91 0 D 0 D D D D C 1 C C D D 2 D D D D 0 A A A A A 15 A B B B 9 B B C C 6 0 0 33 6 11 16 13% 38
2014-15 0 D D D 0 D C B B 5 C C C C 4 C R C C 3 B C C C C 6 C C C D 3 D C C C 3 0 0 24 0 3 21 4% 24
Squaw Median 0 D C 1 C C B B B 8 A A A A 12 A A B A 11 B A B A B 12 B B B C 7 C C D D 2 0 0 53 9 19 25 17% 64

Results/Comments:
Mammoth's strongest point is snow preservation. The average percent of terrain that is packed powder/winter snow is 78% mid-March and 58% first of April. And only 8 of the past 38 seasons were majority spring conditions mid-March. Snow preservation also results in staying open to Memorial Day in 95% of seasons and 4th of July in the top 30%.

Mammoth has some favorable attributes in early season also. Average snowfall is high, it almost never rains, lower slopes are mostly intermediate and the steep upper slopes often get extra blown-in snow. Thus about 75% of terrain is usually skiable on a 3-4 foot base. Working against early season reliability is the well known volatility of Sierra snowfall. If an extended dry spell hits in November/December, the early season can be very restricted. In the worst quarter of seasons full operation will be attained mid-January or later.

The extreme seasons illustrate the snowfall volatility. In 2004-05 Mammoth had a 56-inch dump Oct. 20-22 and only staffing considerations prevented the entire mountain from opening immediately. In 1981-82 and 1982-83 October snowfall was more modest, but it continued into November so full operation was still attained well before Thanksgiving. In 1982-83 it snowed every week from mid-January to mid-May, producing an incredible 25 weeks (half a calendar year!) with powder/packed powder conditions. 1994-95 has the record for both October 8 earliest opening and August 13 latest close. But that October snowfall was also modest and the first big dump was in late November. 2010-11 had season record snowfall but the big dumps did not start as early as 2004-05, 1981-82 or 1982-83. The early July snowpack in 2010-11 was the best I have ever seen and Mammoth closed by management decision even though the snow lasted for a few more weeks.

On the negative side 1986-87 and 2013-14 are examples of Mammoth not getting its first major dump until February. 1986-87 looks worse mainly because Mammoth did not have snowmaking then, and now it has a sizeable reservoirs and a portable system that can be used where it's most needed. In 1990-91 the big dumps did not come until March, but the March snowfall was 176 inches so the late season was as good as a normal year. 2011-12 had a January storm that opened about 3/4 of terrain but full operation was not achieved until early March as in 1991. In 2013-14 the storm that opened most of the mountain was about 3 weeks later than in 2011-12. Some of the 1991 vs. 2012 and 2014 comparison can also be attributed to early season snowmaking. 1975-76 was before my time but had to be similar to 1986-87 based upon snowfall incidence. 1976-77 was nearly a total wipeout, with no snow before New Year's, only 90 inches January to March, then 3 feet in May. 1976-77 probably would have scored in the 10-15 range. 2014-15 was the second lowest season to 1976-77, and also only the second time the mountain was never 100% open. However, December was the snowiest month and that plus snowmaking kept Mammoth at least half open through March, albeit rarely with winter packed powder conditions.

Other Sierra Ski Areas
So how do Lake Tahoe resorts compare? The Sierra Crest west of Tahoe gets about 20% more snow than Mammoth, so the snowiest areas Kirkwood, Sugar Bowl and Alpine Meadows have an early season profile as good as Mammoth's with the extra snow offsetting Mammoth's higher altitude/no rain advantage. The biggest areas Squaw Valley and Heavenly are slower to get fully open than Mammoth due to lower snowfall at Heavenly and much higher coverage needed (6-8 feet) on Squaw's expert skewed terrain. Squaw's median is shown accordingly. Squaw is 2,000 feet lower than Mammoth with a lower percentage of north facing slopes, so spring conditions develop much earlier. I show the median as a "checkerboard pattern" of alternating A's and B's starting mid-February. This does not imply that the A weeks are better than the B weeks. It shows that you can expect spring conditions if it hasn't snowed recently, but that snowfall is still abundant until April when the chart shows all B's. Also keep in mind that the high snowfall variability applies throughout the Sierra, so the high and low seasons may be as far from the median as at Mammoth.

More Snow Conditions Charts
Vermont
Fernie and Whistler
Utah
Colorado