The El Nino/Southern Oscillation (ENSO) has been studied extensively for its impacts upon climate. The Multivariate ENSO Index is considered by many meteorologists to be the best overall measure of the strength of El Nino/La Nina. I have correlated the monthly MEI table with all of the monthly snowfall data I have collected through April 2006, and results are shown below. The MEI table is updated monthly with about a 1.5 month lag.
The monthly correlations are not large enough to have much predictive value. But by combining 6 consecutive months together to form seasonal data, the correlations for some areas get into the 50% range. This fits with observed experience that in big El Nino or La Nina years the expected effects occur from time to time but not consistently.
So I considered the seasonal correlations to be the main criteria in classifying areas. Not all areas provide
complete November to April data, and I would like to have 20+ seasons to draw conclusions. For areas without enough
complete seasons I looked at the monthly correlations, but also at the seasonal ones for nearby areas with many
complete seasons. For example Sugar Bowl is likely to be affected similarly to nearby Donner Summit and Alpine Meadows.
Another good example of why 15% range seasonal correlations are nothing to get excited about is a comparison of Alta and
Snowbird. Their correlations look different but I can't see any reason why underlying El Nino/La Nina effect would
vary between two areas a mile apart. The differences are just statistical noise.
El Nino strongly favors only Southern California, Arizona and far southern Utah, with milder effects extending to the southern
Sierra and New Mexico. It may surprise people how small the correlations are at Tahoe and in southern Colorado. Everyone
remembers the record Sierra snow during the record El Nino of 1982-83. But the 3rd and
4th strongest El Ninos (1992 and 1987) were severe drought years at Tahoe, and there are several good La Nina seasons, probably
assisted by colder temperatures minimizing low elevation rain. The most southwestern locations in Colorado (Purgatory, Telluride
and Red Mt. Pass) have even smaller correlations than North Tahoe.
La Nina strongly favors Washington State and inland areas ranging as far north as Revelstoke/Banff in Canada and as far south as Jackson Hole. Oregon and Colorado's farthest north area Steamboat are mildly favored, and there are scattered areas in the Northern Rockies of both U.S. and Canada that are only mildly or minimally effected. I was somewhat surprised that the snowiest Vermont areas (Jay, Smuggler's Notch, Stowe) are mildly favored by La Nina, while most other eastern areas are minimally affected. The other surprise is that coastal British Columbia is not that sensitive. I believe the Whistler base numbers are misleading because it had so much snow during the big La Nina years of the early 1970's. It has not done so well during more recent La Ninas due to global warming effects of more rain at its low 2,000 foot elevation. Whistler shows minimal La Nina sensitivity up at 5,000 or 6,000 feet, and the same is true for Mt. Washington on Vancouver Island at 4,000. Note that the Valdez/Thompson Pass area of Alaska slightly favors El Nino.
The Northern Rockies contain a few microclimates that are less sensitive. First would be Grand Targhee, which is the most consistent area that I track and doesn't seem sensitive to anything. Sun Valley and Sun Peaks have fairly dry climates that are blocked out of some prevailing weather patterns. It is well known that Sun Valley gets its biggest dumps from the south, and the record El Nino of 1983 was its second highest snow season. I suspect Red Mt. favors El Nina quite strongly even though it doesn't show up in my relatively sketchy data for the area. Big Sky's insensitivity is the other surprise, although Big Sky's weather tends to be independent of other areas.
With the exceptions noted above (Brian Head and Steamboat) El Nino/La Nina have minimal predictive value for Utah and Colorado ski areas.
Examination of the 12 strongest seasons of El Nino and La Nina show that the negative effects are fairly consistent, tending to lower snowfall an average of 10-15% during the unfavored condition. Positive effects tend to vary with the strength of the El Nino or La Nina episode. In El Nino years the only big destination resorts that are favored are Mammoth and Taos, with both of those in the mild category. For the numerous areas that are not favored, my general advice to avoid advance bookings until sufficient snow is on the ground should be taken more seriously, particularly where average snowfall is modest and there is less margin for error. See my lists of U.S. and Canadian Northern Rockies areas for reference. High snow areas like Jackson, Fernie and Steamboat are probably still just fine during their normally prime months of January and February. In La Nina years the favored northern resorts are more likely to be covered by Christmas as well as getting extra snow through the season. Mammoth is likely still good for mid and late season, but earlier bookings should wait until snow is on the ground. Taos takes until nearly February to get fully covered in normal years, and skiers should be more wary during La Nina years.
The data I acquired for Las Lenas in 2005 and Portillo in 2007 support the prevailing view that the high Andes are strongly favored by El Nino. Advance bookings to South American ski areas should be avoided in La Nina years until snow is on the ground. Australia/New Zealand have been reputed to have the opposite sensitivity, but in 2006 I acquired data for 3 South Island New Zealand areas that show little El Nino/La Nina impact. Spencer's Creek snowpack data does show that Australia is favored by La Nina.
|Strongly favored by El Nino||Minimal sensitivity to El Nino/La Nina|
|Southern California Composite 7,000 - 8,000||23.6%||53.9%||32||Sugar Bowl, Calif. 7,000||13.2%|
|Arizona Snowbowl 1, Ariz. 9,500||21.9%||54.7%||16||Monarch, Colo.||10.2%|
|Brian Head, Utah 9,770||19.5%||48.1%||16||Wolf Creek, Colo. 10,642||10.1%|
|Arizona Snowbowl 2, Ariz. 10,800||19.5%||47.6%||17||Aspen Mtn, Colo. 11,190||8.4%|
|Portillo, Chile 9,400||44.9%||38||Heavenly Valley, Calif. 8,400||8.0%||34.2%||22|
|Las Lenas, Argentina 7,400||18.7%||44.4%||22||Heavenly Valley, Calif. 10,000||6.2%|
|Alpine Meadows, Calif. 7,000||6.1%||17.1%||37|
|Mildly favored by El Nino||Sun Valley, Idaho 8,800||5.4%|
|June Mtn, Calif. 8,700||19.8%||Loveland, Colo. 11,200||5.1%||1.7%||26|
|Taos, N. Mex. 11,200||14.5%||29.3%||35||Central Sierra Snow Lab - Boreal, Cal. 7,200||4.5%||13.7%||41|
|Thompson Pass (Chugach), Alaska 2,450||12.6%||38.1%||20||Kirkwood (Carson Pass), Calif. 8,526||4.5%||14.4%||33|
|Mammoth Mtn, Calif. 9,600 or 8,900||11.1%||27.4%||39||Purgatory, Colo. 10,000||4.4%|
|Sugarloaf, Maine 3,695||4.3%||8.0%||41|
|Red Mt. Pass, Colo. 11,090||4.3%||-9.4%||17|
|Mildly favored by La Nina||Squaw Valley, Calif. 8,000||3.5%|
|Spencer's Creek, Australia 5,903||-25.8%||53||Beaver Creek, Colo. 11,200||3.5%|
|Whitewater, B. C. 5,500||-11.9%||Winter Park Base, Colo. 9,265||3.4%||0.0%||15|
|Steamboat, Colo. 9,200||-12.4%||-29.6%||24||Arapahoe Basin, Colo. 10,820||3.3%||6.4%||20|
|Smuggler's Notch, Vt. 1,600||-13.1%||-24.6%||15||Telluride, Colo. 11,170||3.1%|
|Cannon Mt., N. H. 1,800||-13.3%||-24.2%||31||Snowshoe, W. V. 4,848||3.0%|
|Stowe, Vt. 3,950||-13.5%||-28.6%||41||Remarkables, New Zealand 5,203||2.8%||-4.4%|
|Big White, B. C. 6,200||-14.6%||-36.4%||22||Red Mt. 2, B. C. 6,650||2.4%|
|Crater Lake (Mt. Bailey), Ore. 6,800||-15.2%||-29.4%||41||Mt. Hutt, New Zealand 4,602||2.3%||1.9%|
|Stevens Pass, Wash. 4,061||-15.7%||Squaw Valley, Calif. 6,200||2.0%||-40.2%||17|
|Mt. St. Anne, Que. 2,000||-15.7%||Alyeska, Alaska 1,400||1.1%||7.7%||25|
|Mt. Bachelor, Ore. 6,350||-16.2%||-27.0%||34||Mary Jane at Winter Park, Colo. 10,800||0.6%||3.4%||32|
|Mt. Norquay, Alb. 5,350||-16.3%||-32.7%||20||Mt. Rose, Nev. 8,600||0.4%|
|Loon, N. H. 2,000||-16.4%||Snowmass, Colo. 11,000||-0.1%|
|Jay Peak, Vt. 3,000||-16.7%||-32.6%||26||Gothic, Colo. 9,400||-0.6%||3.8%||31|
|Waterville Valley, N. H. 3,000||-0.7%|
|Strongly favored by La Nina||Alta, Utah 8,650||-1.5%||3.7%||39|
|Mt. Hood Meadows, Ore. 5,400||-12.1%||-47.8%||18||Brighton, Utah 8,740||-4.8%||-7.7%||36|
|Fernie Snow Valley, B. C. 5,400||-15.1%||-49.1%||19||Vail, Colo. 11,250||-1.5%||-0.8%||13|
|Lake Louise, Alb. 6,700||-16.9%||-38.2%||38||Big Sky, Mont. 8,920||-1.7%||-15.2%||17|
|Schweitzer, Idaho 4,700||-17.5%||Killington, Vt. 4,142||-2.3%||-4.9%||41|
|Snoqualmie Pass, Wash. 3,000||-19.1%||Snow Basin, Utah 7,700||-2.7%|
|Jackson Hole, Wyo. 8,250||-19.5%||-47.4%||40||Coronet Peak, New Zealand 4,032||-2.9%|
|Mt. Fidelity (Selkirks), B. C. 6,150||-20.0%||-48.5%||38||Sunlight, Colo.||-3.0%|
|Mt. Baker, Wash. 4,300||-20.3%||-53.2%||17||Mt. Washington, B. C. 3,926||-3.1%|
|Bridger Bowl, Mont. 7,100||-20.8%||Keystone, Colo. 11,641||-3.4%|
|Teton Pass, Wyo. 8,000||-21.3%||Northstar, Calif. 7,800||-4.0%|
|Sunshine Village, Alb. 7,028||-23.2%||-55.9%||37||Berthoud Pass, Colo. 11,315||-4.1%||-6.4%||36|
|Mt. Rainier Paradise, Wash. 5,420||-23.5%||-46.9%||41||Whiteface (Lake Placid), N. Y. 3,660||-4.3%|
|Silver Star, B. C. 5,200||-24.2%||-48.9%||18||Stratton, Vt. 3,875||-4.5%||19.0%||18|
|Whistler Base, B. C. 2,200||-26.3%||-48.5%||37||Tod Mt. (Sun Peaks), B. C. 6,100||-4.6%|
|Big Mountain, Mont. 6,700||-28.4%||Copper Mtn, Colo. 11,000||-5.0%|
|Park City 2, Utah 9,280||-5.2%|
|Crested Butte, Colo. 10,150||-5.2%|
|Blackcomb, B. C. 5,002||-5.3%||-8.4%||17|
|Mt. Snow, Vt. 3,600||-5.6%|
|Whistler Roundhouse, B. C. 6,000||-6.4%||-3.8%||28|
|Aspen Highlands, Colo. 11,100||-6.7%|
|Sugarbush, Vt. 3,000||-8.1%||-2.6%||20|
|Grand Targhee, Wyo. 8,200||-8.3%||-17.6%||31|
|Crystal Mtn 2, Wash. 6,100||-10.5%|
|Crystal Mtn 1, Wash. 4,400||-10.8%|
|Breckenridge, Colo. 11,100||-10.8%|
|Mt. Washington, N. H. 6,262||-11.0%||-21.9%||41|
|Snowbird, Utah 10,000||-11.9%||-18.9%||34|
|Deer Valley, Utah 8,200||-12.0%|