The information below is a combination of my comments, 35 years of experience forecasting the weather for various U.S. ski areas and excerpts from Tony Crocker’s informative ski site: bestsnow.net.
CORRELATION BETWEEN EL NINO EVENTS AND SKI WEATHER
El Nino/La Nina events are persistent weather patterns, but their effects upon ski area snowfall are less clear-cut. In my view, it is important to factor in both climate change and other teleconnection indices (not just El Nino/La Nina), in order to better construct more accurate weather forecasting methods for the ski industry.
According to Tony Crocker, “Correlations of various El Nino/La Nina values are not necessarily the best way to analyze El Nino/La Nina events and their associated snowfall potential for ski areas. Many meteorologists believe that only the stronger episodes have a material impact.
Shown below is Tony’s list of ski areas favored by El Nino, along with their monthly and season correlations to the MEI index and average snowfall during strong El Nino and La Nina months. Many of these El Nino events had very high (positive) AAM. It is in the cases when AAM is weaker and other teleconnections such as the MJO, Arctic Sea ice and other teleconnections play “at least” as important a role as El Nino/La Nina, that meteorologists must factor in these other climatic forcing mechanisms when making medium and longer term weather forecast predictions for the ski and many other industries.
According to Tony, for the best winter snows and ski conditions, El Nino strongly favors Southern California and Arizona, with milder effects extending to the southern Sierra, far southern Utah and New Mexico. In El Nino years, the only big destination resort that is favored consistently is Taos, and that in the mild category. 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. As the 2010-11 La Nina strenghtened these areas received almost no snow after August 1, 2010. Advance bookings to these lower latitude South American ski areas (also the Valle Nevado group) should be avoided in La Nina years until snow is on the ground.
He constructed graphs to illustrate the variability of the snowfall correlations to El Nino/La Nina. The one shown below is for selected areas favorable to El Nino.
Referring to the chart below, the horizontal axis lists the ski seasons since 1966-67 in order of strong El Nino at left to strong La Nina at right. The vertical axis is percent deviation from normal snowfall. The blue line is the sum of MEI indicies from OCT/NOV to APR/MAY, scaled to fit the graph.
The purple line shows the dramatic boost to Southern California snowfall from El Nino, with the 2 biggest snow years correponding to the 2 big El Nino of 1982-83 and 1997-98. 5 of the top 8 El Ninos produced at least 170% of normal snow. There are no guarantees even here, as the #3 and #5 seasons 2015-16 and 1986-87 were real stinkers at only 59% and 62% normal snowfall.
Moving to Taos, New Mexico (yellow line) the effect is less dramatic. The 2 big El Ninos were 116% and 118% of average, while Taos’ record 1972-73 season at 174% was in the 6th highest El Nino year. But only 2015-16 and 1991-92 of the top 7 EL Nino years was below average at Taos, and those were still 98% and 95% of average.
In the Sierra the picture is mixed. Everyone remembers the huge Sierra snow during the record El Nino of 1982-83. But the 4rd and 5th strongest El Ninos (1991-92 and 1986-87) were severe drought years at Tahoe, and 1986-87 was Mammoth’s 4th worst season ever at 5%. Nonetheless, 5 of the top 9 El Nino years (1982-83, 1992-93, 1994-95, 1997-98 and 2009-10) were at least 130% at Mammoth (orange line) and at Donner Summit (light blue line) and Lake Tahoe.
COMBINING THE AAM AND OTHER TELECONNECTIONS WITH EL NINO TO FORECAST SNOW MORE ACCURATELY FOR SKI AREAS
There are many other climatic variables that have a huge impact in snowfall around the world and the ski industry. I personally believe that global warming and climate change are having at least a “partial” adverse impact on ski resorts around the globe. For a recent interesting article in the NY Times regarding this, please click here.
Anyway, Atmospheric Angular Momentum (AAM), is just one in a series of climatic variables and teleconnections that can impact global weather and also snow totals for the ski industry. AAM is a measure of how fast the atmosphere is spinning relative to the Earth’s rotation. It is a complex variable that can offer insight to particular flow configurations within the atmosphere. Models have been showing a relative high state of AAM the last few weeks or so. During high AAM states, the atmosphere can often act like an El Nino pattern.
The higher AAM can actually help reduce the Trade Winds in the East Pacific. Hence, while no official El Nino has been announced yet this year, the atmosphere has been acting like a “ weak” El Nino State much of this winter. This could bold quite well for eastern skiing in March from Vermont to New York State, Maine and New Hampshire with snow and colder weather . The weak El Nino signal, combined with a weak +AAM has benefitted ski resorts, not only in California, but Oregon, Wyoming Utah and Colorado, as well. Many ski areas like Snowbird, Utah have had more than 100” of snow the last few weeks. This snow activity could shift to the eastern U.S. during March.
WHY THE +AAM AND ONLY WEAK EL NINO SIGNAL, EASED THE DEVELOPING DROUGHT TO N. BRAZIL SOYBEANS AND COFFEE
Let’s step away from ski weather for a moment and make an observation about the commodity markets. The positive (high) state of AAM is not in the strongest top 10% of all years, so rains have returned to key Brazil coffee and soybean areas of central and N. Brazil. In other words, a very weak El Nino signal. If there was consistently strong (not weak) +AAM from December-February, this would have jumped started the coffee and soybean markets with much more serious concerns to crops. Recently, rains have returned to key Brazil soybean and coffee regions offering a “bearish” weather spin to these markets.
My in house proprietary long range weather forecast program (CLIMATECH–below) focuses in on the positive AAM values this winter and how it predicted weeks in advance, the incessant snows out west in February and an easing of what could have been a potential serious N. Brazil drought for coffee and soybean crops.