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Cascade Snowfall and Snowdepth during El Niño and La Niña Seasons (page created December 2004, last updated April 2005) |
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See the main Cascade Snowfall and Snowdepth page for historical snowpack info. Detailed Snow Season Reports: 2005-2006, 2004-2005, 2003-2004, 2002-2003; see also Previous Seasons and Normals & Info NEW: Historical NWAC Snowdepth Data & Plots and Paradise & Crater Lake Snowfall/Snowdepth Plots |
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El Niño! The very words strike panic into the hearts of many Pacific Northwest skiers.
There is certainly a general belief, even a deep-seated fear, among Northwest skiers that El Niño seasons
are always disastrous for snowfall in the Cascades. The perception arose because El Niño tends to produce
warmer than normal temperatures in the Northwest which results in more frequent winter rainfall in the Cascades,
especially at moderate elevations such as the ski areas in the Cascade passes of Washington and Oregon. Although
this may be true, what are the real facts? Just how bad is El Niño for snowfall in the Cascades, at
elevations which are relevant for skiing? The answer was not easy to find either online via the web or offline in
printed books or journal articles, so I decided to investigate the issue in detail using the historical snowfall and
snowdepth data that I have been working with over the past few years. This is especially relevant now during the
2004-5 season, since a weak-to-moderate El Niño is underway in the Pacific. This is being blamed by many
skiers for the late opening of ski areas in Washington and Oregon and the poor early season snow conditions,
conveniently forgetting the heavy mountain snows of September-October prior to the ski season. They also forget that
the earliest Washington / Oregon ski area openings and the best early season conditions in a generation occurred
during a very similar moderate El Niño in the 1994-95 season. This page seeks to separate the facts from the
fears and the fantasy. Introduction and Definitions: El Niño is defined as "an irregularly recurring flow of unusually warm surface waters from the Pacific Ocean toward and along the western coast of South America that prevents upwelling of nutrient-rich cold deep water and that disrupts typical regional and global weather patterns." The term has entered the public consciousness and vernacular during the last two decades because the mass media has repeatedly hyped the unusual and severe weather in various parts of the globe during the past several El Niño episodes. The term La Niña has been coined to describe the opposite phenomenon, an upwelling of unusually cold water to the ocean surface in the eastern Pacific which usually has effects which are the opposite of El Niño. The entire cycle is known as El Niño / Southern Oscillation (ENSO), with El Niño forming the warm phase of the oscillation and La Niña the cold phase. The Southern Oscillation Index (SOI) refers to the barometric pressure difference between Tahiti and Darwin, Australia, which is one method used to characterize and define El Niño / La Niña episodes. A more direct characterization is the Oceanic Niño Index which is based on measured sea surface temperature (SST) anomalies in the equatorial eastern Pacific. See the following websites for general background information on both global and regional scales: |
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NOAA El Niño Page
--- ENSO Info from NOAA-CIRES Climate Diagnostics Center
--- Oregon Climate Service -
El Niño in the Pacific Northwest Climate Prediction Center - El Niño/La Niña Home and ENSO Impacts on United States --- National Climatic Data Center: El Niño Pacific Marine Environmental Laboratory El Niño Page --- IRI ENSO Information |
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An excellent readable introduction to the subject is
Currents Of Change : Impacts Of El Niño And La Niña On Climate And Society
by Michael H. Glantz (Cambridge University Press, 2001). |
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Methods of Analysis: This page discusses and analyzes El Niño / La Niña (ENSO) effects on snowfall and snowdepth throughout the Cascades. ENSO is certainly one of the dominant factors affecting the quantity and large-scale distribution of snowfall along the entire length of the Cascade Range, from southwestern British Columbia to northern California. This analysis considers only mid- and high-elevation sites, generally those above 2000 ft at the northern end of the range increasing to 5000 ft at the southern end, which are most relevant for lift-served skiing and ski mountaineering. As far as I know, this is the only analysis (online or in print) focusing specifically on ENSO effects on mountain snowfall and snowdepth throughout the entire Cascade Range. Any suggestions for improvements to this page and the ENSO analysis here would be appreciated (see my contact info). The starting point for this analysis is the chart from the Climate Prediction Center of Warm and Cold ENSO Episodes since 1950. These 3-month mean temperature anomalies are first rearranged from calendar years into snow years (July-June), and then the 8 months from August to March are summed to get a total seasonal value, referred to here as the ENSO Index. Using just the fall and winter months is better than a full 12 month sum, since these months are the most relevant for total snowfall and maximum snowdepth. Values above +7 are classified here as Strong El Niño seasons, between +3 and +7 are Weak El Niño, between -3 and +3 are Neutral, between -7 and -3 are Weak La Niña, and below -7 are Strong La Niña. These categorizations may differ slightly from those obtained using different definitions and ENSO parameters. The next step is to find measurement sites above the specified elevations which have either snowfall data or snowdepth data for a lengthy period of record, preferably the full 55 years of the ENSO index data. This is not as easy as it sounds, because there are very few such snowfall data sites, and only slightly more snowdepth (snow course) sites, which have 50+ years of useable data. Currently, a total of 16 sites with snowfall data and 34 sites with April 1 snowdepth have been selected for this analysis, including a few sites beyond the southern end of the Cascades in the Sierra Nevada to provide a cross-check of expected behavior there. The data for each of the chosen sites has been sorted into the five ENSO phase categories, averaged, and finally compared to the overall average for the full period of record at the site to determine the ENSO effects. Remember, this is a very simple analysis using only one parameter to characterize the ENSO cycle and with a fairly limited number of snowfall and snowdepth data sites. A more complicated analysis by calculating correlation coefficients between the ENSO index and snowfall/snowdepth values at these sites is beyond the current scope of this page. Results and Examples: The basic results are summarized in the table below, where the Cascade Range is divided into four distinct regions with differing ENSO correlations: 1, southwestern BC Cascades & Coast Mountains; 2, WA & northern OR Cascades; 3, southern OR Cascades; and 4, northern CA Cascades. The borders between these regions are very approximate, but lie roughly along the following areas: 1-2, south of Mount Garibaldi, BC; 2-3, south of Diamond Peak, OR; 3-4, near the OR-CA border. As expected, snowfall and snowdepth is far above normal in the Strong La Niña seasons, especially at the northern end of the range but less so to the south. For Weak La Niña seasons, correlations are less strong and the numbers are close to normal, with big snowfall years offset by several drought years. The largest category is Neutral with nearly a third of the total seasons, and on average these seasons come out slightly below normal. This may seem odd at first, but it is correct since the majority of all seasons are below average in a data set where the median is less than the mean (average), which is characteristic of snowfall and snowdepth data. The Weak El Niño seasons are generally below normal throughout the Cascades, but surprisingly they are closest to normal in BC. In Strong El Niño seasons, California typically has huge snowfalls, dropping closer to normal in southern Oregon and then well below normal in northern Oregon and Washington. Again somewhat unexpectedly, the numbers show that BC does well in these seasons, averaging near or slightly above normal at higher elevations. Low elevation sites throughout BC, WA, and OR tend to do very poorly during El Niño seasons due to the tendency for warmer than normal temperatures. |
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Regional Summary of El Niño / La Niña (ENSO) Effects on Mountain Snowfall & Snowdepth along the Cascade Range, 1950-2004 |
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| ENSO Phase | Number of Years | Southwestern BC Cascades & Coast Mtns | Washington & Northern Oregon Cascade Range | Southern Oregon Cascade Range | Northern California Cascade Range | |||||||||
| Strong El Niño | 10 | A few % above normal | 15-20% below normal | A few % above/below normal | 10-40% above normal | |||||||||
| Weak El Niño | 8 | 10-20% below normal | About 10% below normal | 10-20% below normal | 10-15% below normal | |||||||||
| Neutral | 16 | A few % below normal | About 5% below normal | About 5% below normal | A few % below normal | |||||||||
| Weak La Niña | 12 | 0-10% below normal | A few % above/below normal | A few % above/below normal | 5-10% below normal | |||||||||
| Strong La Niña | 9 | 20-30% above normal | 20-40% above normal | 15-30% above normal | 5-15% above normal | |||||||||
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A few specific examples will help to illustrate and support the broad generalizations made in the summary above. The second table shows average annual snowfall at several selected sites along the Cascade Range for each of the five ENSO phases defined above. Note that not all of these sites have snowfall data over the full 55 year period, so averages for some sites are based on a smaller number of years. Also, the summary above considers both annual snowfall and April 1 snowdepth (the snowdepth sites have higher average elevation than the snowfall sites), while the table below shows only snowfall. The sweetest number in the entire table is the stunning average of over 900" of snowfall at Paradise during the nine strong La Niña seasons, enough to put a smile on any skier's face! |
| El Niño / La Niña (ENSO) Effects on Annual Snowfall at Selected Sites along the Cascade Range, 1950-2004 | |||||||||||||||||
| BRITISH COLUMBIA | ---------------------- WASHINGTON ---------------------- | ------- OREGON ------- | ------- CALIFORNIA ------- | ||||||||||||||
| ENSO Phase | Total Years | Whistler Mtn 5450 ft |
Whistler Village 2200 ft |
Holden Village 3200 ft |
Stevens Pass 4050 ft |
Snoq. Pass 3000 ft |
Stampede Pass 3950 ft |
Paradise MRNP 5400 ft |
Longmire MRNP 2750 ft |
Govmt. Camp 4000 ft |
Crater Lake 6400 ft |
Howard Prairie 4550 ft |
Manzanita Lake 5900 ft |
Lassen Chalet 6700 ft |
Mineral LVNP 4900 ft | ||
| Strong El Niño | 10 | 426" | 146" | 227" | 408" | 333" | 363" | 615" | 107" | 202" | 468" | 123" | 203" | 515" | 160" | ||
| Weak El Niño | 8 | 343" | 96" | 217" | 454" | 426" | 452" | 650" | 164" | 280" | 510" | 139" | 204" | 396" | 162" | ||
| Neutral | 16 | 391" | 170" | 264" | 448" | 427" | 420" | 665" | 160" | 260" | 470" | 117" | 171" | 387" | 142" | ||
| Weak La Niña | 12 | 358" | 141" | 208" | 505" | 433" | 436" | 663" | 173" | 268" | 510" | 152" | 179" | 374" | 145" | ||
| Strong La Niña | 9 | 493" | 202" | 312" | 640" | 590" | 540" | 911" | 266" | 370" | 615" | 163" | 207" | 451" | 161" | ||
| Overall Average | 55 | 404" | 158" | 246" | 482" | 438" | 441" | 692" | 171" | 270" | 508" | 136" | 189" | 429" | 152" | ||
| Maximum, 1950-2004 | 673" | 274" | 409" | 967" | 828" | 705" | 1122" | 376" | 474" | 836" | 272" | 328" | 712" | 309" | |||
| Minimum, 1950-2004 | 232" | 49" | 93" | 224" | 191" | 248" | 414" | 43" | 131" | 243" | 55" | 76" | 230" | 71" | |||
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Conclusions: An important conclusion from all of this data is to largely refute the common misconception among Pacific Northwest skiers that El Niño seasons are always terrible for snowfall in the Cascades. El Niño certainly does produce warmer than normal temperatures in the Northwest. However, El Niño seasons typically do have adequate precipitation, resulting in winter rainfall but also adequate snowfall, especially at higher elevations which are most important for spring/summer skiing and ski mountaineering. The strong El Niño average snowfalls of 330-400" at the major WA Cascade Passes and 600" at Paradise are certainly not bad at all, most other regions of the country only dream of such snowfall amounts. And the southern end of the Cascade Range does very well during El Niño seasons, with spring snowdepths averaging 20% above normal on Lassen and nearly 40% above normal on Shasta. The very worst snowfall seasons in the Cascade range, the real disasters, occur during severe drought years which are not well correlated with El Niño. The five worst Cascade snow seasons overall since 1950 have been 1962-63, 1976-77, 1980-81, 1991-92, and 2000-2001, of which only one is strong El Niño, one is weak El Niño, one is neutral, and two are weak La Niña. El Niño seasons are rarely disastrous for snowfall in the Cascades, but they are usually somewhat below normal in Washington and Oregon while averaging slightly above normal at higher elevations in British Columbia and much above normal in California. The correlation between ENSO and snowfall is much stronger in the opposite La Niña phase, and strong La Niña seasons are almost always above normal throughout the entire Cascade Range, especially so in the northern two-thirds of the range. The record-high snowfall and snowdepth amounts at most locations in the Cascades of Oregon, Washington, and British Columbia were set during strong La Niña seasons, while in the California Cascades they were set during strong El Niño seasons. The graphic below shows the spreadsheet containing the full data analysis on which the results and conclusions on this page are based. The spreadsheet itself is not very illuminating, but perhaps some readers may be interested in looking at the raw numbers and the guts of the analysis. Click the image to view a full-size readable version. |
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Data used for the analysis on this page provided by:
NOAA Climate Prediction Center, Western Regional Climate Center, National Climatic Data Center, Environment Canada National Climate Archive, Oregon & Washington Snow Surveys (NRCS), California Cooperative Snow Surveys, British Columbia River Forecast Centre, Whistler Blackcomb Ski Resort, Mount Rainier, Crater Lake, and Lassen Volcanic National Parks. |
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