High hopes for a ‘Drought Buster’
The Sierra Storm King kicked it up a notch in October, dumping 50 inches of snow at the Central Sierra Snow Laboratory (CSSL) located near Donner Pass. The impressive snowfall total is the greatest amount on record since the CSSL was established in 1945, and a solid 500 percent more than the average October snowfall total of about 9.5 inches. Cold storms barreling in from the Gulf of Alaska generated the early season precipitation. Locally, the exceptional weather fired up the winter sports industry and gave residents worried about drought and fire potential something to smile about. The heavy rain and snow set precipitation records throughout California and doused the medley of raging wildfires plaguing tinder dry forests and rangeland. The storms effectively shut down a volatile and destructive fire season.In Sacramento, more than 3 inches of rain, about 300 percent of normal, placed it as the fifth wettest October on record, but the real precipitation anomalies are to be found in Southern California. October rainfall totals in the southland ranged from about 4 to 6 inches; Los Angeles picked up 1,050 percent of normal, Riverside almost 1,500 percent, and in Santa Ana, the 6.07 inches measured there is nearly 1,700 percent of the October average. But these exceptional deviations from normal don’t tell the whole story. When meteorologists consider the likelihood of a weather event repeating itself in any given location, they use a mathematical formula to calculate the Return Period (RP), which is often measured in years. According to data provided by Jan Null, a certified consulting meteorologist in San Francisco, the RP for the 3.09 inches recorded in Sacramento this October is about 25 years. In San Diego, the RP for the 4.53 inches measured there is 3,000 years, in Santa Ana, 9,000 years, and in Long Beach, an incredible 10,000 years! Keep in mind that a 10,000 year Return Period does not mean that you have to wait 10,000 years for another event of the same magnitude. It means that there is a one in 10,000 probability of a similar precipitation event happening at that location in any given year.
Let’s not get ahead of ourselvesEnjoy the skiing and boarding before Halloween and Thanksgiving because it’s a real treat, but don’t start feeling overconfident about this year’s snow season. People should remember the winter of 2000-01, which exhibited similar early season precipitation patterns to this year. Both years boasted September snowfalls of 3 to 5 inches, and both years were treated to unusually cold and snowy, winter-like storms in October with early resort openings. Unfortunately, 2000-01 fizzled and ended drier than normal, with many Sierra resorts closing earlier than usual due to marginal conditions and lack of interest.Winter sports enthusiasts, hydrologists, and everyone who appreciates a healthy ecosystem, are all hoping that the winter of 2004-05 brings plenty of snow and rain to replenish our desiccated watershed. It will be a first step in breaking a tenacious five-year drought in the region. Using climatology to predict weather is often a dubious endeavor, but the recent precipitation may be a good omen. Out of the top 20 wettest Octobers on record in San Francisco (October 2004 ranks 17th), 11 seasons ended near normal, six were above average, with only three drier than normal. These data suggest that an early start in October generally trends towards a normal or above average water year in Northern California, and as November gets under way with more snow falling, there is reason to be optimistic.
On the other hand, there is a weak ENSO (El Niño Southern Oscillation) simmering in the Pacific Ocean. Generally, strong ENSO events increase the chances for a wet winter in the Tahoe-Truckee area, but because this year’s El Niño conditions developed late, and ongoing measurements of sea surface temperatures suggest little strengthening, scientists are forecasting a weak to moderate event. Edward O’Lenic, chief of climate operations for the National Oceanic & Atmospheric Administration, reports that in the last 40 years, there have been five winter seasons with El Niño characteristics similar to this one. During those years – 1963-64, 1969-70, 1976-77, 1977-78, and 1987-88 – Donner Pass only exceeded its average seasonal precipitation in 1969-70 and 1977-78. More worrisome, the winter of 1976-77 is one of the driest on record at the Central Sierra Snow Lab. Indicative of the cyclic nature of our western climate, where extended droughts are often broken by heavy winter weather events, it was only a decade ago that Lake Tahoe’s water level had fallen to 6,221.20, nearly two feet below the natural rim. In November, hydrologists were estimating that it would take ten years to refill Tahoe. A six-year drought had taken its toll and everyone was praying for a big winter, a real “drought buster.” A quick snapshot into the roller-coaster winter of 1994-95 reveals that residents got an early dose of wintry weather when vigorous storms invaded in November. Records for cold and snow were broken throughout northern Nevada and California. December, however, brought a lull in the rampage and proved to be one of the driest ever in the region. Just when folks were getting worried, in January the Storm King pummeled the Sierra with heavy precipitation; Truckee exceeded 200 percent of normal while Tahoe City was drenched with more than 16 inches of precipitation (rain and snowmelt), about 270 percent of average. In contrast, February was the warmest in Reno since records began in 1888 and precipitation in the Sierra only 24 percent of average. But March came in like a lion and incessant storms hammered the region. Precipitation values soared to 335 percent of average throughout the northern Sierra Nevada and set the stage for near record runoff. More wet weather in April forced hydrologists to revise their water runoff projections upward once again.
The moderate El Niño event that year may have contributed to the vigorous storm pattern. Alpine Meadows Ski Area was blessed with 662 inches of snow, the greatest on record for that location. More important to the region’s hydrology, the Central Sierra Snow Laboratory measured 52 feet of snow containing 105 inches of water. This is nearly nine feet of water and only seven inches shy of the all-time record set in 1981-82. On May 2, 1995, snow surveyors measured 125.6 inches of water in the snowpack at Squaw Valley’s Gold Coast survey site, which represents 10 and a half feet of standing water. Lake Tahoe rose dramatically in 1995, from more than two feet below the rim, to a discharge into the Truckee River stream flow estimated at 240 percent above normal. Keep the faith and hope for a drought buster. We’re due.Mark McLaughlin’s column, “Weather Window,” appears monthly in the Sierra Sun. His award-winning books, “Western Train Adventures: The Good, the Bad & the Ugly” and “Sierra Stories: Trues Tales of Tahoe, Vol. 1 & 2” are available at local bookstores. Mark, a Carnelian Bay resident, can be reached at email@example.com.
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