Seasonal reading—that’s my boring-but-apt term for enriching the mood and meaning of a certain time of year with the addition of a certain text. Each April, I reach for the “Spring” chapter in Walden. Every July, I take a lap in E.B. White’s “Once More to the Lake.” And in November, when the brown ground freezes and the weatherman predicts five months of blizzard, I cozy up on the couch with a mug of chamomile tea and “The Ascending Spiral,” a short, dense essay by the legendary snow scientist Ed LaChappelle.

　　Lynne Wolfe, editor of The Avalanche Review, which published “The Ascending Spiral” in 2005, calls the essay a seminal work. I got turned on to it a decade ago by my friend Jerry Roberts, a retired avalanche forecaster for the Colorado Department of Transportation and self-described “snow-viewer.” (Seventeenth-century haiku poet Matsuo Basho: “Come, let’s go / snow-viewing / till we’re buried.”) Roberts and LaChappelle were colleagues and pals. They worked together in the San Juan Mountains in the 1970s and shared a bottle of pisco a mere week before LaChapelle suffered a fatal heart attack at Monarch Pass—skiing, of course—in 2007. “Required reading,” I was told.

　　LaChappelle frames his essay as a contribution to the never-ending discussion among snow-viewers, both professionals and hobbyists, regarding how best to “evaluate avalanche hazards, consider human factors, and communicate (or execute) decisions.” There is much practical wisdom in these pages, actionable advice for telemarkers, splitboarders, snowmachiners, alpinists, and gonzo backcountry tobogganists. But the really special thing—the reason I’m drawn to “The Ascending Spiral” each November—is the brief and tantalizing treatment of rheology and the Deborah Number.

　　The what and the what?

　　My initial reaction, too.

　　Rheology is a branch of physics that deals with the deformation and fluidity of matter. For instance, gummy bears—pop a few in the microwave and behold the freaky carnage. Snow is another fine example, defined by LaChappelle as “a granular visco-elastic solid close to its melting point” that subtly, constantly, and complicatedly responds to its environment, fluctuations in temperature and pressure in particular. He asks us to envision a peak in winter. “From the external perspective of a passing observer, snow on a mountainside is just sitting there, apparently dormant. The snow cover, however, is neither static nor dormant, but a positively seething mass of activity.” Learning to see it as such—to see it as dynamic, as lively and perhaps even alive—is the challenge and the fun.

　　Enter the Deborah Number. Proposed in 1964 by the pioneering rheologist Markus Reiner, the concept (it does not refer to a specific, fixed number) takes its name from a Biblical prophetess who sang of the mountains “flowing before the Lord.” LaChappelle sums it up like this: “In the limited time frame of human perception, the mountains are static and eternal, but for the Lord, whose time frame is infinite, they flow.”

　　LaChappelle was a Professor of Geophysics and Atmospheric Sciences at the University of Washington and a co-inventor of the modern avalanche transceiver, whereas I flunked Algebra 2, confounded by the damn TI-82 graphing calculator. Nevertheless, this stuff greatly excites me. Per my layman’s understanding, the Deborah Number is an expression of the relationship between time spent observing natural phenomena and perception of flow—high D equals scant time and we don’t see the flow, low D equals tons of time and we do see the flow. A hastily dug snowpit on an unfamiliar slope (high D) yields “a static view of what actually is an active (‘flowing’) snow cover.” LaChappelle continues: “In other words, stability evaluation has to be an ongoing process, the longer the better.” Ideally, it starts on a given avalanche path with the first flakes of winter.

　　Meticulous and relentless monitoring of this sort is the hallmark of an avalanche forecaster’s job. As Jerry Roberts told me in 2016, during an interview I conducted for the Buddhist magazine Tricycle about the Zen-like aspects of patrolling (meditating on?) the sketchy San Juans and their avalanche-prone high-mountain passes: “You’re afraid to go shopping at the supermarket an hour away because you might miss a wind event. You can’t be absent from your place. You have to be totally present.” I recall him chuckling, shaking his head, seemingly amazed by the stamina and focus of his younger self. “You don’t think about Christmas or your wife’s birthday. You don’t go on vacation. A series of storms in ’05 lasted ten days. I got very little sleep.” Chuckle, shake. “From November through May, paying attention is what you do. It’s who you are. There’s no difference between on and off.”

　　Indeed, for the snow-viewer whose entire existence is devoted to detecting and registering slow-motion transformations occurring at both micro and macro scales, whose sacred daily mantra is lower the D, lower the D, lower the D, lower the D, the on-versus-off question is moot. Case in point: After a career in the field researching glaciers, LaChappelle retired to a remote cabin in McCarthy, Alaska and busied himself tracking—surprise, surprise—the nuanced behavior of his local glaciers.

　　I’m sporadic and undisciplined when it comes to studying the ever-shifting details and ever-morphing character of Colorado’s Elk Mountains, my home range. Hence my need to sit with “The Ascending Spiral” each November as the thermometer’s mercury plunges and the touring gear beckons from my mudroom’s cobwebby corner. I skin up and float down a couple mildly dangerous peaks most winters—beacon, shovel, probe, goofy buddies, and lots of laughs—so in part I read to humble myself: Pay attention, boy, or else! According to the Colorado Avalanche Information Center, one hundred and forty-nine people got caught in slides last ski season and, sadly, two didn’t survive. The or else is exceedingly real.

　　Ultimately, my enthusiasm for rheology and the Deborah Number is less utilitarian—a means to the end of protecting my vulnerable ass while poorly carving powder 8s—than it is aesthetic and spiritual. I like to poke around the valley floor and gaze at the intricacies of the snowscape. I like to sculpt a drift into a chair, crack a beer, and stare. I like to approach perception as a kind of basic yet mysterious adventure. I like to notice, and notice that I’m noticing, and keep on noticing, and keep on keeping on. So in part I read to be humbled, yes, and in part—in large part—I read to be inspired, encouraged, nudged toward a cool way of inhabiting my place: Pay attention, boy, because lowering your D is a worthy end in itself! An awesome pastime! A beautiful and demanding practice! A raison dêtre!

　　Do I aspire to godliness, an omniscient and infinite vantage? Nah, too grand for my earthly tastes. But looking through those eyes now and then, on occasion, is a huge thrill. Stealing a glimpse of the perpetually changing, fleeting, flowing planet. Feeling that glimpse, at my luckiest moments, as an electric tingle racing the length of my spine.

　　I felt the tingle recently, following my annual twenty-minute check-in with dear old Professor LaChappelle on the couch. Five or six inches of snow had fallen in the high country the evening prior and I suspected that, unlike the flurries of early autumn, which disappeared quickly from the summits, this coating of white would stick. Or maybe I hoped it would stick, eager for the schuss, the glide, the burn, and the turn.

　　The essay finished, at least until next year, I drained the dregs of my tea, stepped into the yard at sunset, lifted my binoculars, and scanned the wilderness of ridges and faces and bowls that rises abruptly to the west of town. Conditioned by my quasi-ritualistic re-reading of “The Ascending Spiral,” what I saw had the quality of epiphany. It was “a granular visco-elastic solid close to its melting point.” It was gummy bears in the microwave, a quintillion protean crystals. It was the foundational layer of a new winter’s breathing, pulsing, growling, tail-whipping snowpack—a snowpack guaranteed to spawn the avalanches that Jerry Roberts and other animistic snow-viewers call “dragons.” It was simple and complex, common and strange, mundane and magical.

　　I pocketed the binos, zoomed out.

　　What I saw was a paradox, tingle-inducing for sure—the whole world perfectly still, not a bird, not a cloud, not a hint of a breeze, not a single trembling blade of grass, and there on the horizon, washed pink with alpenglow, something deep inside the stillness beginning, secretly, to move.