Debris from wet, loose avalanches in the Pika Glacier, Alaska in June 2014. Photo: Spencer James

Debris from wet, loose avalanches in the Pika Glacier, Alaska in June 2014. Photo: Spencer James


The Inertia

Thousands of skiers around the country are gearing up for their local mountain’s opening day. Some have already set out to rip their first blissful turns in Colorado, Utah, and a number of other states with resorts sporting earlier starts. For others who slap skins on their skis and packs on their backs, only the local weather forecasts constrain their seasons. But how do you decide when the time is right? Which early-season storm warrants dusting off your avy gear and venturing out onto some barely covered meadows? And once the middle of the season rolls around, how do you pick a day and location that satisfies both the hunger for face shots and the need for self-preservation? It all starts with weather forecasts, and in today’s information age it’s pretty easy to find more weather predictions than you could possibly look at.

As a former ski racer turned ski mountaineer, I spend a lot of time each winter paying attention to the weather. For the past couple of years, I have patrolled for Cascade Backcountry Ski Patrol (CBSP), a volunteer ski patrol covering regions of the Washington Cascades, while responding to winter backcountry accidents as a member of the King County Ski Patrol Rescue Team (SPART). After moving to Berkeley this summer to start a graduate school program, I’m planning to spend this winter exploring the Sierras and continuing to patrol through the Tahoe Backcountry Ski Patrol (TBSP). All of this lends to a rather extensive studying of forecasts, and with that in mind, I’d like to share a handful of the lessons I’ve learned through my own personal experiences.

No resort closing dates constrain skiing opportunities in the Alaska Range. Photo: Spencer James

No resort closing dates constrain skiing opportunities in the Alaska Range. Photo: Spencer James

So here are three quick tips to keep in mind to glean some useful information from forecasts and avoid being overwhelmed by an avalanche of data:

Check out at least one local and one regional forecast.

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My first stop for weather data is typically a National Weather Service (NWS) point forecast. The NWS operates the sensing equipment that feeds most weather models in the U.S. Forecasters use these models to come up with the predictions you see when you open your web browser or change the channel to your local news station. Don’t let the “point forecast” name fool you, however; these predictions are based on regional forecasts (see “Current Conditions at” near the top of the linked page) that are then interpolated to the point you have selected.

Typical point forecast from the National Weather Service. Image: National Weather Service

Typical point forecast from the National Weather Service. Image: National Weather Service

Regional forecasts like those provided by the NWS provide a systematic forecast method that you can compare across regions and over time, but they oven don’t take into account local topography. If you happen to know that a particular valley you are headed to is a well-known wind tunnel, or a certain area experiences higher precipitation than its surroundings, then a local forecast might give you more accurate information. At the same time, these forecasts often aren’t depicted in the same data-rich, easy-to-skim format provided by the NWS, and you can’t interpolate to your exact destination. What’s the solution? Well, reading both types is a good place to start. If they agree, then you know what the weather will look like with reasonable confidence. If not, you might want to keep investigating. This brings me to my next point…

Pay attention to uncertainty.

When using weather to plan ski trips or mountaineering objectives, you should consider both the predicted values and the uncertainty associated with those predictions. A general rule of thumb is that weather forecasts for the next week are useful for generating tentative plans, while three-day predictions can often be used when firming up plans. More than one week out, you can’t get much more information out of forecasts than you can looking at historical averages. But rules are made to be broken, and this one is no exception. Storm systems can be predictable or unruly. They may gain strength as they cross an ocean, or they may shift directions suddenly. Human nature is to seek the simplest understanding of a system, so we are drawn to mean estimates more than uncertainty. This is a problem when planning your next outing, but the question remains: how do you get a feel for the uncertainty associated with a forecast? It’s not always easy to understand from checking out a single forecast, since their outward-facing predictions usually identify only the “expected” temperatures or precipitation amounts. You could really dig in and look at all of the numerical models that forecasters rely on to come up with these models, but the majority of us would be lost without a degree in meteorology.

Screenshot of an animated temperature, humidity, and wind model. Image: Air Resources Library

Screenshot of an animated temperature, humidity, and wind model. Image: Air Resources Library

My simple solution is to pick a couple of sources and compare them. This could be one local and one interpolated regional forecast (see tip #1), or they could be two regional forecasts. Most available forecasts (NWS, mountain-forecast.com, The Weather Channel, etc.) are based on subsets of the same group of predictive models. If all the forecasters and algorithms employed by these various organizations are looking at the set of models and coming up with the same conclusion, then you can probably bet that their predictions will somewhat accurate. If they give you wildly different numbers, you might be rolling the dice trying to plan your trip around the weather. Another good rule of thumb is to prepare for the “worst case weather,” whatever that means for your plans. The more uncertainty expected in a forecast, the greater the margin of error you need to prepare for. In other words, if your go-to weather site is predicting 30 degrees and 6 inches of snow, while another forecast says 33 degrees and rain, you should prepare for rain. This goes for avalanche safety, too. The less certainty you have in assessing the avalanche problem, the more you should assume the worst.

Look at trends in addition to point estimates.

I can’t tell you the number of times I’ve checked a weather forecast, seen some pleasant mild weather, and arrived at the mountains to find an inch of light snow on top of a miserable rain crust. If you haven’t yet skied in the Pacific Northwest, you might have to trust me that this can be more the norm than an unfortunate exception. Even on a big expedition to the Alaska Range this summer, I was seduced by talk of several meters of snow in the past couple of weeks. When we arrived, we understood just how much of an impact a recent warming trend had had. As we hunkered down in camp and listened to wet, loose avalanches tumbling down all of the beautiful couloirs we had seen from the air, we cursed the recent snow more than praised it.

Often, findings like these wouldn’t have been as surprising if I’d taken the time to look at past temperature and precipitation trends. Too often we’re drawn to the predicted weather (“Dude, there’s gonna be six inches tonight! Let’s head up tomorrow!”) and don’t pay attention to what’s already happened. Weather telemetry (data collected via automated, remote sensing equipment) is especially valuable because there’s no uncertainty. We know what the weather was yesterday because it already happened. For this reason, make sure you take a look at telemetry whenever you look at predictions. This can be particularly important when venturing into avalanche terrain (which is, of course, almost any backcountry ski destination worth your time). Weather and precipitation trends can often tell you whether you have a “rightside-up” or “upside-down” snowpack, which has a significant bearing on stability of potential storm slabs. (Note that this, of course, is not the only factor affecting stability so make sure take an avalanche safety class if you haven’t yet. There’s absolutely no substitute for a formalized education.)

Understanding weather forecast nuances may help you avoid some uncomfortable days, but they may also save your life. I’ve mentioned but a few of the numerous aspects of weather that you can consider when planning your next outing, and I encourage you to explore forecasts further. In addition, the tricks I mentioned are just the ones that others have shown me over the years and that have come in handy when planning my own ski tours. If anyone has some advice to add, please do so in the comments section! And stay tuned for the next installment in this weather series, which will discuss unique aspects of weather in different regions.

Stay safe out there!

Photo: Spencer James

Photo: Spencer James



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