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Tutorial: How to predict backcountry weather conditions || Methods & sources for short & long trips

Lost Tribe Lakes in Colorado’s Indian Peaks Wilderness after a violent afternoon monsoon storm

I have said this before, and continue stand by it: there is a right way to backpack: equip yourself with the gear, supplies, and skills that are appropriate for the conditions and your trip objective.

Among the conditions that I consider (there are about 10; view the full list), the weather — specifically temperatures, precipitation, humidity, and wind — has an outsized role on my preparations, because it:

  • Affects several major systems, including my clothing, shelter, and sleep; and,
  • Undergoes monthly, weekly, daily, and sometimes hourly variations.

By comparison, other environmental and route conditions have a narrower impact and/or are more predictable. For example, the presence of problem bears affects only one item — my method of food protection; and throughout the summer I expect heavy tree cover on the Appalachian Trail, and intense sun exposure above treeline in the Rockies and High Sierra.

How do I familiarize myself with the weather conditions that I will likely encounter on a backcountry trip? In this post I’ll share my methods and sources.

Challenges

It’s easy to find the weather forecast, seasonal averages, and daily records for population centers. The information is available from multiple sources, including the National Weather Service, The Weather Channel, and local news stations.

Accurate data for backcountry locations is more scarce, because:

  • Fewer weather stations have been installed in remote locations; and,
  • Mountains make their own weather, causing conditions to vary significantly with elevation and geography.

For example, it’s considerably warmer and drier in the town of Nederland, Colo., than atop Arapaho Peak, which is just 8 miles to the west-northwest but 5,000 vertical feet higher and atop the Continental Divide, which catches storms that push west through Colorado. Nederland is also drier than Winter Park, which sits at a similar elevation but which is on the wetter west side of the Divide.

Weather that matters

When I look at weather data, I’m interested mostly in temperature and precipitation. More specifically:

  • Temperatures: Average high and low, and extreme highs and lows; and,
  • Precipitation: Frequency, amounts, and patterns.

Humidity and wind are also important, but it’s more difficult to find this data outside of a short-term forecast. So I run with some assumptions:

  • Locations east of the 100th Meridian and coastal areas in the Pacific Northwest and Alaska are humid.
  • Locations west of the 100th Meridian are dry, except when storms roll off the Pacific (mostly between November and April).
  • The plains are the windiest region in the country. Ridgetops and peaks are wind-prone, too, especially when storms are passing through or when weather systems are changing.
  • If I can find a protected campsite (among natural wind breaks like trees or canyon walls), wind is usually not a significant factor at night.

Considerations for trip length

For shorter trips, I base my planning around weather averages and normal extremes, and then tweak my selections last-minute based on an actual forecast. Conditions are most likely to be average, but I need to be prepared for abnormal weather, too.

On longer trips, I expect average conditions overall, but more extremes. For example, on a three-month thru-hike, I might experience 8 weeks of average conditions, two weeks of abnormally wet and cold conditions, and two weeks of abnormally warm and dry conditions. Overall, the conditions were average, but I saw more variability than I would have on a shorter trip.

How do I define trip length? A “short” trip is anything less than about 5 days, which is the normal outer limit of my trust in weather forecasts. Between 5 and 10 days, forecasts can be suggestive (e.g. a storm front will arrive in about a week) but I take them with a grain of salt. A “long” trip is anything beyond 10 days, when the weather becomes anybody’s guess.

Short-term planning

The night before I depart for the backcountry (and sometimes even the morning of) I always get a weather forecast. Knowing the weather will not change the weather, but it may change my decisions, like where I camp and the boldness of my route.

My preferred source of information is the National Weather Service. Yes, I still believe in our institutions.

The forecast for the town closest to my route will not necessarily be relevant, so instead I get a “point forecast” by clicking on a more specific location on the embedded map. Depending on the route, I may grab several forecasts, like for high and low points, and for opposite sides of a weather-making divide.

As of the afternoon of June 1, here’s the forecast for Grand Lake, Colo, the gateway town to Rocky Mountain National Park on the west side:

But along the Continental Divide Loop at 12,000 feet, where I’d rather be hiking, the forecast is more severe. The daytime highs will be 15 degrees cooler, and this weekend there is a higher chance of rain and even snow:

To better understand the timing and severity of inclement weather, I may look at the Hourly Weather Forecast, listed under “Additional Resources.” I find this graph to be more useful than vague descriptions like “chance of rain showers, mixing with snow after 9 pm.” I sometimes will also read the Forecast Discussion, which gives more color and macro context to the data.

In addition to NWS, several other resources are worth mentioning. Some are relevant only for particular seasons or locations.

Long-term planning

My experience is that short-term forecasts are not always spot on, but that they’re usually accurate enough to assemble a proper kit and to set trip expectations. For example, the forecast may underestimate the amount of rainfall, but it was still predicting rain, and so I would have taken my rain gear and an appropriate shelter.

But normally I can’t wait until the last-minute to gear up. For example, if I plan to leave after work on Friday, I’ll want to pack earlier in the week. And if I were thru-hiking the Pacific Crest Trail, I couldn’t wait until the day before to purchase my gear, especially since some cottage companies have wait times of several months.

Where exactly do I find seasonal averages?

National Center for Environmental Information (NCEI)

For most of the country, I start with the National Centers for Environmental Information (NCEI), a division of the National Oceanic And Atmospheric Administration (NOAA). More specifically, I dig into the monthly climate normals for its COOP stations from 1981 to 2010, using its:

The intuitiveness of both tools needs improvement, but they’re generally an improvement over what was provided by the Regional Climate Centers before the information was consolidated under NCEI a few years ago. For example, the Western Regional Climate Center’s search tool had not been fundamentally updated since the early-2000’s.

To retrieve the desired data from NCEI, you may have to play around with its tools for a while. Hint: Find a relevant COOP station, add the data to your cart, and “checkout.” It’s free, and you’ll receive an email with a download link. The CSV or PDF file will contain data like this:

SNOTEL

The Natural Resources Conservation Service (NRCS), a division of the Department of Agriculture, operates over 800 automated data collection sites, primarily in the western US and Alaska. Data from the Snow Telemetry (SNOTEL) Network is used for water supply forecasting, maps, and reports.

To find SNOTEL sites, use CalTopo and turn on the “SnoTel Sites” layer. Then find one (or a few) close to your route.

SNOTEL stations record and monitor temperature, precipitation, and snowpack. To retrieve temperature and precipitation data, I like to use its Report Generator 2.0.

California

The state of California has its own monitoring system for weather, snowpack, and river and reservoir levels, managed by the Department of Water Resources. Some states may have a similar program, but I think it’s probably unique — it’s expensive to install and operate. Start with the station locator map, and work with the tools provided to get useful data.

Data adjustments

Temperature and precipitation normals that are retrieved from NCEI, SNOTEL, and California are station-specific. If these stations are close but not on your route, adjust the data to make it more relevant.

Temperature. For every 1,000 vertical feet of elevation change, adjust 3 to 5 degrees F — 3 degrees for humid climates, 4 degrees for semi-arid, and 5 degrees for arid.

Precipitation. Rainfall and especially snowfall increase exponentially with changes in elevation and geography. Locations that are higher and that are on the “wet” side of a major divide will receive significantly more rainfall and snowfall than lower locations in the rainshadow of that divide.

Questions about my methods and sources? Do you rely on different ones? Leave a comment.

14 Responses to Tutorial: How to predict backcountry weather conditions || Methods & sources for short & long trips

  1. Dave Nelsen June 4, 2018 at 7:31 am #

    Great resources, thanks Andrew! Particularly when the forecast is unsettled and I am out with my Scouts or Venturers, I will usually pack along my Midland HH50B pocket weather radio – smallest one available. I double-check radio coverage through the NOAA website http://www.nws.noaa.gov/nwr/coverage/county_coverage.html

    • Andrew Skurka June 4, 2018 at 8:19 am #

      Having access to real-time weather in the field is a good idea with unsettled weather. I didn’t mention in-the-field options in the post, but there are a few. Personally, I use my inReach, since normally it goes with me on longer trips.

  2. Axel June 4, 2018 at 8:15 am #

    I agree with you on the NWS, they have a wealth of information and tools. I use this map to see real time conditions in the Sierra where they actually have quite a few remote monitoring sites:

    https://www.wrh.noaa.gov/map/?obs=true&wfo=vef&basemap=OpenStreetMap&boundaries=true,false&obs_popup=true

    Another source is the US Navy public facing portal FNMOC, especially the 6 hour precipitation maps and long range ensembles to see how weather trends are developing and evolving:

    http://www.metoc.navy.mil/fnmoc/fnmoc.html

  3. JP June 4, 2018 at 9:21 am #

    I also like https://weatherspark.com/ which provides excellent graphical representations of climate variables. They integrate data from weather stations and other government sources.

  4. Justin June 5, 2018 at 8:48 am #

    A bit tangential to this post, but is there a resource for estimating bug pressure when you plan a trip?
    I’ve had a hard time figuring out when a bug net, repellent, etc might or might not be advisable, so I often pack the weight only to discover it wasn’t really needed.

    • Andrew Skurka June 5, 2018 at 11:40 am #

      Not that I know of. Best resources will be trip reports, rangers, and guidebooks.

  5. Matt Jacobs June 5, 2018 at 10:28 am #

    Andrew, I don’t want to be spamming your blog, but I’m curious if you’ve used CalTopo’s “weather forecast” layers? Interpolating between multiple NOAA point forecasts is exactly why I built them. There’s a surprising amount of small-scale variability in the 2.5km forecast grid, and sometimes clicking one grid square over on their point forecast tool can significantly change the forecasted wind, temperature or snowfall – but it’s hard to determine that using their site without a lot of trial and error.

    • Andrew Skurka June 5, 2018 at 11:40 am #

      Your comments are always welcome here.

      No, I had not used those layers. In fact, I didn’t even know they existed.

      I just played around with it for a few minutes. Is the following statement correct? “Though CalTopo you can access up to 48 hours of point-forecast weather data (high and low temps, rain & snow, wind).” This would make it another “short-term planning” resource, but not something that is useful months out, right?

      • Matt Jacobs June 5, 2018 at 12:39 pm #

        That’s correct, it’s short-term only.

  6. Joe June 5, 2018 at 1:08 pm #

    From the perspective of an old man, whose first significant winter wilderness trip in Colorado was a projected 5 day ski traverse of the CD in ’73, but ended after 4 days of blizzards, yet to reach the Divide, with my partner experiencing acute appendicitis, (he survived, but barely), I find this stuff sad, if not troubling.

    You go prepared, and you deal with what you get.

    Again, I’m old. It was another country then.

  7. Joe June 5, 2018 at 2:08 pm #

    I wonder though. Will there come a time when the adventure, the challenge of your “adventure”, ceases to satisfy, as you know what to expect?

    Prolly not. You got her done, just as planned.

    It seems to me that the wealth of information available might be detrimentally affecting the value, even the adventure of the wilderness experience, for those who seek to maximize it.

    • Andrew Skurka June 5, 2018 at 3:45 pm #

      You’re not looking at it the right way. By knowing more before I go, I’m able to undertake much more ambitious projects than those who didn’t have access to the same info.

  8. Lyle male Gordon June 5, 2018 at 11:28 pm #

    I wasn’t aware of the California Department of Water Resources weather stations. I had seen a station up at Highland Lakes but never knew who ran it or how to find the information. Thanks for this great resource, some of the areas are missing SnoTels.

  9. Travis Briles June 14, 2018 at 8:20 am #

    Hi Andrew-

    I really enjoyed this post. Thanks! I think a companion post about evaluating weather conditions “on the fly” would be useful. For isolated day-trips in the mountains, one usually has the ability to pick a perfect weather window. For longer trips you will inevitably get “some” bad weather.

    For concreteness, consider this “hypothetical” scenario which I imagine many readers of your blog could themselves in. You have a 6-8 day trip in the mountains above treeline that has fairly rigid start and endpoints. Your weather window looks basically good but days 4+5 are predicted to have a 50% chance of thunderstorms. If every day was predicted to have bad storms you’d reschedule, but you decide to go for it. The plan for days 4 and 5 is to get a start at 4AM and be over peaks, passes etc by noon. On day 2, you’re well above tree line and the bluebird skies transition to clouds, then thick clouds, then light rain. You don’t remember thick clouds/light rain being in the forecast on day 2 but can’t remember and you forgot the printout in the car.

    Are there high probability indicators (cloud type? specific pressure drop? rate of onset? extent of cloud coverage?) that the changing weather will evolve into something serious? If it was just going to be light rain, I think many people would just power through it but would obviously avoid peaks/ridgelines in a lightning storm.

    Also, I’ve been wondering if Colorado mountain weather is in general more unpredictable than other mountain areas (Sierra’s, Wind River Range, Cascades, Absaroka’s etc)? I heard this recently but didn’t know if the claim was basically the Colorado equivalent of “everything is bigger in Texas”.

    I realize these questions may be very hard to answer but any insight would be appreciated.

    Thanks!
    -Travis

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