Getting Started with Snowshoe Routing in the Washington Cascades
I've been building route plans for backcountry snow travel in Washington for about a decade now, mostly around the Cascades. Dan A Nelson put together some solid Snowshoe Routes Washington Dan A Nelson documentation and datasets that are genuinely useful if you know how to work with them properly. Most people I see online either give up after thirty minutes because the format doesn't look intuitive, or they import it blind and walk into trouble because they don't understand the projection assumptions built into the source data. At its core, the Nelson snowshoe routes dataset is a collection of GPS-tracked winter travel corridors across the western slope of the Cascade Range. The data was compiled from field expeditions over roughly four years and covers terrain from the Skykomish Valley up toward the Entiat River corridor. It exists primarily in ESRI shapefile format with accompanying attribute tables that track trail difficulty ratings, elevation gain segments, snowpack reliability notes, and seasonal closures. The original files include WGS84 coordinates but also carry an embedded NAD83 HARN reference in the prj file that trips up anyone running a quick import through basic GIS software. I spent two hours last January debugging a route that looked perfectly fine until the waypoints were off by about forty meters because QGIS defaulted to the wrong datum transformation. The fix is straightforward — force the on-the-fly reprojection to use NAD83 to WGS84 using the NTv1 grid shift rather than the default seven-parameter Helmert approximation. It saves you from showing up at a trailhead that doesn't exist on the ground.
Setting Up the Data for Practical Use
Download the files from the repository, which still hosts the original zip package. Don't unzip everything into one folder with the rest of your GIS projects. The attribute tables reference external CSV files using relative paths that break if you move anything around. I keep a dedicated workspace for this dataset and symlink the raw files so the internal references stay intact. Once you open the shapefile in any standard GIS application, you'll notice the attribute table has a field called ROUTE_CLAS that maps to a coded value table. The values run from 1 through 5, where 1 is packed-snow travel corridor with minimal obstacle clearance and 5 indicates unmarked cross-country routes requiring route-finding skill. This classification is based on winter conditions as they existed at the time of the survey, so treat any rating 3 or above as a best-case scenario. Deep powder years or warm winters can shift a route 2 classification into something closer to 4 in practice. The elevation gain field, ELV_GAIN_FT, only captures cumulative ascent between waypoints. It doesn't account for the undulation between points. If a route shows 1,200 feet of gain but you're actually traversing several ridgeline sections with local highs and lows you won't see in the summary, the real effort is higher. I've learned to add roughly fifteen percent to whatever that field reports when planning turnaround times.
Working Through a Real Route
Take the route labeled SK-047, which runs from the Lake Vallee access area toward the Stevens Pass snowshed zone. On paper, it's rated 2, about 3.8 miles, with 980 feet of elevation gain. The attribute table looks clean. The problem is that the original track log was collected in late February under typically stable conditions. When I walked this route in mid-January with recent storm loading, the final approach crosses a known avalanche fan that the dataset marks as passable but doesn't flag for size or aspect dependencies. I carried beacon, probe, and shovel and traversed the lower third on the bench instead of committing to the direct line shown in the shapefile. The workaround I use is to overlay the Nelson route layer on top of a current WSLFB avalanche forecast polygon for the specific wilderness area. If any segment of the route falls inside a CONSIDERABLE rating or higher for the relevant aspect band, I manually offset the track using the built-in editing tools in ArcGIS Pro or QGIS. This adds about twenty minutes of planning time but prevents the kind of hesitation you get when you're actually on the ridge and second-guessing the line.
Get the Full Details
Common Pitfalls That Trip People Up
The biggest issue I see is assuming the route points connect as straight lines between waypoints. They don't. The actual travel path interpolates through terrain you can't see from the point data alone. You need the underlying DEM to verify that no segment crosses a cliff band or an alpine bowl that would be impassable in deep snow. The dataset includes a landcover raster, but it's dated and doesn't capture recent timber harvests that opened up new traverse options or forced old routes into steeper ground. Another thing people miss is the date stamp on each route entry. The LAST_UPDATE field tells you when the track was last verified in the field. Several routes in the southern portion of the dataset, near the Snoqualmie Pass area, haven't been field-verified since 2019. Lodgepole beetle kill and windthrow in those corridors have changed the actual travel conditions significantly. I cross-reference those older entries with recent satellite imagery from the WA DNR orthophoto viewer before trusting the routing.
What This Data Won't Do For You
It doesn't include turn-by-turn navigation cues. You need to load the shapefile into a compatible GPS unit or offline mapping app and set up breadcrumb tracking yourself. The coordinate precision is good to within about three meters under open sky, but tree cover in the lower forested sections can degrade that to ten or fifteen meters on consumer-grade receivers. That's acceptable for route following but not for finding a specific trail junction in whiteout conditions. The dataset also doesn't cover the eastern Cascades. If you're looking for snowshoe routes past the divide, you'll need to supplement with data from the Okanogan-Wenatchee National Forest winter recreation layers or the USFS backcountry routing project for that region. The Nelson dataset stops at the crest and doesn't extend into the Alpine Lakes Wilderness eastern side.
Practical File Handling Notes
When transferring the data to a handheld device, convert the shapefile to GPX first. The native projection doesn't translate well to most GPS units and causes track display issues. Use a tool like GPSBabel to handle the conversion. Set the output to WGS84 and preserve the attribute fields so you can still sort by difficulty rating or elevation gain on the device. The conversion takes roughly forty-five seconds for the full dataset on a modern machine. If you're working in the field and need to annotate a route with your own observations, create a separate GeoJSON layer rather than modifying the original shapefile. The Nelson files use a coding scheme that other backcountry apps don't always recognize, and mixing formats in the same file corrupts the attribute relationships. I keep my own notes in a parallel layer that I merge back into the master only after I've verified the changes against the source data. The dataset is free to use but carries the standard disclaimer that it's intended for planning purposes and doesn't replace on-the-ground hazard assessment. That's fair. The data is valuable, but it's a snapshot, not a live system. Track it, verify it, and don't treat any route rating as a guarantee of safe passage in conditions you haven't personally checked.
