Snow Levels

Broad Overview

The Snow Water Equivalents page gives you a good high level overview of where snow levels are at historically. Useful in the winter/spring to try and figure out when summer in the alpine will start. The "snow" menu at the top has a few more options as well as particular sensor data. You can also see snow levels from the current year plotted against a few others of note.

The forest service has a snow depth tool but it is low enough resolution that it can easily underestimate snow levels if it samples rock outcroppings, tree cover, etc. It's useful, but should be taken with a few grains of salt, along with the mapping applications that import this layer.

The NOAA's regional snow analyses for the Sierra Nevada has a lot of high level snow and water information in graphical form, though it's better used to understand trends or an overview vs a specific location.

Recent Sentinel 2 Satellite Imagery

For medium-high resolution satellite imagery that is 4-6 days old, there's a number of ways to get Sentinel data.

• EO Browser is another free offering from Sentinel Hub, which has more options to it if you want to play around a bit. Basically navigate around on Topo (check contours, labels, and roads in the layers menu) or use the search field up top to go where you want, click the large green search button in the EO Browser pane on the left, and then choose the most recent pass that doesn't have a lot of cloud cover. I prefer this over Sentinel Playground. For either it's good to go through their tutorial / walkthrough as the UI is complex.
• The Sentinel Playground is another free offering. To make it easier to find the area you're interested in, you can turn all the satellite images off with the datasets pull down on the right side. That then let’s you navigate much easier on a base map - it’s not quite a topo map - but much easier than trying to navigate with the satellite image on. In order to see what date the imagery is from, go to the left menu sidebar, switch from rendering to effects, and toggle "show aquisition dates" and date overlays will overlay on the slices of images.
• USGS's Sentinel2Look viewer lets you filter for cloud cover and view historical data from 2015.
• You can integrate Sentinel 2 data into Caltopo with their $50/year plan, which is covered in this blog post by them. This is handy for getting an idea if it overlays a specific trail etc vs the area it's in.
• GaiaGPS has a clever map layer called "FreshSat" which tries to mix the best of Sentinel 2 and Landsat data. While this is theoretically better than the above, there may be some contrast and lineup issues. It's available for all users on the web, and on the mobile app with a Gaia GPS premium membership. Their cloud detection is less sophisticated than the sentinel-hub site, and is often out of date, and you can't go back to previous scans which is often helpful.

(Eastern) Sierra Avalanche Center

ESAC observations page with trip reports)covers the region from Lee vining down to Bishop, and SAC (observations page with trip reports) covers the area between Ebbetts and Yuba. The forecasts pages on both are also worth checking, as well as general information regarding avalanche safety. Avalanche.org shows all forecsat areas in the US.

Monitoring station data (quirky)

Individual monitoring stations give much more specific (and accurate) data than satellite based ones, but there aren't that many of them. High altitude ones can not be reporting, and low altitude ones aren't that useful. YMMV.

The USDA's snowtel map shows data from monitoring stations across the Sierra Nevada, some at a respectable altitude. Viewing this with overall averages by basin You can also get a listing of the stations for California.

For more detailed information to dig into, check out the California Data Exchange Center for individual snow levels in various locations. You can also search for individual sensors by river basin or check a list of active snow sensors. They publish bulletins on the second week of February, March, April, and May containing forecasts of the volume of seasonal runoff from the state's major watersheds, and summaries of precipitation, snowpack, reservoir storage, and runoff in various regions of the State.

Gaia GPS premium members can get snowtel overlays showing recent changes when they have an active internet connection.

Other resources

GISsurfer is a little janky, but allows you to play around with a ton of GIS layers including snow and water.

For water levels, as opposed to snow, Dreamflows has gathered up stream flow sensors in California & Nevada and done a good job of providing at a glance comments on it to put the data in context. Mostly lower elevation larger rivers or reservoir related, but could be useful.