# How to read percent-of-median snowpack (and why it breaks at melt-out) > Percent of median compares today's basin snowpack to the 1991-2020 median for this same date, so 100 percent means a normal snowpack for the day. The catch is that near melt-out the normal itself falls to almost nothing, so the percentage blows up and stops being meaningful, which is why this site reports the season peak once the snow is nearly gone. _Updated Jul 21, 2026._ Percent of median is the headline snowpack number, and it answers one question: how does today's snowpack compare to normal for this exact date? A reading of 100 percent means the snowpack holds as much water as it typically does on this day. Above 100 is a fuller-than-normal snowpack, below 100 a thinner one. The normal here is the 1991-2020 median, a 30-year baseline. ## How the number is built This site uses the standard basin-index method that the NRCS uses. It adds up the current water content across every reporting station in the area, adds up those same stations' 1991-2020 medians for the date, and divides one total by the other. Summing the water content rather than averaging the percentages weights each station by how much water it actually holds, so a deep high-elevation site counts for more than a shallow valley one, and a brand-new station with no long-term normal never distorts the result. ## Why for-the-date matters The comparison is always to the same calendar date, and that is what makes it honest. A snowpack at 100 percent of median in January and one at 100 percent in April are both normal, but they are very different amounts of water, because the normal itself is far higher in April near the peak. Comparing today to today's normal, rather than to the seasonal peak, keeps the reading meaningful at any point in the year. ## The melt-out trap There is one time the percentage breaks, and it is worth understanding. As the snow melts out in early summer, the normal for the date falls toward zero. Percent of median is a fraction, and when the denominator shrinks toward nothing the fraction explodes. A trace of late snow sitting on a date whose normal is a tenth of an inch can compute to several hundred percent, which tells you nothing useful. A near-zero denominator makes the number meaningless, not dramatic. So this site suppresses the percentage once the normal snowpack for the date drops below a small floor. Instead of printing an absurd number off a near-empty normal, the page reports what the snowpack actually did this season: its peak water content and when it hit it. An off-season snowpack page here is dormant by design, not a data gap. It picks back up in the fall as the snow returns and the normal climbs back to a level where percent of median means something again. ## Worked example [Chart: Colorado snowpack (snow water equivalent)](https://the-waterline.com/snowpack/colorado) ([data](https://the-waterline.com/snowpack/colorado.md) — chart image: https://the-waterline.com/charts/snowpack/colorado/chart.png) On the chart above, the median line is the denominator behind the percentage. Watch how it climbs to an early-April peak and then falls to the floor by summer. While that line is high, percent of median is a solid read on the season. As it collapses toward zero in early summer, any percentage computed against it would be noise, which is exactly why the page switches to reporting the season peak once the snow is nearly gone. ## Related data + guides - [Snowpack tracker](https://the-waterline.com/snowpack) - [What is snow water equivalent?](https://the-waterline.com/guides/what-is-snow-water-equivalent) - [What is SNOTEL?](https://the-waterline.com/guides/what-is-snotel) - [Reservoir storage tracker](https://the-waterline.com/reservoir) ## Common questions ### What does 100 percent of median snowpack mean? It means the snowpack holds as much water as it normally does on this exact date, measured against the 1991-2020 median. Above 100 percent is fuller than normal for the day, below 100 percent is thinner. ### Why does the snowpack read blank or off-season in summer? The snow has melted out. Near melt-out the normal snowpack for the date falls to almost nothing, so percent of median would divide by a near-zero number and produce a meaningless figure. This site suppresses the percentage then and reports the season's peak instead, until the snow returns in the fall. ### Does 100 percent snowpack mean 100 percent runoff? No. Snow water equivalent is the water in the snow, but dry soils absorb the first melt, dust on the snow speeds it up, and some sublimates into the air. Snowpack is the starting point for a runoff forecast, not the runoff itself. This site reports the snowpack as measured and does not forecast runoff. ### What is the basin-index method? It sums the current water content across all reporting snow stations in an area, sums those same stations' long-term medians for the date, and divides the two totals. Summing rather than averaging weights each station by the water it holds, so a deep high site counts more than a shallow one. --- Canonical URL: https://the-waterline.com/guides/how-to-read-percent-of-median-snowpack