Learn about snow and your water supply

1. #1: What is snowpack?
Snowpack is the total amount of snow on the ground. The “pack” in snowpack refers to snow
being packed down as new snow falls on top of old snow.
Denver Water photo: Jones Pass

2. #2: Why do we care about snowpack?
Most of the Denver area’s water supply comes from mountain snowpack that melts. The water
(also known as “runoff”) runs downstream and is captured in our reservoirs.

3. #3: What do we look for in snowpack?
Depth of the snow is not as important as how much moisture is in the snow. Experts measure
“snow water equivalent” to judge how much water the snowpack will yield. Snow water
equivalent is the depth of water that would result if the snow were melted. Which begs the
question….
Denver Water photo: Winter Park

4. #4: How do we measure snow water equivalent?
It’s typically measured one of two ways. We can manually measure it by capturing snow in a
sampling tube, weighing the snow and using a formula to convert weight to snow water
equivalent. Or…
Denver Water photo: Winter Park

5. #4: How do we measure snow water equivalent?
Automated SNOTEL sites maintained by the Natural Resources Conservation Service of
Colorado measure the weight of snow captured on special sensors and convert it to snow
water equivalent.
Photo courtesy of NRCS Colorado

6. #5: How do we determine if snowpack is “normal”?
We compare current conditions to the same date historically. Snowpack is typically expressed
as a percentage. (Those are the numbers you see on snowpack maps.) A number below 100
percent means that snowpack is below the historic normal for that date; a number above 100
percent means above-normal snowpack.
Denver Water photo: Jones Pass

7. #6: Where do we capture snowpack runoff?
Denver Water captures runoff from snowpack in the Upper Colorado River and Upper South
Platte River basins. But we don’t capture runoff everywhere in those basins. The snowpack
must be in areas above points where we divert water to flow into our reservoirs.

8. #7: What other factors affect snowpack?
Sun, wind and dust are all factors. Dust makes snow surface darker, causing snow to absorb
more of the sun’s energy and melt faster. Strong, dry winds can blow snow off mountain peaks
before melting occurs. And early, warm temperatures can dry out the ground, making it more
likely to absorb snowpack runoff before the water ever reaches our reservoirs.
Photo courtesy of Center for Snow and Avalanche Studies, Silverton, Colo.

9. #8: What happens to snowpack when it rains?
It depends on the temperature of both the snowpack and the raindrops. Sometimes the
raindrops freeze when they hit the snow, and the snow water equivalent increases. But if the
rain is warmer than the snowpack, the rain can cause melting.
Denver Water photo

10. #9: When should we closely monitor snowpack?
Any precipitation any time helps the Denver area’s supply. Heavy, early winter snows can
provide a cushion should weather turn dry later, but a wet spring can also make up for a dry
winter. We monitor the snowpack almost year-round, but our experts pay particular attention
as winter turns to spring, since March and April are typically our snowiest months.
Denver Water photo

11. To sum it up...
Regardless of the amount of snow in the Rocky Mountains in any given year, the water the
snowpack produces will always be an incredibly precious resource. We should understand
how our world is all connected and be efficient in our use of water.
Denver Water photo: Cheesman Reservoir