NASA data helps Tacoma Power navigate snow drought

At Tacoma Power’s Cowlitz River project in southwest Washington, December’s rain arrived as a wall of Pacific moisture instead of a slow-release mountain snowpack. The atmospheric river produced one of the largest one-day inflow surges ever recorded at the hydroelectric project; months later, the utility was seeing peak daily inflows among the lowest on record. NASA satellite data is now helping Tacoma Power steer through both extremes.

The operational forecasts come from Upstream Tech’s HydroForecast, which combines weather forecasts and river measurements with NASA observations of snow cover and vegetation. The data comes from VIIRS — the Visible Infrared Imaging Radiometer Suite — aboard the Suomi-NPP satellite. Those observations cover entire watersheds, including places where ground monitors are sparse, and the forecasts are updated every two hours.

The need was unusually sharp during the winter of 2025-26. January, February and March each had the lowest Western snow cover for that month in NASA’s MODIS satellite record since 2001. On the Cowlitz, snowpack stayed at 20% to 50% of normal after unusual warmth turned more precipitation into rain. When rainfall tapered off, Washington placed every watershed under a drought emergency on April 8.

Tacoma Power used the short-term model to anticipate how much water would reach its project during the December storm, while its largest hydroelectric project supplies enough electricity to serve more than 151,000 homes each year. As spring brought weaker runoff, operators used the seasonal model to track the risk and kept reservoirs higher than usual to preserve water for summer. That strategy left less room for another major storm, so the utility continued checking short-term forecasts and remained ready to adjust operations.

So what changes in practice? Water managers gain an additional, frequently refreshed view of conditions beyond the next gauge or snow station: one that can support storm preparation, reservoir releases, hydropower generation and drought planning. Upstream Tech says tests across multiple basins found that adding snow and vegetation observations increased forecast skill. Tacoma Power still combines the forecasts with measurements and operator judgment, with public safety and operating requirements in the loop.