A lot can happen during a winter storm. It can leave a mountain creek running high and the slopes above it nearly bare. Both are clues to what fell overnight. Rain can reach the creek within hours. Snow can stay on the mountain for months. For anyone who counts on that creek to feed a river or reservoir, they need to think about the time difference on when that water reaches there.

In much of the American West, mountain snowpack acts like a reservoir upstream of the dam. It builds up through winter. When warmer weather comes, the melted snow turning into ice feeds rivers in spring and summer. While rain can also add to the same rivers, most of the water may arrive well before the dry months. A winter precipitation total alone won’t tell you how much water is still sitting on the slopes.

What did NASA see during the 2026 Western snow drought?

NASA Earth Observatory found that most parts of the West had received average or above-average precipitation in fall and early winter. Yet many mountain areas had unusually little snow. Warm conditions meant more precipitation fell as rain, while some places simply got too little precipitation.

NASA satellite data showed on January 15, 2026 that the snow covered about 142,700 square miles across the West. It was the smallest area for that date in a satellite record going back to 2001. A heat wave in late March sped up the loss of snow cover.

In the Upper Colorado River Basin the amount of water stored in the snowpack peaked around mid-March. The peak came about four weeks earlier than usual. By the time the basin would typically have the most water stored as snow the 2026 snowpack had already passed its peak.

What happened at Lake Powell by summer?

In July, the U.S. Bureau of Reclamation put Lake Powell’s inflow at just 9% of average for the month after adjusting for upstream water operations. In August, both Lake Powell and Lake Mead reached record-low water levels. The weak snow season deepened a shortage in a river basin that had already endured more than two decades of drought.

Why can’t dams save all the winter rain?

Some of it can be saved. At California’s Lake Oroville, operators release water in winter and early spring to leave room for runoff from later storms. As summer approaches, they shift toward holding as much water as they can while still meeting water delivery and environmental requirements.

The mountain and the dam do different jobs. Snow on the slopes can wait for warmer weather. A reservoir receiving a rush of winter rain has to manage that water as it arrives.

FAQs

What is a snow drought?

A snow drought happens when there’s unusually little snowpack for the time of year. It can happen when storms bring too little precipitation or when warm weather makes more of it fall as rain.

Can winter rain still help water supplies?

Yes. Rain can refill reservoirs and recharge groundwater. Its value depends in part on where it falls and how much can be captured or stored.