by Kyle Dittmer, CRITFC Hydrologist-Meteorologist
Starting on October 1, the new water year had a dry start then turned very wet (mid-November to New Years). After an unexpected very dry January we shifted back to a wet pattern and continue that mode to this day. We’ve had nine Atmospheric River events (formerly, “Pineapple Express”) that delivered much needed valley rainfall and mountain snowfall since November. These special weather events help mountain snowfall get caught up to near normal where we need to be before the seasonal snowmelt cycle (i.e., the Freshet) begins in May.
The seasonal rain/snow accumulation graphic (below) shows the return to very dry conditions. There has been high variability in the autumn-winter weather patterns so far.
At present we just had a “La Niña” event where Pacific Northwest winters were cooler than normal temperature with above normal rain/snowfall. This means that the amount of spring snowmelt runoff will be near-to-above normal. NOAA weather forecasters predict a transition to a neutral state now and continue into summer (95-99% chance).
The timing of the river runoff is likely to be near historic norms: late-April through late May for the tributaries and early June for the mainstem Snake and Columbia rivers. A separate article in May will give more details about how the spring runoff will play out. This snowmelt runoff feeds the river flow which helps the fish migrate down the river and out to the ocean. North Pacific Ocean conditions along the Pacific Northwest and Alaska coastlines are more favorable for salmon survival now due to more coastal upwelling from the deep ocean.
There is still concern about the lingering effects of the multi-year drought (see graphic below). Any existing dry soils will need to be replenished before any snowmelt runoff may occur. This means that the expected tributary river runoff may be a little lower than expected in some areas.
The table below shows the change in snowpack, as measured by “Snow Water Equivalent” (i.e., the liquid water content of the snow) for select tributaries that are of interest to tribal fishery program managers:
The change from January 1st to February 1st shows the unusual mid-winter dry-spell. The March and April updates have benefited from more mountain snowstorms.
The figure (see graphic below) shows the current state of the region’s Water Supply Forecasts. The eastern Oregon and southwestern Idaho basins show the most improvement. The Oregon Cascades are near normal and there has been improvement in the Washington Cascades. Current north Oregon Cascades snow level is 4500 feet. We just passed the peak in the seasonal accumulation of Pacific Northwest snowpack.
Snowpack, along with monthly and seasonal precipitation and current river flow, are the key components that are used to calculate the seasonal Water Supply Forecast. This forecast is used by water management agencies – U.S. Army Corps of Engineers, BPA, and the U.S. Bureau of Reclamation – to determine how much water is released for power, irrigation, and fish. The latest water supply forecast (as of April 29): Columbia River at The Dalles is 84% of normal for the April-July runoff period (NOAA/NWS’s ESP method).
(charts provided by NOAA/National Weather Service-Portland, updated on 29-April-2025)