Snowpack, Drought and Water Supply Forecasts in Oregon: How to Read Them

In most of eastern Oregon, the summer water supply is decided in the mountains between November and April. Snow piles up in the Blue Mountains and the Cascades, melts slowly through spring, and feeds the rivers, reservoirs and canals that irrigators draw on through August. Reading the snowpack and the forecasts built on it is a basic skill for anyone who farms, manages a district or simply wants to know how tight the coming season will be.

Why snow carries so much weight

The Natural Resources Conservation Service (NRCS) estimates that 50 to 70 percent of the water supply in the West comes from melting mountain snowpack. Snow works as a reservoir that fills in winter and releases in late spring, just as irrigation demand climbs. When snow is thin, or melts early, rivers peak sooner and drop lower by midsummer.

Oregon's typical peak snowpack falls between about March 11 and March 30 for most major basins, according to NRCS Oregon. By April 1, the picture for the year is usually set.

How snow is measured

NRCS has run a formal, cooperative Snow Survey and Water Supply Forecasting Program since 1935 for the western U.S. Its history page notes that the first federal cooperative snow survey within the Soil Conservation Service, NRCS's predecessor, formed in 1939, and that during the 1970s new radio technology let sites report automatically.

Two kinds of measurements feed the system:

• Snow courses. Fixed routes where crews take manual samples, a practice NRCS Oregon traces back to survey crews of the mid-1930s.
• SNOTEL stations. Automated sites that measure snow water equivalent and precipitation and transmit by satellite. NRCS reports more than 850 SNOTEL sites and nearly 50 scaled-down SNOLITE sites across the West.

The key number is snow water equivalent (SWE): the depth of water you would get if you melted the snowpack in place. Two feet of fluffy snow and two feet of dense spring snow can hold very different amounts of water, so SWE, not depth, drives the forecasts.

Reading a snowpack report

NRCS Oregon publishes a daily SNOTEL update and a monthly Water Supply Outlook Report from winter into spring. Most numbers are given as a percent of median, compared against the 1991–2020 period. A few terms to know:

• Percent of median SWE. How today's snowpack compares with the typical value for the date.
• Water-year precipitation. Total since October 1, the start of the water year.
• Basin index. A roll-up of several stations or reservoirs for a basin.
• Meltout date. When a station's snow is gone. Early meltout means less water late in the season.

Reservoir storage appears in the same report. For the Umatilla, Walla Walla and Willow basin, NRCS lists Cold Springs, McKay and Willow Creek reservoirs, with storage both as a percent of capacity and as a percent of median.

Reading a water supply forecast

Forecasts estimate the volume of streamflow at a gauge over a set period, usually April through September, in thousands of acre-feet. Instead of a single number, NRCS gives a range of exceedance probabilities. The report's legend spells them out: at the 70 percent level, there is a 70 percent chance flows will exceed that volume; at 50 percent, an even chance; at 30 percent, a 30 percent chance; and so on toward the dry and wet extremes.

In practice:

• The 50 percent value is the central forecast.
• The drier values (70 and 90 percent exceedance) are the conservative numbers to plan around if a shortfall would be costly.
• The wetter values (30 and 10 percent) show the upside if spring turns wet.

Here is how that looked for the Umatilla River at Pendleton on March 1, 2026, a very poor snow year:

Exceedance level	April–September volume (thousand acre-feet)
Dry end of range	45
70%	67
50%	85
30%	105
Wet end of range	138

The same report put April–September forecasts across the Umatilla, Walla Walla and Willow basin at 52 to 76 percent of median.

Forecasts shift month to month as snow accumulates or melts and as spring rain arrives. A March 1 forecast is a starting point; April 1 is usually far more reliable.

2026: a case study in snow drought

Water year 2026 is a useful example because it was so extreme. On March 1, statewide SWE was the second lowest on record for Oregon's SNOTEL network, which dates to 1981. NRCS attributed it largely to persistent warm temperatures in the mountains from November to February, when much of the precipitation fell as rain even at high elevations. Many stations and snow courses reported at or near record lows.

For the Umatilla, Walla Walla and Willow basin, NRCS reported on March 1:

• basin snowpack at 37 percent of median;
• water-year precipitation at 87 percent of median;
• Cold Springs Reservoir at 58 percent of median storage and McKay at 63 percent.

Note the gap between precipitation and snow. The basin received most of its normal moisture, but not as snow. By mid-March, NRCS reported that four SNOTEL stations in the Umatilla and John Day basins had melted out 34 to 70 days earlier than normal. Rain can lift streamflow for a few days. It does not refill a snowpack that would have fed the river in June.

Early melt has other causes too. Utah's Great Salt Lake strategic plan cites University of Utah research estimating that dust blown off the exposed lakebed made the 2022 snowpack melt 17 days earlier than normal. Our guide to what the shrinking Great Salt Lake means for Oregon looks at that link and at Oregon's own saline lakes.

How drought is declared in Oregon

A state drought declaration is separate from a general emergency declaration. OWRD describes a three-part process under ORS chapter 536:

1. A county or tribe asks the state for a drought declaration.
2. The Water Supply Availability Committee, chaired by OWRD and made up of state and federal science and emergency agencies, reviews conditions. The Drought Readiness Council, co-chaired by OWRD and the state's emergency management office, weighs impacts and recommends to the Governor.
3. The Governor decides whether to issue an executive order.

In 2026, Governor Tina Kotek declared drought in Baker, Deschutes and Umatilla counties on March 26, the first declarations of the year. Morrow County followed in a second order in April that covered six counties. By mid-July the Governor had issued six drought orders, and 21 of Oregon's 36 counties were under drought emergency status. A state hydrologist compared the year to 2015, when 25 of Oregon's 36 counties received drought emergency declarations.

What a declaration changes for water users

A declaration lets OWRD offer short-term emergency tools in the declared area, with expedited review and reduced fees:

• Emergency water use permits, most often allowing groundwater use in place of a surface right, valid for up to one year or the term of the declaration;
• Temporary drought transfers of use, place of use or point of diversion;
• Temporary instream leases and substitutions of a supplemental groundwater right for a primary surface right;
• Temporary exchanges, such as using stored water instead of direct flow.

The Water Resources Commission can also adopt temporary rules giving human consumption and stock water preference over other uses regardless of priority. And under ORS 540.610, a declared drought year does not count toward the five-year forfeiture period, provided the holder had a working system and was ready to use the full right.

OWRD warns that in a severe year, regulation of water rights tends to reach older priority dates than normal, so users who are rarely shut off may be regulated back or off.

A quick checklist for the season

• Check the NRCS SWE map and your basin's percent of median in January, February and March. If you need streamflow or well records to go with it, our guide to researching Oregon water issues lists the state and federal databases.
• Read the March 1 and April 1 Water Supply Outlook Reports, and plan to the 70 percent exceedance value if a shortfall would hurt.
• Watch reservoir storage alongside snowpack; low carryover storage compounds a poor snow year.
• Talk with your irrigation district or local watermaster early about likely regulation.
• If your county is declared, ask OWRD about emergency permits or transfers before you need them.

Local irrigation suppliers, well drillers and agronomists tend to be busiest in exactly the years when this checklist matters most, so early planning pays.