Will El Niño help the Lake Mead water level?

Not reliably. In 46 winters of SNOTEL records, 1981 through 2026, the Upper Colorado River Basin's April 1 snowpack showed no consistent link to El Niño or La Niña: El Niño winters ran from 61% to 139% of the 1991-2020 median, La Niña winters from 58% to 158%, and the correlation between a winter's ONI and its snowpack is effectively zero. That snowpack is where most of Lake Mead's water starts, and even a big year reaches the lake only after Lake Powell, upstream, takes its share.

What El Niño and La Niña are

El Niño and La Niña are the warm and cool phases of a swing in sea-surface temperatures across the central and eastern tropical Pacific. NOAA's Climate Prediction Center measures it with the Oceanic Niño Index (ONI), a three-month average of the temperature departure in the Niño 3.4 region: +0.5°C or warmer marks El Niño conditions, -0.5°C or cooler La Niña.

The pattern NOAA describes for the United States is a southern one. In an El Niño winter the jet stream tends to shift south and stretch east across the southern US, and most of the strongest events have brought wetter-than-average weather to some part of the South, NOAA's Nat Johnson wrote in 2023. The typical La Niña pattern is the same map with the signs flipped. The Upper Colorado's snow falls in the middle of that map, on the mountains of Colorado's Western Slope, Wyoming, Utah and northern New Mexico.

What the record shows

The Upper Colorado River Basin snowpack page reads the basin the standard NRCS way: the snow water equivalent at every SNOTEL station in the basin, summed and divided by the sum of those stations' 1991-2020 medians for the date. Applied to April 1 of each year, the conventional date of the seasonal peak, the same method gives 46 readings, from 55 reporting stations in 1981 to 114 in 2026. Sorting each winter by its December-to-February ONI gives three groups:

• El Niño winters (15): a median of 101% of normal on April 1, from 61% in 2015 to 139% in 2019. Nine came in above 100% and six below.
• La Niña winters (16): a median of 108%, from 58% in 2012 to 158% in 2023. Ten above 100%, six below.
• Neutral winters (15): a median of 89%, from 27% in 2026 to 145% in 1993. Seven above 100%, eight below.

Across all 46 winters the correlation between the winter ONI and April 1 snowpack is -0.01, so knowing the ONI says essentially nothing about the snowpack. The strongest events make the same point. The five winters with an ONI of +1.5 or higher came in at 133% (1983), 91% (1992), 107% (1998), 100% (2016) and 113% (2024). The three La Niña winters at -1.5 or lower came in at 106% (1989), 86% (1999) and 134% (2008). Paul Miller, a hydrologist at NOAA's Colorado Basin River Forecast Center, told Newsweek in August 2026 that "there is no correlation between El Niño, and other ENSO events," and the basin's winter snowpack.

Worked example: three winters and Lake Mead

• 2023, a La Niña winter (ONI -0.55). April 1 snowpack reached 158% of median, the largest in the record. Lake Mead ended 2023 at 1,068.05 feet, 23.23 feet above its level at the end of 2022.
• 2024, a strong El Niño winter (ONI +1.84). April 1 snowpack was 113% of median. Lake Mead ended the year at 1,063.29 feet, 4.76 feet lower than a year earlier.
• 2026, a neutral winter (ONI -0.39). April 1 snowpack was 27% of median, the smallest in the record, and Lake Mead fell below its July 2022 low on Aug 6, 2026.

The middle case shows why an above-median snowpack does not guarantee a higher lake. Reclamation sets the volume Glen Canyon Dam releases from Lake Powell each water year by operating tiers tied to Powell's elevation, so a good spring raises Powell first and reaches Lake Mead only through those releases. Miller made the same point: much of a big year's water "will also be stored in Lake Powell."

When a strong El Niño is forming

NOAA's ONI reached +2.16 for July through September 2026. The five strongest El Niño winters in the record ran from 91% to 133% of median on April 1, a range wide enough that it points to no single outcome. The snowpack chart at the top of this page fills in from the first storms to the April peak, and that reading, not the ONI, is what Lake Powell and Lake Mead respond to. Lake Mead water level by year has the lake's level for every year since 1935.