April 2025 snow summary
- Snow-covered area across the western United States was 100 percent of average for April.
- Snow cover duration was just above the twenty-fifth percentile of the 25-year satellite record.
- Snow albedo, also known as snow brightness, started low in early April and decreased throughout the month, and was below the twenty-fifth percentile of the 25-year satellite record at the end of the month.
- Snow water equivalent (SWE) decreased in every state in the western United States, with coastal states showing the largest decreases at individual stations.
Overview of conditions
Snow-covered area in April across the western United States was almost exactly on the long-term average, at 244,000 square kilometers (94,000 square miles) of snow cover, ranking twelfth in the 25-year satellite record (Table 1). Snow-covered area for April was 308,000 square kilometers (119,000 square miles) below 2023, the highest year, and 119,000 square kilometers (46,000 square miles) above 2015, the lowest April on record.
Table 1. April 2025 Snow Cover in the Western United States (Relative to the 25-Year Satellite Record)
| Snow-Covered Area | Square Kilometers | Square Miles | Rank |
|---|---|---|---|
| April 2025 | 244,000 | 94,000 | 12 |
| 2001 to 2024, Average | 244,000 | 94,000 | -- |
| 2023, Highest | 552,000 | 213,000 | 1 |
| 2015, Lowest | 125,000 | 48,000 | 25 |
| 2024, Last year | 261,000 | 101,000 | 10 |
While snow cover assessed over the entire study region was very close to average, it was below average in New Mexico (48 percent of average), Arizona (72 percent of average), California (90 percent of average), Colorado (80 percent of average), Nevada (68 percent of average), Utah (88 percent of average), and South Dakota (30 percent of average) (Figure 1). Snow conditions were very close to average in Montana (97 percent of average), Washington (98 percent of average), and Wyoming (104 percent of average), contrasting with above-average snow cover in Idaho (117 percent of average) and Oregon (130 percent of average). These geographic patterns were also apparent in major river basins, with the lowest below-average snow cover in the Lower Colorado (50 percent of average), Rio Grande (75 percent of average), and Arkansas-White-Red (78 percent of average) basins. The Pacific Northwest (110 percent of average) basin was the only hydrologic unit code 2 (HUC2) basin with above average snow cover, corresponding to above average snow cover in Idaho and Oregon.
Conditions in context: Snow cover
As noted, total snow-covered area for April was near average (Figure 2, upper left). While storms in the first week increased snow-covered area to slightly above average, it then declined to fall below average. Regionally, low-elevation regions in Oregon and mountainous regions in Idaho had 20 to 60 percent above-average snow cover. By contrast, in Colorado, Utah, and southern Wyoming, snow cover fell 20 to 60 percent below average (Figure 2, upper right). California had above-average snow cover in the northern part of the state and below-average in the Sierra Nevada mountains, while Nevada had below-average snow cover overall.
Snow cover duration measured in days summed from October 1 to April 30 continued to increase (Figure 2, lower left). Snow cover duration at the end of April was near the twenty-fifth percentile. Regionally, snow cover duration in Arizona, New Mexico, Nevada, and Utah was well below average, and widespread areas had 60 to 100 fewer snow cover days (Figure 2, lower right). Wyoming also had below-average snow cover duration. Conversely, Colorado, Oregon, Washington, Idaho, and Montana had regions with 20 to 40 more snow cover days than average.
Average snow brightness, known as snow albedo, was close to the twenty-fifth percentile at the beginning of April, but sharply decreased until the middle of the month, caused by high temperatures and snowmelt (Figure 3, left). Albedo continued to decrease during the third and fourth weeks of April and was roughly 10 percent below average at the end of the month. Most mountainous areas had below-average albedo for April (Figure 3, right). In much of Colorado, Utah, Montana, and California, snow albedo was up to 20 percent below average.
Conditions in context: Snow water equivalent (SWE)
Snow water equivalent (SWE) conditions at the beginning of April were mixed with a range of average, below-average, and above-average SWE (Figure 4). Moderately to extremely low SWE prevailed in Arizona, New Mexico, southern Colorado, southern and central Utah, central Nevada, the Bighorn Range in Wyoming, lower-elevation stations in the Sierra Nevada in California, northwest Montana, and the Washington Cascades. SWE was near- or above-average in northern California, northern Nevada, the Front Range of Colorado, southern and eastern Oregon, and central Idaho.
SWE declined through April. Relative to average, conditions at the end of the month were drier compared to the beginning of the month. Many stations in northern California and the Sierra Nevada dropped to 0 SWE by April 30, as well as three stations in Arizona and six in northern New Mexico. Both Colorado and New Mexico experienced large decreases in SWE during April, as did the Washington Cascades (i.e. many dark red stations).
Decreases in SWE occurred across all states during April (Figure 5). Coastal states in particular had large SWE losses, with some stations in Washington, Oregon, and California losing more than 50 centimeters (20 inches) of SWE. Montana, Wyoming, Arizona, and New Mexico had the smallest decreases in average SWE, but in Arizona and New Mexico, this was largely because of low SWE at the beginning of the month.
