For much of the month, cool western weather limited the rate of melting snow. By May 1, the average water equivalency of the Sierra Nevada snowpack stood near 50 inches, according to the California Department of Water Resources, down about a foot from the seasonal peak of 62 inches. In late April, however, sudden heat led to increases in western streamflow and local flooding, as well as corresponding dam releases. Seasonably dry weather prevailed during April in much of California, the Great Basin, and the Southwest, while occasional showers stretched from the Pacific Northwest to the northern Rockies. Farther east, snow was also slow to melt in parts of the north-central United States, helping to hold April temperatures 5 to 7°F below normal in North Dakota locations such as Bismarck, Dickinson, and Minot. When the melt season finally began, moderate to major flooding was observed along parts of the Red, James, and Big Sioux Rivers. Significant flooding also occurred in the upper Mississippi Basin, where top-three crests were reported in locations such as La Crosse, Wisconsin, and Dubuque, Iowa. In those Mississippi River cities, higher crests were reported only in April 1965 and 2001.
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