Total precipitation during the 1990 water year was about 107 percent of normal in western Washington and about 95 percent of normal in eastern Washington. Tot total precipitation for the water year ranged between about 89 and 116 percent of normal throughout the State. Precipitation during September was the farthest below normal for a month when the monthly total was about 14 percent of normal in western Washington and about 3 percent of normal in eastern Washington. Monthly precipitation was the farthest above normal during June in western Washington, and during May in eastern Washington, when monthly totals were about 190 and 215 percent of normal, respectively.

Rainfall in western Washington was less than 75 percent of normal during the months of December, July, and September. It was near normal during October, March, April, and May, and was more than 125 percent of normal during November, January, February, June, and August.

In eastern Washington, precipitation was less than 75 percent of normal during the months of December, March, and September. It was near normal during October, November, January, February, and April, and was more than 125 percent of normal during May, June, July, and August.

The annual mean runoff was near or above normal in western and northeastern Washington, and near or below normal in southeastern Washington during the 1990 water year.

During the 1990 water year, three significant flood events occurred in western Washington. The flooding during November 9 to 11 was limited mainly to the Nooksack and Skagit River basins. Peak flows at gaging stations in these basins had recurrence intervals of up to 50 years. During December 4-6, widespread flooding occurred on many streams on the Washington coast and on streams draining into the central and southern Puget Sound. Peak flows with recurrence intervals of up to 25 years occurred. During January 9-12, widespread flooding occurred south of Seattle and into Oregon. Peak-of-record flows were recorded at some gaging stations in the Chehalis River basin with recurrence intervals of 100 years or greater. (A peak flow that has a recurrence interval of five years can be expected to be exceeded once in five years on the average.) The annual peak flows at most gaging stations in eastern Washington had recurrence intervals of up to two to five years.

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