In mid-April, Washington State snowpack was near normal, while snowpack to the south was well above normal.
Then Washington experienced much warmer than normal temperatures in late April and May, as illustrated by the temperatures at Olympia below (normal highs are shown by the purple line)
The result of the warmth was a massive melt-off of the Cascade snowpack that has surged into local reservoirs, filling them to normal levels.
For example, consider the Yakima Reservoir system, so important for eastern Washington agriculture (see below). Over two weeks of May, the reservoirs went from below-normal to normal levels.
Seattle's snowpack in the watershed feeding its reservoirs is shown below. Wow. A precipitous decline!