When we say wind is an "intermittent" resource, we mean it. This Bonneville Power Administration graph shows the output of wind generation for a seven-day period and how quickly it can "ramp" up or down. As you can see, the afternoon of April 2 shows quite a large spike. It gives you a good idea of how quickly this resource can affect the system, and why it's so important to have access to other resources that can be quickly decreased or increased to compensate for its unpredictability.
The Council's Wind Integration Forum has been working on solving some of the challenges to adding large amounts of this resource into the region's power system.