For us, zonal flow is the term we use for when a strong jet stream is moving due east across the Pacific Ocean and plowing straight into the Pacific Northwest. This pattern usually brings several storms one-after-another in rapid succession through the area.
Most of the time, it means storms can be blowing through the area every 24-36 hours. And even between storms, with the moist flow, we stay cloudy with frequent showers between storms, making it difficult to tell when one storm stops and the next begins.
These patterns can last for up to a week or even 10 days, and certainly help to give Seattle its rainy reputation.