The northern California Current System is impacted by two primary freshwater
sources: the Strait of Juan de Fuca and the Columbia River. The Columbia is frequently
bidirectional in summer, with branches both north and south of the river mouth
simultaneously. We describe the interaction of these two warm Columbia plumes with
each other and with the colder plume originating from the strait. The interactions occurred
when a period of strong downwelling-favorable winds and high Columbia River
discharge was followed by persistent and strong upwelling-favorable winds. The
northward plume that developed under the downwelling winds extended over 200 km
along the coast to the Strait of Juan de Fuca and into the strait. The plume subsequently
wrapped around Juan de Fuca Strait water in the counterclockwise seasonal eddy just
offshore of the strait. Inspection for similar wind and outflow conditions (>0.15 N m¯²
and 10⁴ m³ s¯¹, respectively) suggest that these events might have occurred in roughly
half the years since 1994. Surface drifters deployed in the Columbia plume near its origin
tracked this plume water northward along the coast, then reversed direction at the onset
of upwelling-favorable winds, tracking plume water southward past the river mouth once
again. ‘‘Recent’’ (~1–2 day old) and ‘‘Aged’’ (>14 day old) plume water folded around
the newly emerging southwest tending Columbia plume, forming a distinctive ‘‘sock’’
shaped plume. This plume was a mixture of ~10% ‘‘New’’ (<1 day old) water
and ~90% Recent and Aged water from prior north tending plumes