West Coast Upwelling Explained for Anglers

Short version: along the West Coast, wind pushes surface water offshore and cold, nutrient rich water rises to replace it. That upwelling cools the surface, lights up the chlorophyll, and builds the food chain that pelagics follow. Learn to read it and the whole season makes more sense.

What upwelling actually is

The West Coast runs north to south, and in spring and summer the prevailing wind blows from the north. Because of the way wind driven water turns relative to the wind, that northerly wind pushes the surface layer away from the coast and offshore. Water has to come from somewhere to replace it, and it comes from below: cold, nutrient rich water rises up along the coast. That rising is upwelling.

Two things happen when it does:

• The surface gets colder. Upwelled water is deep water, so the nearshore band cools off, sometimes sharply, during a strong upwelling push.
• The water gets more productive. The deep water carries nutrients. Bring those nutrients into the sunlit surface layer and phytoplankton bloom, which turns the water green and starts the food chain.

That combination, cold and green, is the signature of upwelling, and it is exactly what the temperature and chlorophyll charts show.

Why anglers should care

Upwelling is the engine of West Coast fishing. Phytoplankton feed the small stuff, the small stuff feeds the bait, and the bait draws the predators. A season with healthy upwelling tends to be a productive one. But upwelling also sets up the edges you actually fish.

The cold, green upwelled water does not spread out evenly. It forms a band along the coast, and offshore of that band sits warmer, cleaner blue water. Where the two meet you get a temperature break and a color seam stacked on top of each other. That is a high percentage edge, and it is upwelling that built it.

• Temperature break: the line between the cold upwelled water and the warm offshore water.
• Color seam: the green to blue line where productive water meets clean water.
• The target: where those two edges overlap, often with structure underneath.

How to read upwelling on the charts

Here is how to turn the science into a plan for grounds like the Bay Area, Northern California or Southern California.

1. Start with SST. Look for the cold band hugging the coast and the warmer water offshore. The break between them is your first target line. See how to read a temperature break. 2. Overlay chlorophyll. The upwelled band usually reads green and productive. Find the green to blue seam and see where it lines up with the temperature break. The compare tool puts both layers side by side. More in chlorophyll charts explained. 3. Watch it move. Upwelling pulses with the wind. A strong northerly blow strengthens it and pushes the cold band wider offshore. When the wind relaxes or turns, the cold water can slide back toward the beach and the warm water pushes in. Step through recent days to see which way the edge is trending. 4. Check the currents. ReelTemps doesn't draw a current layer, so use the free IOOS HF radar maps to see which way the surface water is being pushed. That helps you predict where the edge goes next. 5. Find the structure. Upwelling is strongest where current meets terrain. A break sitting on a point, a canyon or a bank is usually better than the same break over flat bottom. See shelf breaks, canyons and seamounts.

Relaxation and the warm water push

Upwelling is not constant. It comes in pulses tied to the wind, and the periods between pulses matter just as much.

• During a strong upwelling event, expect a cold, green, wide nearshore band and the fishable edge pushed well offshore.
• During relaxation, when the wind lays down or switches, warmer offshore water slides back toward the coast. That moving front can be a hot edge on its own, and it often brings warmer water species closer in.

Learning this rhythm for your grounds is most of the game. Many West Coast seasons are really a series of upwelling pulses and relaxations, and the fish follow the edges those create.

Ground truth it with the buoys

The charts show the surface from space, and on the West Coast the buoys are a great reality check during upwelling, when nearshore temperatures can change fast.

Satellite and in water readings can differ, especially in a rapidly changing upwelling band, so check the nearest buoys for real in water temperature and wind before you commit. See ground truth SST with buoys.

The takeaway

Upwelling explains why the West Coast turns cold and green when the north wind blows, and why that is good news for fishing. It builds the food chain and it builds the edges. Read the cold band, find where it meets the warm blue water, confirm the color seam and the structure, and watch how the wind moves it all. Pull up your region on the charts and start watching the pattern. Nothing is guaranteed, and conditions and seasons vary, but anglers who understand upwelling read the West Coast far better than those who do not.

Not for navigation.