This is a weather story. I am writing this toward the end of April. Last night we had a 1/2 inch of rain and possibly more is forecast over the next week. These spring showers, although not particularly heavy, are most welcome, keeping the hills green and our creeks full. This April has been an interesting month, weather-wise, starting off cold and windy, then warm and still, and now rainy with light breezes.
What we haven't had are daily, unrelentingly strong spring winds. Normally by this time in April, they will have started in earnest. As the sailors in the Club know, they can rely on strong winds almost every day from mid-April to mid-summer and beyond. These winds are also very important for the natural world on coastal northern California.
After the spring equinox, the northern hemisphere receives more warmth and light. The mid-Pacific gyre, a huge swirling current and high-pressure zone, strengthens and moves north. At the same time the Central Valley heats up. As we all know, warm air rises, producing low pressure over a large area. In normal years, a strong pressure gradient forms and north-west winds blow inland to fill the void left by the rising air over the Valley.
Off our coast, we have a continental shelf that is about 30 miles wide. It ends with a steep escarpment that dives down thousands of feet. The water over the shelf is relatively warm and nutrient poor while in the depths below the escarpment, the water is very cold and nutrient filled, enriched by eons of dead stuff and other detritus falling to the ocean floor. The strong spring winds push the warm surface water off to the south and an upwelling from the depths occurs. The combination of rich water and stronger sunlight starts an explosion in the food chain beginning with single-celled phytoplankton which are eaten by zooplankton which are eaten by krill and other little invertebrates, then little fish and bigger fish and all the way to sharks and orcas. Historically, our coastline has been one of the richest fisheries in the world until it was decimated by over-fishing and other human effects. It is only one of five so-called upwelling zones in the world.
Another aspect of the winds: as the warm, humid winds from mid-ocean cross the cold California current, which is flowing down from Alaska and the Aleutians, they cool off and their humidity condenses into fog. For those of us who enjoy temperate days and cool nights, the fog is a welcome addition. It is also an important foundation for much of our local flora. Redwoods only thrive in the fog zone. Many of our other plants can only live in our cool moist summers. In Inverness, our water supply benefits from around ten inches of summer 'fog-drip' when the wet winds condense on the Bishop Pines and Douglas Firs along our ridge top.
However, during the last few years, the spring winds haven't been as strong as usual. The now-famous "ridiculously resilient ridge" of high pressure that has formed along the north Pacific coast has partially blocked our winds. Thus water temperatures at the Lighthouse have remained significantly warmer than normal and our fog-drip has been lower. Weather and climate experts are still hypothesizing why: perhaps El Nino/La Nina effects , the Pacific Decadal Oscillation and global warming.
What will happen this spring? Your guess is as good as mine. I'm hoping for big winds.