You’ve probably noticed — it hasn’t been raining much lately. And now that we’re well into December, the averages say it ought to be. What’s going on?
As those who pay attention to our local weather cycles know, Tulare County falls within the extremely variable borderland between the wet winter climate of the Pacific Northwest and the equally dry winter climate of northern Mexico. Because of this geographic fact, our winters vary enormously one year to the next. Some are wet — others very dry.
Scientists have been searching for decades for the patterns that control this variability. They’ve found some useful clues, but forecasts remain far from foolproof.
The most broadly followed clues have to do with the ocean temperature patterns we call El Niño and La Niña. Simply put, El Niños see critical parts of the Pacific Ocean warmer than average and often are quite wet in California. When La Niña conditions predominate, the ocean is cooler and California tends toward the dry side.
Unfortunately, however, it’s not always that simple. Strong El Niño years are reliably wet, but moderate and weak events are just as often dry. Moderate La Niña events are often dry, but occasionally, like last year, quite wet.
Last fall, while under the sway of a La Niña forecast, we prepared for a dry season and found ourselves instead enduring one of the wettest winters in several decades. This year, the La Niña pattern again dominates, and the pattern is starting out dry.
As of the beginning of December we have received about half as much precipitation as fell last year to the same date. And last December was extraordinarily wet, seeing rainfall equal to half an average winter. So far this year, we are seeing nothing comparable.
This season feels very different. The storm track has been tending toward north to south instead of the more common west to east, and most of the season’s storms so far have either bypassed or just touched our region. This happened again just a few days ago when a Pacific storm slipped south along the coast, leaving us dry, and then caused rain in Southern California.
I am speaking here more intuitively than scientifically, but all this feels very much like a classic La Niña winter — dry and cool. But there are some real wild cards in all this. They have to do with the fact that historic weather may not be a very good guide to the patterns emerging around us. The reason is climate change.
What does this mean locally? The biggest unpredictability this winter results from the huge changes taking place in the Arctic. The amount of sea ice in the far north has plummeted in recent years, and the Arctic Ocean is warming quickly. As a result, unpredictable things are happening to weather across the northern hemisphere.
Last winter saw extremely cold air spill out of the Arctic and plunge deeply southward into the heart of the nation. Will that happen again this winter? Could one of these outbreaks invade California? This is what is so significant about this winter’s north-south storm track in the far west. It could bring very cold northern air our direction, a rare event in Central California.
In the meantime, I’m assuming personally that we’re headed into a relatively dry winter. We’re coming out of two above-average winters, so a dry winter should come as no surprise. And if I’m wrong, I’ll be pleasantly surprised. Personally, I like to see deep snow in the mountains and lots of spring runoff in the Kaweah River.
So let’s cross our fingers and hope that the weather gods decide to confound my expectations and send some major storms our way.
Three Rivers resident William Tweed writes about the natural world of Tulare County. His column, copyrighted and printed by permission, appears every other week in the Visalia Times-Delta.