The potential for a La Nina weather pattern this winter is looking more and more likely. The latest forecast says there’s a 66 percent chance for La Nina, a figure that’s been steadily rising for the last few months.
That’s according to Brian Brettschneider, with our Ask a Climatologist segment.
He said La Nina typically brings cooler and drier conditions to Alaska. And because of global warming, that may mean a more typical winter.
Brian: Since we’re comparing against the 1981 to 2010 climate normal period, we’re already a couple of degrees warmer than that. So we’re starting off, all things being equal, as being pretty far above normal. La Nina, and it’s not a done deal, generally it’s going to tilt us toward cooler temperatures. So more than likely it’s going to send us back a couple of degrees, which would put us close to the normal range.
Annie: We had a La Nina last winter. How unusual is it to have back-to-back La Nina’s?
Brian: It is unusual, but it’s not unprecedented. It’s not one La Nina- we had a La Nina last winter and it faded away, but now we’re transitioning back into a new La Nina, so they are separate events. Again, it’s not unprecedented, but it is pretty uncommon. Normally, they’re going to be spaced a couple years apart.
Annie: Do we know why we would have two in a row?
Brian: Actually, we don’t. With El Nino’s and La Nina’s, we kind of understand how they work, but we don’t have a good understanding of what initiates them or why they occur. So that’s an area of intense research. But for now, we watch the progression of it and don’t understand why they occur.
Annie: How does the La Nina work and why does it bring drier, cooler weather to Alaska?
Brian: El Ninos and La Nina’s- they’re a measure of what the ocean temperatures are in an area of the central tropical Pacific Ocean within five degrees of the equator. And it’s curious as to how that affects things in Alaska. The reason it does is because it’s where these warm pools of water set up. In El Nino, they set up more towards South America. In La Nina years, they set up much more towards the west, say towards Indonesia. So you have these tropical thunderstorms sending heat, air movement, masses of air, and that affects large scale atmospheric patterns, called Walker Cells. And it also influences which direction the wind is coming from at upper levels. So in that La Nina year where the warm pool is set up to the west, and that’s where the tropical storms are, we end up with a kind of northerly flow across Alaska which drags in colder air from farther to the north and limits the amount of moisture that comes in.