There comes a point during mid-summer when the veil of uncertainty lifts regarding the nature of the upcoming winter season and we are at that point now.
The key tool for seasonal forecasting in our region is the correlation between El Nino (warmer than normal water in the tropical Pacific) and La Nina (the opposite) and the large-scale weather circulation over our region. El Nino years tend to bring our region warm/drier conditions with a lower than normal snowpack. La Nina years tend to be cooler/wetter and are the periods skiers dream of.
Interestingly, there is a spring predictability barrier for such forecasts, with forecast skill increasingly greatly during the summer (see figure below and NOAA discussion of this effect). As you can see in the figure (which shows the skill in predicting El Nino/La Nina) by August, NOAA has almost achieved skill at the 80% level. Good enough to share with all of you on this blog!
Let’s begin by looking at what is happening right now, viewing the key sea surface temperatures in the central tropical Pacific (showing the difference from normal, known as the SST anomaly). The areas we use is called the Nino3.4 region.
Wow…a big change occurred in May, going from warmer than normal ( El Nino) to cooler than normal (La Nina) conditions.
Model forecasts for this winter are highly suggestive of strengthening of La Nina, which will continue into mid-winter.
As a result, the National Weather Service Climate Prediction Center (CPC) is now suggesting a better than 50% chance of La Nina and very little chance of El Nino this winter (see below).
But what about the best extended forecasts in the world? Those by the European Center? As expected during a La Nina year, it is going for a wetter than normal winter (Dec-Feb)–see below. Good for fish and water resources.
But what about temperature? In La Nina years, the strongest correlations with our weather occurs after January 1st, so let’s look at the temperature anomaly (again, difference from normal) for January (see below). Cooler than normal.
So what does wetter and cooler than normal suggest to you? Good snow accumulations in January.
Now I don’t know whether the ski areas will be operating in January due to COVID-19 (if people stay outdoors in the fresh air, it might be safe enough, as long as no indoor eating/drinking/congregation areas are open). But if they are open, this might be the year to take a chance on a season’s pass.
But no guarantees, of course. The El Nino/La Nina influence weights the “meteorological dice” but does not guarantee a perfect forecast of the upcoming winter’s weather.
via Watts Up With That?
August 8, 2020 at 08:22PM