By Ben Trefry
Oct 01, 2017
After a record-breaking winter that was initially supposed to be dry, weather forecasters are being more cautious with this year’s long-range forecast. Although the winter of 2017-2018 was forecasted to be a moderate El Niño this spring, things have since shifted and the jury is out.
According to Jon Gottschalck of the Climate Prediction Center, part of the National Weather Service, the odds of a weak La Niña (the same pattern that was present the beginning of last winter) have increased considerably since this spring. Based on below-average surface and subsurface temperatures in the equatorial Pacific, it is now the most likely pattern. “Some [forecasting models] indicate conditions for the winter to be borderline La Niña during the Dec-Jan-Feb three month winter season,” says Gottschalk.
However, the La Niña/El Niño cycle is only one of many factors that influence our weather. Gottschalk says that, despite the weak La Niña pattern present last winter, the precipitation forecast for the Eastern Sierra was actually neutral. He also criticized the forecasting that, last summer and fall, wrote off our record year as a dry La Niña winter. “The forecast was certainly not good and would be described in our business as having low or no skill,” Gottschalk told The Tiger Tribune. El Niño is seen as good for precipitation and La Niña as indicating a dry winter, but the truth is that, no matter which of the patterns is in place, precipitation could go either way.
The cycle that drives La Niña and El Niño, El Niño-Southern Oscillation or ENSO, especially when weak, is only a reliable indicator of below-average precipitation in Southern California. It is often neutral for the Eastern Sierra. According to a climate chart by the National Weather Service, a strong El Niño, on average, only adds about 3 extra inches to Mono County’s precipitation – which on its own does not make a big winter, although most of the big winters that locals remember were during El Niño years. (A weak El Niño adds about 2 inches.) The results for La Niña were still more ambiguous – the chart showed that even a strong La Niña had no impact whatsoever on Mono County precipitation.
Howard Scheckter, our local weather forecaster who broadcasts on KMMT Radio, says that the beginning of last winter was a weak La Niña, but the pattern shifted to neutral for most of the winter. Scheckter predicts a wet November and December with cold or average temperatures for this winter, then a dryer-than-average January and February.
Meanwhile, the Climate Prediction Center has taken a much more conservative outlook. According to Gottschalk, the winter will likely feature consistently above-average temperatures, but there is no outlook for precipitation. “The uncertainty in some of the forecast information we have available is very high so for precipitation we do not have a clear, reliable climate signal for your area,” he told The Tiger Tribune. “In other words, equal odds [for above– below–, or average precipitation].”
It’s important to understand that, just because the same pattern (weak La Niña) that happened last winter is likely, does not mean that the upcoming winter will be a repeat. There are lesser-known cycles similar to the ENSO that also influence our weather, such as the Quasi Biennial Oscillation, which controls the Hudson Bay Low. Sunspot cycles are also thought to have some effect on weather patterns, though it’s unclear how much, or if at all, the Eastern Sierra and California as a whole are affected.
There are other factors as well, so the oñnly reasonable prediction we can make is that temperatures will likely be above average throughout the course of the whole winter, owing to climate change and other trends. La Niña is associated with below-normal temperatures, but a weak La Niña will not likely have much effect. However, this far out, pretty much anything could change.