Pacific Ocean waters hold key to snow year
Boy or girl?
A huge area of the Pacific Ocean west of Ecuador to roughly the International Date Line can influence weather patterns across North America with either warmer- or cooler-than-average temperatures. Those patterns are called “el Nino” — the boy — and “la Nina” — girl. But which is which?
• El Nino patterns stem from warmer-than-average water temperatures.
• La Nina patterns reflect cooler-than-average temperatures.
Those shifts are a matter of just a degree or two, but can have a significant effect on winter weather in the western U.S.
EAGLE COUNTY — Long-range weather prediction is still an inexact science based on both current patterns and history. Those predictions get more tricky when historical anomalies enter the mix. That’s the case for the coming fall and winter.
Meteorologists have long known about El Nino patterns in the Pacific Ocean west of Ecuador. An El Nino pattern will develop every few years. When it does, it affects weather over much of North America. This year’s El Nino is shaping up to be a big one — the biggest ever measured, in fact, with temperatures more than 2 degrees Celsius above average.
According to a report posted on OpenSnow.com, meteorologist Joel Gratz wrote that the significance of that change is the effect on where thunderstorms form in that part of the ocean. That “changes weather patterns across the globe,” he wrote.
Each El Nino year is different, of course, and, again, long-range predictions can be tricky things. But there are patterns. In an OpenSnow summary of the possible effects on winter weather, the map shows that the central and northern Colorado Rockies should have roughly average snowfall.
But the changes can be more significant than just average snowfall.
According to a recent report by the national Climate Prediction Center, forecasters are calling for above-average precipitation for much of Colorado for September, October and November, with the highest probability for above-average rain and snowfall in the Four Corners area.
At the National Weather Service office in Grand Junction, meteorologist Joe Ramey has worked to pinpoint those forecasts to specific areas. For the Vail area, Ramey’s analysis shows a “statistically significant” chance for a wet fall.
EL NINO WINTERS
Ramey said El Nino patterns typically result in above-average precipitation in the fall and early winter, then again in the early spring. But the heart of the winter months usually brings drier than normal precipitation.
“The bumps in the spring and fall are bigger, and the dips in the winter are deeper,” Ramey said.
Traditionally, El Nino winters tend to bring storms from the southwest, while La Nina winters — with cooler than normal temperatures in that area of the Pacific — generally bring more storms from the northwest.
That means El Nino years generally bring abundant snowfall to Wolf Creek Pass and other areas in southern Colorado, while La Nina years have greater impact on the mountains roughly north of Interstate 70.
This year’s pattern promises a mixed bag of relief for the drought parched West Coast. While Southern California is expected to benefit from winter storm patterns, the Climate Prediction Center is forecasting below-average precipitation for Oregon and Washington. That’s bad news for crews fighting large wildfires in that part of the country.
Those states, and perhaps the Vail Valley, would be better served by a La Nina pattern this winter. Looking back at the two biggest El Nino years, the pattern of 1986-87 was followed by a La Nina year that brought bunches of snow to the area. Local legend has it that the valley received more than 70 consecutive days of snow in the winter of 1987-88.
Still, coastal areas tend to be the more reliable recipients of the Nino/Nina weather patterns, Ramey said. The rest of the country is more hit and miss.
Ramey likened the Western U.S. to a “highway” for weather. A Nino or Nina pattern will put a “groove” in that highway, he said. But that groove isn’t a rail and is no guarantee of just where storm systems may go once they head inland. In fact, the Nina/Nino patterns affect only between 15 and 25 percent of storm systems moving into the continent. At least those patterns can be forecast to some degree. A year with average ocean temperatures means storms will head just about anywhere.
That could still be the case this coming winter. Remember, long-range predictions are tricky at best.
“I think I’ll finalize my winter forecast in about May,” Ramey said.
Vail Daily Business Editor Scott Miller can be reached at 970-748-2930, email@example.com or @scottnmiller.