Previous episodes coincided with historically dry periods
By Bob Berwyn
SUMMIT COUNTY — Based on experimental forecasting, odds are close to 40 percent that La Niña will return for a third winter, according to Boulder-based NOAA climate scientist Klaus Wolter, who emphasized that’s not the official outlook from NOAA or the Climate Prediction Center.
A triple La Niña could spell trouble for an already dry Colorado, as three-year La Niña events are statistically linked with some the driest conditions on record in Colorado, including a historic mid-1950s drought, the mid-1970s drought that prompted ski resorts to start making snow, as well as the drought in the early 2000s that culminated with the ultra-dry year of 2002, when Dillon Reservoir nearly disappeared in a cloud of dust.
The best hope for a moisture turn-around would be a sudden switch to El Niño, which some climate models are predicting, but Wolter calculates that there’s only a 20 percent chance of that happening.
La Niña and El Niño are part of a cyclical shift in sea surface temperatures — and related wind patterns — in the equatorial Pacific Ocean. Under a La Niñ regime, cooler-than average ocean temps are found across the eastern Pacific, often driving changes in the storm track that bring wetter-than-average conditions to the Pacific Northwest, as well as to northwestern Colorado.
El Niño often drives big storms straight into the coast of California, making for wetter-than-average conditions in southern California and across the desert Southwest.
Based on records going back about 100 years, there have been 10 “double-dip” La Niñas, four of which continued on to a third year, while six switched to El Niño conditions. None of the douple-dip La Niñas ended up in so-called ENSO-neutral conditions.
Wolter explained via email:
“The four ‘triple-delight’ Las Niñas were from 1908-11 (drought in much Western U.S., includes the dry March of 1910), 1954-57 (big drought of record until late 1990s; includes the dry Marches of 1955 and ’56), 1973-76 (that was our lucky break where the drought waited until 1976-77 to hit our state), and 1998-2001 (main drought hit from late 1999 through most of 2002, offset by one year from original La Niña.
“There seems to be a common thread here that drought conditions sometimes kick in one year after the La Niña forcing sets up),” Wolter wrote.
“I am personally leaning a bit harder on the odds for a third La Niña winter. We basically have another two months or so where the system could tip over to El Niño (which is often much wetter during spring if El Niño rushes in), so this one bears watching … ” he concluded.