Impacts on Colorado uncertain
By Bob Berwyn
SUMMIT COUNTY — A classic El Niño may be developing across the eastern Pacific, with warmer-than-average water temperatures starting to spread westward from the coast of South America, according to NOAA’s Climate Prediction Center.
For the month of June, the pattern of sea surface temperatures overall remained in a neutral phase, but with growing positive (warmer than average) equatorial Pacific sea surface temperature anomalies, NOAA has issued an El Niño watch, reflecting a likely emergence of of El Niño in the late summer or fall.
Ocean-wide, the warming off the coast of South America is consistent with patterns associated with the development of previous El Niños, including a weakening of low-level trade winds across the east-central equatorial Pacific. Those winds, blowing east to west, normally push the warmer waters to the west. Another sign is the weakening of the persistent pattern of enhanced convection near Papua New Guinea.
The pattern was named by fishermen on the west coast of South America, who observed the changes in the ocean around Christmas. The warmer water has less nutrients and impacts the fishery in the region. It can also lead to heavy precipitation in Peru.
But development of a full-fledged El Niño is far from a sure thing. Dynamic climate models, based on real-time data and observations, suggest the development of El Niño during the July to September period.
But statistical models are predicting neutral conditions through the remainder of the year. In the El Niño watch, NOAA said forecasters are leaning toward the dynamical models because of the strengthening of observed signals.
Strong El Niños have a global effect, shifting areas of temperature and precipitation. For example, the California coast sees some of its biggest winter storms during El Niños, and the southwestern U.S. can also see above-average precipitation. Often, eastern Australia is dry and warm.
El Niño can also lead to wet and cold conditions across the south-central and southeastern U.S., as well as warmer-than-average conditions in the Gulf of Alaska and the northeast.
The impacts in Colorado are less clear and can be difficult to forecast. In some years, the emergence of El Niño has resulted in wet weather during the late summer and autumn, but that pattern doesn’t always continued into the winter.
Southwestern Colorado can experience big winters during an El Niño, but the rest of the state’s mountains can go either way. There have been some big El Niño snow years in the central and northern mountains, but there have also been some very dry winters.
About 10 years ago, a three-year La Niña phase (1999 to 2001) shifted to an El Niño about halfway through 2002, leading to one of the driest winters on record.
The most recent El Niño phase in Colorado started in mid-summer 2009 and lasted through the spring of 2010, bringing near-average precipitation that winter. Another strong El Niño in 1997-1998 brought good snows to Colorado.