El Niño is running late-oh.
The climatological pattern that could contribute to a wetter-than-average winter in Colorado is taking its time becoming an actual thing this season. But the National Oceanic and Atmospheric Administration is still expecting its arrival, hoping that it could help alleviate drought conditions that are particularly severe in the Four Corners region.
That region has been especially dry in recent years, and currently is experiencing the worst drought conditions in the continental United States. It's ranked as being in exceptional drought, the worst category, with that drought level extending north through Delta and eastern Montrose counties, even crossing into a bit of eastern Mesa County. The rest of Mesa County and the rest of western Colorado are all in lesser stages of drought, with conditions having eased thanks to some fall moisture.
While southwest Colorado also benefited from that moisture, conditions more recently have been drier there. The Natural Resources Conservation Service reported as of Thursday that while statewide snowpack averaged 117 percent of normal, southwest Colorado has fallen below median snowpack, with the Gunnison River Basin at 94 percent, the Upper Rio Grande at 86 percent and the Four Corners basins at just 70 percent. That compares to 133 percent for the Upper Colorado River Basin, 130 percent for the Yampa/White river basins, and around 150 percent for the Arkansas and South Platte basins.
An El Niño pattern could improve the state's fortunes, particularly in southern Colorado. Mike Halpert, deputy director of NOAA's Climate Prediction Center, said in a webinar this week that an El Niño watch has been in place since the June-July timeframe, which is a long time to be in watch status. He said forecasters had expected an El Niño to become active by now.
"We still think it will form," he said.
In fact, the Climate Prediction Center thinks there's an 80 percent chance of what likely will be a weak El Niño forming this winter, and a 50 to 60 percent chance of it carrying over into spring. He said El Niños typically last nine to 12 months.
El Niños are associated with warmer surface-water temperatures in the eastern equatorial Pacific Ocean. They tend to impact the jet stream over the United States, bringing wetter weather to the southern United States, including the Southwest.
While the warmer eastern Pacific surface-water conditions exist, Halpert said it takes more than that for the El Niño to set up.
"Those changes in the ocean need to have the atmosphere responding to those changes," he said.
Specifically, the ocean warming needs to alter tropical rainfall patterns, bringing more rain to the central and eastern Pacific and less rain over Indonesia, and it's that rainfall shift that affects the jet stream and moisture patterns in the United States.
Halpert said he's expecting such an atmospheric response to happen shortly. Fortunately, he said, in the meantime the short-term forecast over the next few weeks already is for wetter-than-normal conditions. That means a likely wetter-than-average start to winter in the Southwest even before El Niño influences kick in.
Based in good part on that El Niño forecast, the Climate Prediction Center says there are above-average chances for above-normal precipitation in Colorado through March.
That could be particularly important in southwest Colorado and the Four Corners area. The drought is taking its toll on streamflows, municipal water suppliers in the Four Corners area, and hay and cattle production, said Royce Fontenot, senior service hydrologist for NOAA and the National Weather Service in Albuquerque, New Mexico.
Blue Mesa Reservoir is continuing to serve as a stark indicator of area drought conditions. The reservoir's water levels were at 43 percent of average for this time of year as of mid-month, and it's just 30 percent full. Statewide, reservoir storage is at 81 percent of average for this time of year.
Underscoring just how dry things are, Fontenot said that according to one drought index, it would take 167 percent or more of normal precipitation over the next six months to end the drought in the Four Corners area.
"Essentially you need all you normally would get plus 60 percent more," he said.
John Berggren, a water policy analyst with the Western Resource Advocates conservation group, said even an average snowpack year would be great for southwest Colorado, but the fact that it wouldn't be enough to end the drought there shows just how bad conditions are.
"The current drought that the Four Corners is in is just that significant," he said.
While this year's El Niño isn't expected to be strong, Halpert said there are no guarantees based on the strength of an El Niño. The 2015-16 El Niño was one of the three strongest in the last half-century, but didn't result in the typical additional moisture impacts of such a powerful El Niño, he said.
It's also noteworthy that the Climate Prediction Center says there is an above-average chance of warmer-than-normal temperatures this winter in Colorado. Halpert said El Niños used to be associated with colder winters in the southern United States, but in light of a warming climate over the years, forecasters aren't expecting below-average temperatures this year.
Fontenot said the trend of warming temperatures matters when it comes to drought assessment, when taken in context with other factors such as the region and time of year, which can affect things such as levels of evaporation, and of water absorption and release by plants.
"Particularly here in the Southwest it's becoming much more of a factor in looking at how we assess drought," he said of the warming pattern.
Berggren said that even with an above-average snowpack season, if there is a warm winter and spring, "you can very quickly eliminate those gains … which is unfortunate."
He said even a weak El Niño is better than no El Niño when it comes to precipitation, particularly in the Four Corners area. That said, "it's not going to be a gangbusters of a winter, especially with the warmer-than-average temperatures that are expected," he said.