La Niña lite?
The little girl throws a few curveballs this time

La Niña lite?
Jonathan Thompson - 12/15/2022

While most of the West remains in some stage of drought, the situation has markedly improved over a year ago – especially in parts of the Southwest. This is despite a persistent La Niña pattern, which tends to result in warmer, drier weather in the southern part of the region. 

With the official start to winter still a week away and the 2023 water year a mere two months old, it’s probably too early to talk about snowpack and precipitation trends. But I’m going to do it anyway because things are getting kind of interesting.

La Niña has returned for a third consecutive winter, a rare occurrence. The cold-water phenomenon strengthens the trade winds along the equator, pushing warm Pacific water away from South America’s west coast, which causes cool water to swell in and replace it. This pushes the jet stream northward, typically bringing drier conditions to the Southwest and moisture and cold to the Northwest. At least that’s what usually happens.

So far, though, Western weather hasn’t followed the rules (what else is new, right?). For example, snowpack in the Upper Colorado River watershed is currently 116% of median for this time of year – quite a bit healthier than on this date in 2021 and 2022, also La Niña years. Likewise, the San Juan/Animas/Dolores/San Miguel basin was holding strong at 100% of median as of Dec. 13, thanks to an early-week storm. If current trends continue, they should buoy levels at Lake Powell or at least keep them from declining so rapidly. Currently, the reservoir’s surface is at about 3,527 feet above sea level. On the one hand, that’s 14 feet below what it was at this time last year, which is not so great. On the other hand, levels have held fairly steady since late September thanks in part to a wet fall.

Southern Arizona experienced its 16th driest November on record, which fits the La Niña pattern. But it was also the coolest November since 2004, in defiance of the pattern. Go figure.

As if to rub it in, Phoenix, which had a pretty healthy monsoon this summer, just experienced its wettest day in almost a year, receiving .76 inches of rain over a 24-hour period. Tucson, meanwhile, received .69 inches of rain during the first week of December, nearly five times the normal amount for the entire month.

The rains hammered southwestern New Mexico, as well, with streams and rivers there swelling to levels usually only seen during summer thunderstorms. The Blue River in Clifton, Ariz., shot up from 20 cubic feet per second to almost 3,500 cfs in a matter of hours, setting a new high for 2022.

Meanwhile, the Northwest is cool and wet, just as one would expect during a La Niña. A scan of SNOTEL stations in Idaho, Wyoming and Montana show some stations have more than twice the usual snowpack for this time of year.

Still, the winter is young, and things could change radically. Last winter started out dry in much of Colorado, leading to the late December Marshall Fire near Boulder that wiped out 1,000 homes. Then some monster storms came, forcing everyone to reassess. Then the dryness returned. This year, forecasters are expecting La Niña to mellow or disappear by early spring, so maybe things will return to normal. Whatever that means.

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