La Niña? … Is that you?

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JONATHAN P. THOMPSONDEC 6
 
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While most of the West remains in some stage of drought, the situation is markedly improved over a year ago—especially in parts of the Southwest—despite the La Niña phenomenon that tends to result in a warmer, drier weather in the southern part of the region. Source: U.S. Drought Monitor. 
Aridification Watch

The meteorological winter has only just begun, and the 2023 water year is a mere two months old, so it’s probably too early to be talking about snowpack and precipitation trends. But I’m going to do it anyway because things are getting kind of interesting. 

As I’ve noted before, La Niña has returned for a third consecutive winter, a rare occurrence. La Niña strengthens the trade winds along the equator, pushing warm Pacific Ocean water away from South America’s west coast, which then causes cool water to upswell to the surface to replace the warmer waters. This pushes the jet stream northward, 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 always followed the rules. What else is new, right? For example: 

  • The snowpack in the Upper Colorado River watershed is currently just above the median for this time of year, and is quite a bit healthier than on this date in 2021 and 2022—also La Niña years. If current trends continue through the winter it 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 apparently hammered southwestern New Mexico, as well, as streams and rivers there swelled up to levels usually only seen during summer thunderstorms. The Blue River in Clifton, Arizona, shot up from about 20 cubic feet per second to almost 3,500 cfs in a matter of hours, setting a new high for 2022. Also: Dave DuBois @NMClimateThe USGS stream gauge San Francisco River at Glenwood is currently at 3070 CFS. It peaked at 3780 CFS at 10:15am this morning. Past high flow was 280 CFS back in 1993. #nmwater #nmwx 10:56 PM ∙ Dec 5, 202214Likes5Retweets
  • Meanwhile, the Northwest is cool and wet, just as one would expect during a La Niña year. 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, for example, 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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