La Niña conditions drive above average temperatures and below average precipitation in areas
The expectation La Niña conditions will persist throughout the coming winter is the number one driver for The Weather Company’s current weather outlook, which predicts mild and above average temperatures across the U.S. through the next few months.
“Mild temperatures could dominate a large part of the U.S. this winter, especially in the South and East,” states The Weather Company. “Above average temperatures are expected in most locations from the southern and eastern states to the West Coast. Areas from the Southern Plains to the Southeast and Northeast could have temperatures way above average, while parts of Montana and North Dakota are the only areas where somewhat colder average temperatures are expected.”
According to the National Weather Service’s National Oceanic Atmospheric Administration (NOAA), La Niña refers to the periodic cooling of ocean surface temperatures in the central and east central equatorial Pacific and may occur every three to five years.
During a La Niña event, the changes in Pacific Ocean temperatures affect the patterns of tropical rainfall from Indonesia to the west coast of South America. These changes affect weather patterns around the world, and the effects are usually strongest during the winter months when the jet stream is most powerful over the U.S., explains NOAA.
“From a historical perspective, the increasingly strong La Niña event would force an exceedingly warm winter and early spring, with colder air across western Canada and parts of the northwestern and north central U.S.,” says Todd Crawford, chief meteorologist at The Weather Company.
While warm La Niña Novembers tend to be followed by similarly mild winter conditions, Crawford notes the U.S. will see quite a few temperature fluctuations, which may differ from the expected overall trend.
According to NOAA, areas from the Midwest to the West Coast are expected to see near-normal temperatures during the month of December.
The highest chance of above average temperatures is in the South and East, while below average temperatures are likely to be seen in Montana into the Northern Plains.
January is typically the coldest month of the year for many parts of the U.S., but NOAA says this may not be the case this winter. The service notes a widespread area from the Plains to the East Coast is expected to see temperatures way above the average, while somewhat colder than average temperatures are forecast for a small part of the Northwest.
NOAA forecasts February temperatures to be similar to January, with way above average temperatures from the Central and Southern Plains to the East Coast.
Snowfall and snowpack
While snowfall is hard to predict, Dr. Stephen Baxter, meteorologist with NOAA’s Climate Prediction Center notes there are some general themes when it comes to La Niña’s influence on snowfall.
“Generally, La Niña favors increased snowfall over the Northwest and northern Rockies, as well as in the upper Midwest Great Lakes region and less snow in the Central and Southern Plains, Southwest and mid-Atlantic,” Baxter explains.
Below nine percent of the Lower 48 states were covered by snow on Nov. 22, according to NOAA, which noted this is the least amount of snow cover on this date since 2012, when just over six percent of the contiguous U.S. was covered by snow. Last year at this time, over 20 percent of the Lower 48 was snow covered, according to NOAA.
For nearly all major basins in Wyoming, early water year snowpack and snow water equivalent (SWEs) were below average at 50 to 75 percent of the median. The highest SWEs of 125 to 150 percent of the median were over the Upper Yellowstone and Shoshone Basins in northwest Wyoming.
Generally, according to NOAA, Wyoming saw below average precipitation totals during the early part of water year 2021, which spanned from Oct. 1 to Nov. 24, 2020.
With this said, precipitation would be happily welcomed. According to The Weather Company, drought expanded and worsened across most of the West during the summer and early fall.
In fact, more than 85 percent of the West is currently abnormally dry, at least, with over three-quarters of the region in moderate to severe drought.
On Nov. 17, NOAA reported nearly 45 percent of the U.S. cattle industry, 36 percent of U.S. hay acreage and 49 percent of the nation’s alfalfa acreage was experiencing drought conditions.
Severe to exceptional hydrologic drought conditions have also been reported across central and south central Wyoming.
Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to firstname.lastname@example.org.