Weather Patterns Dominated by La Nina, but Not for Long
If you have been paying attention to the long-range weather forecasts over the last couple of years, the words “La Nina” have been plastered across your screen almost constantly since the summer of 2020. La Nina is the cold side of the El Nino Southern Oscillation (ENSO), which partly describes sea-surface waters in the tropical Pacific Ocean compared to normal. La Nina means that water temperatures are colder than the historical average. This effect has been in control of the weather patterns across much of the globe for the last two Northern Hemisphere winters and is headed toward a third.
Typically, La Nina brings about large disruptions in the Polar Vortex or the jetstream that circles around the North Pole. During the winter, such disruptions usually lead to a large ridge of high pressure over Alaska and a trough over eastern North America in the upper levels of the atmosphere. Flowing from high to low, this transports cold air from the Arctic south through Canada and into the North-Central U.S. by the way of clipper systems.
These clipper systems usually do not have a lot of moisture associated with them for the Northern Plains, but do lead to bands of light snow. La Nina’s frequent clipper pattern over the winter is likely lead to near-normal precipitation amounts and snowpack across South Dakota, though of course, there will be variability at the local level. Cold air that follows the clippers should have a stronger influence on the average temperatures this winter than any warmth that comes ahead of these systems or when the systems go dormant from time to time as they often do.
Near-normal snowpack in the winter alone will not be able to ease drought conditions that have been growing over the fall season, a typical feature of La Nina. However, La Nina conditions are forecast to turn to a neutral state in the spring by all major climate models around the world. Long-range forecasts have it instead flipping to El Nino sometime during the summer or fall of 2023.
You may have gotten sick of the summertime heat and frequent drought conditions, but we could see a big change in the weather for the next growing season. Confidence in any long-range forecasts you see for spring or summer should be pretty low at this point in the year. But anything like the last two summers of hot and dry conditions are not likely to repeat themselves next year, and that could mean better growing conditions. Though soils may be dry to start the year, and getting better subsoil moisture will be left to the spring, less heat and near-normal rainfall patterns are the most likely scenario for the summer. However, there is a lot of variability in years without a strong driver in the Pacific Ocean. If El Nino does not develop this summer, conditions could be very hard to predict more than a few weeks out.
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By: John Baranick
DTN Ag Meteorologist