La Nina to Keep WCB Dry

The Pacific Ocean cool-water La Nina event continues to grab the ag weather news headlines in mid-November. An updated La Nina Advisory from the NOAA Climate Prediction Center (CPC) has some thought-provoking details about the 2020 La Nina event.



The central and eastern equatorial Pacific Ocean has an average temperature of 1.3 degrees Celsius (2.3 degrees Fahrenheit) below normal. The CPC calls this La Nina event the eight-strongest dating back to 1950. Climate forecast agencies now call for a 95% chance of La Nina continuing through the upcoming winter into the spring of 2021; in addition, there is almost a two-thirds probability -- 65% -- of La Nina lasting through the 2021 spring.


During a conference call Nov. 19, Iowa State Climatologist Justin Glisan said that the likely presence of La Nina brings a wide variance in the weather pattern forecast indications across the central U.S. with what Glisan called a "classic" La Nina effect.


That effect includes above-normal precipitation during the rest of calendar year 2020 and the first quarter of 2021 over the northwestern U.S. and in the eastern Midwest. In the western Midwest and all but the northern one-third of the Plains, the forecast has below-normal precipitation. That drier trend in the western Midwest and most of the Plains means that drought areas have a high probability of continuing on that track through spring.


There is also the question of how much the dry fall pattern will affect the 2021 row crop season. The potential is worth thinking about. "The drier-than-normal conditions mean you don't have a lot to work with (on soil moisture)," said Glisan. "This dryness impact could feed on itself."


USDA Midwest Climate Hub Director Dennis Todey noted that severity of dryness is important. "Moderate dryness is not a huge issue," Todey said. "But we see that Northwest Iowa has only 2 to 3 inches of moisture in the 5-foot profile compared with 10 to 12 inches of moisture for a full profile. That is a big decline on supply."

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