La Ninas bring the cold, snow

Marked by colder than normal waters off of the coast of South America, La Nina is a climate phenomenon with wide-reaching effects. In the Upper Midwest, it has typically fueled jet stream patterns producing mild weather in the fall, followed by cold and snowy winters.

Three consecutive La Nina-impacted winters is a climate rarity, having occurred only twice in the past five decades. However, the precise effects of La Nina on Minnesota winters are mixed, with some experiencing only mild impacts and others outright defying the general trend.

The 2020-21 winter season saw above-average temperatures overall, although February was marked by a blast of harsh arctic air that produced extreme cold for several weeks. Last year’s winter was colder, though temperatures lingered above average into December.

What constitutes an average Minnesota winter has also shifted, with Minnesota winter temperatures warming by about 5 to 6 degrees over the last 50 years. Snowfall totals have also been on the rise, with much of that increased precipitation concentrated in large events.

While last winter may have been notably cold compared to the last 30 years, it didn’t approach the winters of Minnesota lore. Despite a harsh cold snap in December, this winter doesn’t seem on pace to be especially cold either, but it could be a different story in terms of snowfall.

For the Twin Cities, last week’s snow storm produced the 14th largest snowfall totals in recorded history. Season snowfall totals are now close to historic highs, within shouting distance of the 1991-92 winter season marked by the infamous Halloween Blizzard.

Tom Hoverstad, a scientist at the University of Minnesota’s Southern Research and Outreach Center in Waseca, said that the heavy snowfall represents a marked contrast with conditions in the fall, when the region saw a persistent and worrisome drought.

“In September and October we saw very little precipitation, about 6.5 inches short of our averages,” he said. “As of this point, we’ve already had more snow than we had all of last winter.”

For local farmers hoping to see their soil regain some moisture, the benefit will be limited, since frozen soil is impervious to water penetration. However, milder temperatures are nudging soil temps up, which could help to increase water retention in the spring.

Despite recent droughts, the overall trend over the last several decades has been toward increased moisture. Hoverstad noted that adapting to those changing moisture patterns is often more challenging for agriculture than adjusting to rising temps.

“If the climate warms a couple degrees we barely notice it because we have such swings in temperature,” he said. “Wetter conditions make a difference on crop farms for the long term — that’s a concern.”

Just how much farmers will benefit from the increased snowfall will depend in part on how it melts and what types of precipitation are received as winter turns to spring. Of course, a late and wet spring always has the potential to ruin farm yields.

Rice County Farmers Union President Steven Read said there are proactive steps that farmers can take to make the most of winter weather conditions. In particular, planting cover crops can reduce the risk of heavy winds blowing away precious topsoil in the absence of major snow.

“A few weeks ago if you were driving around the county you saw a lot of really bare black fields. That’s not good for soil erosion,” Read said. “When you have wind, you see a lot of soil from those uncovered fields being put into the ditches or environment.”

Significant snow cover not only mitigates the risk of wind erosion but also limits soil frost depth, helping the soil to absorb at least some moisture and allowing for the survival of crucial soil microbes that enhance the richness of local soil.

Yet while the trend has been toward receiving increased precipitation, it has often come in the form of major storms bracketing extended droughts. That’s far from ideal for local farmers, especially as large quantities of precipitation often run off of the soil rather than being absorbed.

“We’ll have to get used to when it rains it rains a lot and then it doesn’t rain for awhile,” Read said. “Everyone would like to have a little bit of rain frequently with a lot of sunshine and warmth, but we’re not seeing that.”

As part of the University of Minnesota Extension Service’s Let’s Talk Crops, a now annual online webinar series designed to provide vital information and insight for farmers across the state, Minnesota Department of Natural Resources Assistant Climatologist Pete Boulay will discuss the upcoming year’s weather forecasts.

In putting together his presentation, Boulay has leaned heavily on National Weather Service’s Climate Prediction Center projections. While long-range weather forecasting is always marked with plenty of uncertainty, NOAA’s projections utilize the full range of statistics at its disposal.

While the Climate Projection Center’s forecast of a warmer than normal January seems to be coming true, the winter storm last week is likely to deliver at least somewhat higher than anticipated snowfall totals for the month, barring a dry next several weeks.

Whether the wet conditions will continue into the rest of the winter is an open question. While La Nina-influenced winters have traditionally delivered more cold and precipitation later in the season, Boulay said that this winter has already defied that trend with a robust start.

“So far, it’s been just the opposite of what you’d expect from a La Nina winter,” he said. “It will be interesting to see how the rest of the winter goes.”