Ag Weather Forum

Much of the Corn Belt has been spoiled with above-average temperatures this fall. Temperatures for the months of September and October reached an average of 4-8 degrees Fahrenheit above-average across portions of the Upper Midwest and Northern Plains. However, meteorological winter is fast approaching. Meteorologists define meteorological winter as the months of December, January and February. DTN's forecast is hinting that temperatures may feel more winter-like by the end of the month into early December across the north-central United States.

During this time of year, it is not uncommon to see models disagree as the polar jet stream and subtropical jet stream adjust their location across North America. The polar jet stream typically lingers farther north in Canada during the summer months, while the subtropical jet stream hovers across the southern half of the U.S. As we transition into winter, the polar jet stream starts to dip south into the northern U.S. This transition can create a more active weather pattern, and model guidance can struggle to agree on how to resolve the evolution of storm systems.

Even though model guidance can have disagreements during this time of year, it is worth noting that long-range weather models are showing a fair amount of agreement on a stretch of cold weather arriving for the north-central U.S. during the last week in November. Both the American GFS and European models show below-average temperatures from the Canadian Prairies expanding into the Northern Plains and Upper Midwest. While they both show this cold signal, they disagree on the magnitude and timing of the colder temperatures.

When there are disagreements among models, it certainly makes my job harder as a meteorologist, but this is when I will turn to model ensembles. Model ensembles offer a range of possible outcomes on the weather. With the impending cold snap at the end of November, the GFS ensemble is favoring temperatures 6-16 degrees F below average in the Dakotas. The European ensemble favors temperatures 4-12 degrees F below average. These magnitudes of below-average temperatures translate to low temperatures approaching the single digits above zero across North Dakota.

Outside of the Dakotas, parts of Minnesota, Iowa and Nebraska could see temperatures dip to 4-8 degrees F below average from the end of November into early December. This would lead to low temperatures bottoming out in the middle teens to lower 20s.

As we head into the winter months, snowfall can have a large impact on temperatures. Earlier this week, northeast South Dakota, eastern North Dakota and northwest Minnesota saw 2 to 4 inches of snow as a storm system moved through and brought blizzard conditions for north-central North Dakota. The weather pattern could remain active over the next 10 days for the central U.S., so any additional snowfall across northern areas could keep temperatures on the cooler side.

The flip between above-average temperatures and drier conditions to sub-freezing temperatures, and snowfall could have implications on the winter wheat crop across the Northern Plains. USDA's latest crop progress report released Monday, Nov. 18, shows South Dakota has 83% of its winter wheat crop emerged. Additionally, 43% of the crop is rated in fair condition while only 4% is rated as excellent. Much of South Dakota has moderate-to-extreme drought as well, which may be a contributing factor to the lower percentage of the winter wheat crop that is rated as excellent.

Winter injury on wheat can be more severe when soil is dry, especially if the crop hasn't had the proper amount of time to cold-harden. According to Kansas State University, wheat has very few secondary roots and no tillers, it may be more susceptible to winterkill if soil is dry. Drier soil will also warm up and cool down at a faster rate than moist soil. As the north-central U.S. braces for the first blast of arctic air next week, places that still have emerging winter wheat could be at risk for winterkill. (https://eupdate.agronomy.ksu.edu/…)

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Teresa Wells can be reached at teresa.wells@dtn.com

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