Ag Weather Forum

Temperatures have been riding up and down like a rollercoaster recently and that sort of pattern is expected to continue through the rest of September.

Mild weather in mid-August was pleasant for a lot of areas of the country outside of the Deep South. But that was replaced by a stretch of hot and largely dry weather for the end of August. The hot conditions came to a close late last week with a strong cold front that brought scattered showers and a much milder period of weather for the first few days of September. A quick day or so of above-normal temperatures is spreading from the Plains into the Midwest, but another strong cold front will press through the rest of this week and temperatures are set to fall significantly again.

It will be the lowest temperatures since spring for a lot of areas this weekend. Temperature anomalies of 10 to 15 degrees below normal are forecast for the weekend. Low temperatures are forecast to be in the 40s across the Upper Midwest on Saturday, then the majority of the Corn Belt on Sunday. Additional cool weather may stick around in the Eastern Corn Belt on Monday morning as well. However, models rarely do a good job of nailing overnight temperatures when conditions are nearly perfect for radiational cooling or so anomalously cool for the season. Both seem to be the case for the event this weekend that might produce a lot more readings in the 30s than your local forecast may be showing.

The conditions for good radiational cooling, or the way that Earth emits heat into space, require clear skies and calm winds. Such conditions are usual underneath large high-pressure centers, like the one that is forecast to move into the Corn Belt this weekend. The areas right underneath the highest pressure have the best chance for both criteria to be met. The eastern Dakotas, Minnesota, and northwest Iowa are the prime location for Saturday morning, Sept. 7. Iowa and Missouri are underneath the highest pressure for Sunday morning, Sept. 8.

Another way to get temperatures to quickly fall overnight is with dry soil conditions. With a lot of the corn and soybean crops maturing in these areas, soils are drying out faster and pockets of dry surface soils have already shaped up. A front that will bring the cold air may produce some limited showers, but it will be spotty at best. Drier soil conditions could help that to cool the air as well. However, very little of the crop is actually labelled as mature according to this week's USDA NASS weekly Crop Progress report, and so that may be of little consequence.

But with cold air coming in and settling over the Central and Western Corn Belt, actual temperatures, especially those prone to being lower in pits and valleys, are likely to end up colder than forecast. The risk of frost is low, however it is not zero, and there are likely to be spots that end up dangerously close both mornings. Farther east though, temperatures are likely to stay in the 40s Fahrenheit. Residual cloud cover and even light winds will likely keep most areas comfortably above the freezing mark.

Then next week we see a rise in temperatures east of the Rockies yet again. Heat will build up in the West through the weekend and records are forecast to break over the next several days. That heat will slowly spread eastward through the country, being more pronounced over northern areas. Some areas that end up in the 30s F on Saturday morning may challenge the 90-degree mark by the end of next week. The Northern Plains and southern Canadian Prairies are likely to be hotter than most of Texas next week, a rare feat. The heat will be tough to get rid of but may be reduced toward the end of the month, and we may or may not be talking about another risk of a killing frost going into early October.

The rollercoaster ride will keep going, but the prospect for precipitation is going to be tough. This week's front will produce very little. And the heat next week will keep much of the country dry as well. When the temperature finally comes down later this month, it'll likely be due to a storm system moving through. The Northern Plains and Canadian Prairies look to have the best chances of rain, though, and not portions of the Corn Belt that are still behind a bit developmentally. How that will affect this season's good crop yield forecasts is still a bit of an unknown.

The heat will arrive next week just in time for Husker Harvest Days in Grand Island, Nebraska. If you'll be going, you can find me at the DTN booth on the east side of the grounds, booth 802. I'll likely be drinking a bottle of water or two as I give an update on the fall and winter weather outlook, and give a couple of hints about the start of next year. Come say "hi" and get out of the heat for a bit!

To find more weather conditions and your local forecast from DTN, head over to https://www.dtnpf.com/…

John Baranick can be reached at john.baranick@dtn.com

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