Ag Weather Forum

Early autumn finds dryness and drought in place over a much greater portion of the primary crop areas in the United States compared to the end of the spring season. Back at the end of May, the U.S. Drought Monitor showed 26.45% of the contiguous U.S. in some phase of dryness or drought. But in early September, 65.31% of the contiguous U.S. had dryness or drought in effect according to the Drought Monitor -- an expansion of more than two times from the start of the three months of summer to the beginning of autumn in the meteorological calendar.

The NOAA National Centers for Environmental Information (NCEI) summary of U.S. precipitation for June-July-August noted that precipitation was above average in parts of the Upper Midwest, Northeast, Southeast, Gulf Coast and central Rockies. The Ohio Valley through the Gulf Coast along with the western U.S. and the Central and Southern Plains had below-normal precipitation. Summer dryness was especially harsh in the Ohio Valley, with West Virginia recording its fifth driest summer on record. Parts of the Ohio Valley went from zero drought at the start of summer to Exceptional Drought (D4) in early September.

Meanwhile, the Pacific Ocean Southern Oscillation Index (SOI) continues to point to La Nina development. The SOI 30-day average on Sept. 11, 2024, was +10.21, well above the La Nina threshold of +7.0. La Nina tends to support below-normal precipitation during the fall months in the interior U.S.

The next week brings the prospect of moderate to heavy rainfall to some drought-affected areas, notably the northern Rockies, Northern Plains and the Delta and Southeast. But such regions as the Central and Southern Plains and much of the Midwest may have anywhere from dry conditions to only light precipitation. That is a concern to University of Nebraska-Lincoln Extension Climatologist Eric Hunt. Hunt noted in a Sept. 10 webinar that these drier areas in many previous fall seasons when La Nina was developing have tended to miss out on moisture.

"For a lot of the Southern Plains, Central Plains and Western Corn Belt, we have tended to be drier than average some of these years like 1999, 2010, 2020 in particular were very dry across a lot of this region," Hunt said. "The historical recent past is not necessarily favoring widespread precipitation ... So, hence my concern for additional drought development across this region of the Corn Belt if we don't get that really robust rainfall this next week."

Drier conditions favor row-crop maturation, early harvest and winter wheat seeding. On the other hand, a lack of moisture is unfavorable for winter wheat and pasture soil moisture, livestock water ponds, and the U.S. interior river transportation system, which is already stressed by low water levels.

DTN Basis Analyst Mary Kennedy offered more details on river transportation issues here: "Lower Mississippi River Water Levels Falling Just as Fall Harvest Begins," https://www.dtnpf.com/…

DTN Meteorologist Teresa Wells outlined the potential for Hurricane Francine-related rainfall in the southeastern U.S. here: "Hurricane Francine to Make Landfall as Category 2 Hurricane,"

https://www.dtnpf.com/…

Bryce Anderson can be reached at bryce.anderson@dtn.com

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