Corn Belt Weather Patterns Put Projected Yield at Risk - UNL CropWatch, July 8, 2011

Corn Belt Weather Patterns Put Projected Yield at Risk - UNL CropWatch, July 8, 2011

July 8, 2011

As we enter the heart of summer, it is time to review the cropping situation across the U.S. with an emphasis on the corn crop. Serious flooding issues remain across the northern Plains, while drought continues unabated across the southern Plains. In addition, recent dryness across portions of the central and eastern Corn Belt has producers on edge heading into the critical pollination period.

 14 day precip map

 Percent of normal precipitation for the period from June 23 to July 6. 
 (All maps provided by the High Plains Regional Climate Center.)

30 day precip map

 Figure 2.  Percent of normal precipitation from June 7 to July 6.Map showing departure from normal temperatures

 Figure 3.  Departure from normal temperature (F) from June 7 to July 6.

Whether you agree or disagree with the most recent USDA projections on planted and harvested acres, spring and early summer weather patterns still put a sizeable portion of the Corn Belt at risk for potential yield reductions. Fourteen and 30-day precipitation tendencies depicted in Figures 1 and 2 indicate normal to above normal moisture in much of the western Corn Belt from northern Kansas to the Canadian border, as well as Minnesota and southern Iowa. Dry pockets are materializing across eastern Iowa, northern Illinois, west central Wisconsin, southeastern Michigan, northeastern Indiana, and western Ohio.

During the past two weeks the upper air pattern has featured a persistent upper air ridge from the southwestern U.S. east through eastern Texas. Energy has rotated around the ridge’s periphery, resulting in significant rainfall across the Dakotas, Minnesota, Nebraska, western Iowa, and northern Missouri. Further east and northeast of this area, precipitation has been much spottier.

After the significant planting delay in Ohio (up to 7 million acres impacted), precipitation has averaged less than 25% of normal the past two weeks. Based upon the average emergence date for Ohio, corn is three to four weeks behind normal. Recent dryness will promote good rooting depth, but the crop is unlikely to silk before the end of July. Assuming normal temperatures from here on out, the risk of freeze damage before maturity stands at 70% or greater across the northern half of the state.

Less than 25% of normal moisture has fallen across eastern Iowa, northern Illinois, southern and western Wisconsin, and east central Minnesota. In a normal year crops would be close to pollinating, but the cool spring has delayed this process by 10-14 days. Producers on several ag blogs have noted the recent dryness and indicate that yields will likely take a hit if the recent precipitation trends continue for the next two weeks.

Heavy rainfall across the Dakotas has continued to cause flood related problems. High flows within the immediate Missouri River basin will continue at least through August. There have been numerous levee failures south of Omaha, but those north of the city have held up. It is uncertain whether they can hold up for another 45-60 days. Even if they hold, the water continues to destroy crops as water table levels rise further from the main river channel and flood fields due to water being pushed up through the soil surface.

In addition to flooding problems, below normal temperatures from April to now have resulted in GDD accumulations running less than 75% of normal across North Dakota and northern Minnesota. GDD accumulations are 90% of normal across the northern third of Nebraska to 80% of normal across northern South Dakota. If normal temperatures return for the remainder of the growing season, there is a 60% freeze risk across northern Nebraska and an 80% freeze risk for much of North Dakota.

Heavy rainfall across northern Missouri and southern Iowa has led to considerable low land flooding during the past two weeks. The persistence of the wetness leads to concerns in regard to shallow rooted crops that would be vulnerable to a quick heat wave and dry spell during pollination and grain fill.

South of Nebraska, heat and dry conditions are the rule of thumb, especially from central Kansas south into the lower Rio Grande River valley. The heat has come on strong during the past two weeks and appears to be stressing corn across southern and central Kansas, southern Missouri, and Arkansas. The models suggest that some of this heat will move north during the next two weeks, but these same models are flip flopping on how long the heat will last.

The core area of above normal temperatures during the past 30 days is easy to see in Figure 3. Average temperature departures are 4-10 above normal across the southern Plains and 2-6 above normal east of Texas and south of the Mason-Dixon line. This region has been battling a dry spell since early spring and the recent heat will likely affect grain fill. It wouldn’t surprise me if yield losses follow a similar pattern experienced across the central Corn Belt last year with the warm nighttime temperatures.

Nebraska Precipitation

Precipitation across Nebraska has been nothing short of astounding during the past 30-60 days. Going into this growing season, drought was a major concern due to the dry fall and early spring conditions. Rains in the last 7-10 days even eliminated the dry pockets across extreme southern Nebraska. Now the most significant concern will be air temperatures during pollination. With all of the heat south of us, it would be sickening to experience 100°+ temperatures during pollination similar to what our southern counterparts have seen.


There are considerable problems or potential problems within the fringe areas of the Corn Belt that will likely lead to significant yield declines and/or complete crop losses. Within the three big corn production states, recent dryness across eastern Iowa and northern Illinois could portend to major yield losses if the past two week precipitation trends continue through the end of July.

Excessive moisture across south central and southeast Iowa has likely led to shallow rooted corn that will be susceptible to even a short period (two weeks) of dryness. Flooding within the Missouri River basin will result in additional cropping acres being lost during the next 60 days along the Iowa-Nebraska border. The extent of damage will be determined by the integrity of the levee system and how far away from the presently flooded areas the water table rises and cuts off oxygen to the roots of growing crops.

Allen Dutcher
Extension State Climatologist


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