Martell: Still Not Enough Rain for Corn and Soybeans

July 22, 2013 05:31 AM

The following content was provided by meteorologist Gail Martell of 

Midwest showers were lacking on the weekend, with a few areas getting moderate rainfall but the vast majority of the grain belt remaining dry. A weak Canadian cool front today will drop southward through the upper Midwest, but only light rainfall is predicted in Iowa, South Dakota and Minnesota. Another stronger Canadian cool front is predicted late in the week Friday through Saturday, triggering heavier upper Midwest rains.

Light Rains Last Week in Midwest

By then, a significant portion of corn will already have pollinated under very dry conditions. By July 14, only 16% of U.S. corn had silked. The key pollination stage is delayed this summer due to late planting dates. Over the past week, United States corn silking may have advanced to 38%. Soybean blooming is expected to reach 30%.

Corn and soybeans conditions are expected to decline in the July 21 report from USDA due to ongoing drought and heat stress in the Midwest. Nearly half of U.S. soybeans were planted in June. These are particularly vulnerable to drought stress from a shallow root system. Less than 10% of U.S. corn was sown in June.

Iowa Drought Most Severe

The top U.S. corn and soybean state Iowa is also the driest, with most farms reporting less than 20% of average rainfall month-to-date. The topsoil has grown very dry. It will take a heavy soaking rain to replenish parched fields. One-half inch would not be enough. Producers are growing rather weary of wet forecasts that have not materialized.

Jly Rainfall as Percent of Normal

July Rainfall Deficit in Inches

Drought in the Midwest may be associated with an emerging La Nina signal. Sea surface temperatures have chilled down significantly in the eastern tropical Pacific Ocean in the recent month, consistent with La Nina. For its part, the Climate Prediction Center is sticking with a "ENSO-neutral" forecast. The dry weather pattern in July tells a different story.

Midwest Rainfall May Increase this Week

The GFS model is keeping with a rather dry Midwest outlook Monday to Wednesday, but it becomes much wetter later in the week. The upper Midwest is expected to receive 0.50-0.75 inch of rainfall, but more locally in the range of 1-1.5 inches in northern Iowa and Minnesota. Showers may develop along an unstable cool front that drops out of Canada. But producers are growing weary of wet forecasts that have not materialized in the extended outlook.

Much cooler temperatures in the mid 70°s F to low 80°s F are predicted this week in the Midwest. Hot conditions are predicted in Kansas, Oklahoma and Texas, maximum temperatures near or above 100° F. The heat wave in the central Plains would moderate when a cool front descends into Kansas later in the week. Heavy rain may also be coming to Kansas. However, Texas could remain very hot, along with the southwest desert.

7d GFS rainfall

Discouraging 6- to 10-day Outlook

The 6- to 10-day forecast is cooler in the Midwest but also dry. Without significant rainfall, corn and soybeans would continue to go downhill from already dry field conditions. As the pollination stage advances in corn, plant moisture needs would sharply increase. Any moisture stress during that period would result in reduced kernels on the ear. Flowering soybeans would also be taxed by drought. Late-planted soybeans are shorter than average and carry fewer blooms.

6 10 Day Temperature Outlook 6 10 Day Rainfall Outlook


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