Martell: Coolness Giving Way to Heat as Midwest Drought Persists

August 19, 2013 05:03 AM



The following content was provided by meteorologist Gail Martell of 

Coolness Giving Way to Heat as Midwest Drought Persists

Prolonged dryness in the Midwest is taking a toll on corn and soybeans. Maximum temperatures over the weekend were 2-3 F higher than the GFS model predicted in Iowa and Illinois.

Midwest Drought Worsened Late July August

When fields become extremely dry, there is less evaporative cooling which, in turn, increases surface temperatures. Corn leaves begin curling in the afternoon to conserve crop moisture. This slows down plant activity hindering kernel filling. Soybeans are more drought-resistant than corn, hanging on and waiting for rain. Yet prospects have slowly deteriorated from reduced rainfall in recent weeks, the US good-excellent soybeans falling to 64% good-excellent August 11, compared to 67% the month earlier.

Corn conditions are expected to move lower in Iowa, Illinois, Wisconsin, Minnesota, Indiana and North Dakota in the August 19 crop progress report today. The dry August follows on the heels of sub-par rains in July.

August Drought Threatening Soybeans

Soybean damage may be worse than corn if the drought persists. August rainfall is the key determinant of the yield. Very heavy rains optimize the yield. Rainfall has been sparse in Iowa and Illinois, the 2 leading soy states. Also very dry in August are Wisconsin, North Dakota, Missouri and Upper Minnesota placing roughly 40% of US soybeans at risk for a reduced yield.

hotter Temps  Wed Nebraska Iowa

Worse conditions in soybeans are anticipated in the August 18 report, as the yield-sensitive pod filling period advances. Fifty-eight percent of soybeans were setting pods a week ago. Perhaps 75% will have reached that key stage this week.

Strong Midwest Warming

After weeks of coolness the weather pattern is turning hotter. The jet stream would build up a warm, stable ridge of high pressure over the heartland, ratcheting up temperatures in the central United States. Moderate temperatures, mid 80s today, would give way to upper 80s-low 90s F by Wednesday in Nebraska, Iowa, Missouri, Illinois and Wisconsin.

Heating Begins Tuesday Evening

The Tuesday evening forecast shows hot air encroaching on the Midwest from the Great Plains.

The GFS model sees just light rainfall in the 5-day forecast for Midwest corn and soybeans. This is due to the stabilizing influence of high pressure aloft. The jet stream forecast is for a large, stable ridge to develop over the central United States. Hardly any rainfall occurred last week in the Midwest.

Monday Friday Rainfall Forecast

A few showers are anticipated in the Upper Midwest - "ridge-rider" thunderstorms, in Iowa, Minnesota, northeast Nebraska and western Wisconsin Wednesday night-Thursday. However, high pressure would keep most of the Midwest dry.


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