Martell: Midwest Weather Pattern Turning Wetter and Cooler

July 29, 2013 05:40 AM


The following content was provided by meteorologist Gail Martell of 

Scattered showers and cooler temperatures last week made a positive difference in Midwest corn and soybeans. Crop conditions are expected to stabilize or improve slightly in the USDA July 28 report due today. One third of the Midwest received moderate- heavy rainfall last, at least .50 inch. Showers were especially beneficial for corn, now in the midst of pollination, following a prolonged stretch of extreme heat and dryness in Iowa, Nebraska, Wisconsin, western Illinois, Missouri and Kansas. Corn "silking" was only 43% along July 21.

Observed Rainfall 32 days ending July 28

While the recent rainfall was beneficial for drought stressed corn and soybean, exceptional coolness has slowed down crop development. Maximum temperatures Saturday were only 60s F in Wisconsin, Minnesota and eastern Iowa and 15-20 F below average. Strong cooling is a setback for corn and soybean development in the Upper Midwest, especially, due to severe planting delays in Iowa, Minnesota, Wisconsin and North Dakota.

Cool and Damp Forecast Upper Midwest

Below-average temperatures are expected to continue this week in the Midwest. Mid 70s F for highs and 50s-low 60s F for low would be the rule. Unusual coolness is due to a blocking pattern in the high latitudes, over Canada, diverting the jet stream south of its normal position.

Cool Midwest Forecast

Waves of light-moderate showers are predicted across the Upper Midwest in an unstable, humid atmosphere. Scattered locations may receive up to .75 inch of rainfall. This would further improve corn and soybeans in dry areas of Iowa, southern Minnesota, Wisconsin and northern Illinois. However, with cool temperatures also expected to continue crop development would fall further behind.

Wet Forecast in Drought-Stressed Heartland

Showers developed overnight in Nebraska the driest of the main corn states. A trough of low pressure is developing. This would promote 1- 1.5 inches of rainfall over the next 5 days. Kansas is expecting super-heavy rainfall, up to 4 inches. The wet forecast is significant, since both states presently are severely dry.

5 Day Rainfall Outlook

Kansas corn deteriorated to only 31% good-excellent in the July 21 report from USDA. Nebraska, the 3rd biggest US corn state, declined to 66% good-excellent, down from 78% on July 1. Soybeans also were severely stress by heat and drought. Good-excellent soybeans in Nebraska fell to 63% last week, down -15% from 4 weeks earlier. Kansas soybeans were only 41% good-excellent and down 26% .

ENSO Signal Undergoes Major Shift

Heartland drought is a classic symptom of the La Nina effect. This climate anomaly seemed to be gaining strength over the past 4-5 weeks, as cooling occurred in the eastern equatorial Pacific Ocean, the Nino 3.4 region. Suddenly the La Nina signal began fading, as the eastern equatorial seas have warmed. A modest El Nino signal is emerging, a "wet signal" in the United States heartland.

Eastern equatorial cooling in July

Scientists at the Climate Prediction Center have held with a "ENSO-neutral" forecast through end of summer, neither La Nina or El Nino. That does not mean "average" weather as July was extremely dry in the heartland and the emerging weather pattern is wet.


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