Growing season weather yet to be decided
By Jean Caspers-Simmet
Date Modified: 06/28/2012 2:13 PM
BOONE, Iowa — Elwynn Taylor says he won't know what the weather will be like for the rest of the growing season until July 10.
"By July 10, we will know if we're headed toward a mild August and September or a harsh one," said the Extension climatologist during a presentation at last week's Farm Progress Hay Expo.
Don't expect much rain between now and July 4.
"We're expecting it to be on the dry side," Taylor said.
Oceans control the weather even for states in the middle of the country, Taylor said.
About 85 percent of the moisture that falls in the Midwest comes from the Gulf, Taylor said.
"We have to have moisture in the air plus a disturbance in the atmosphere to get rain, and the disturbances this past month have mostly been in Minnesota where they're getting ample rain."
Taylor said that Interstate 35 divides the country's weather. West of Interstate 35, the weather is controlled by the Pacific Ocean. For those east of I-35 to Ohio, the Gulf of Mexico and Bermuda High Pressure influence it.
"There is so much energy held in the top 4 inches of ocean water," Taylor said. "It's equal to the energy held in the atmosphere from the ground up 50 miles. If ocean water is heated or cooled down 50 feet, it could take up to a year to dissipate. That's the kind of control La Nina has had on the weather on both sides of I-35 the past two years."
La Nina — generally not the farmer's friend — caused the weather to shift from a wet year in 2010 to a very dry year in 2011.
"On about July 11, 2011, the rain quit," Taylor said. "With the rain over and La Nina back to full strength, it whittled down the crops. In January 2011, I said the national corn yield would be 147, and it came out 147.8 bushels."
Taylor said the weather was the same in 1974 and 1956, the two other strongest La Ninas. He has looked at the 10 strongest La Nina events in the past 110 years. All lasted into the third year and 2012 is the third year of the current event. All faded to neutral conditions in March to May of the third year, just like this year.
"When you have a tire swing, and you let go of the tire, it doesn't swing to the middle and stop, it swings a long ways to the other side," Taylor said. "You don't expect the weather to go to neutral when it's been record distance to the other side. You expect it to swing the other way. That is from La Nina to El Nino, the Midwest farmer's friend."
During El Nino it isn't oppressively hot, record-setting cold or excessively dry in the Midwest, Taylor said.
Of the 10 strongest La Ninas, four went from neutral back to La Nina by August of the third year, destroying corn, hurting soybeans and putting an end to forage crops. Taylor said. Six went past neutral and into El Nino.
"The one thing we do not expect is that it will stay neutral or average in July and August," Taylor said. "Do expect that what you've got already, you've got. We have taken a bit of a beating, and there's a 60 percent chance crops will recover based on the odds of what it's done in the past."
Farmers should pay attention to the July 10 forecast, Taylor said.
"By then, we'll be able to tell if we're going back to La Nina or going into El Nino, and then we will have a very reasonable outlook for the rest of the year," Taylor said.