What Are Chances For Early Frost In Iowa?

What Are Chances For Early Frost In Iowa?

Possibility is higher than normal since we are still experiencing a La Nina year and the weather pattern that comes with it, says ISU's Elwynn Taylor. But he doesn't see any indication of early frost occurring, not yet anyway.

News reports circulated in the futures market in Chicago last week about the possibility of an early frost occurring in the Corn Belt this fall. What is the chance for any such thing happening in 2011? Iowa State University Extension climatologist Elwynn Taylor says there's a good possibility it could happen.

The possibility is higher than it would be in an "average year," he says. That's because this year started off in a La Nina weather pattern, and we've had these extremes in weather beginning last October all the way up until now. That is, warm week, cold week, warm week, cold week etc. "And when you are in a La Nina, the chances of having an early frost in the fall is greater than it is in just a year drawn out of a hat," says Taylor.

La Nina weather pattern still with us, indicating weather uncertainty

He adds, "I think maybe people are starting to realize that contrary to what a lot of news reports have said over the past month or two, La Nina is still with us, from at least the scientific definition of a La Nina. Since it hasn't gone away, and the U.S. Weather Service has now acknowledged that they think La Nina will still be with us as the calendar moves into fall, it becomes a thought in peoples' minds that yes, an early frost is a possibility. Just as it was back in 1974 when we had a La Nina weather pattern and had an early frost. In that year we had a La Nina that dragged on and re-strengthened in summer and fall. And we did have a very early frost in the fall of 1974 in the Corn Belt."

Are there any indicators that would give you an advance warning of such an event occurring this fall? "About the most advanced warning we can get on an early fall frost, that a real hard freeze event is coming, is about four or five days ahead of time," says Taylor. "In other words, it has to actually be on the road and heading toward the area of impact. Then we see it moving and if it keeps moving this way, we'll have a frost here. Right now, that isn't the case. We don't see it out there currently. But weather forecasters will be keeping an eye out for such developments this September and into October."

Outlook for harvest weather uncertain, as computer models show

If we have cooler weather in September, does that increase the likelihood of early frost? You have to watch what's going on in North Dakota and northern Minnesota, says Taylor. But as far as the central part of the Corn Belt is concerned, an early frost doesn't seem to be a real threat at the moment.

After a surprisingly hot, dry summer in much of Iowa in 2011, weather forecasters say the harvest outlook remains uncertain. Some computer models point to a wet, warm fall, while others indicate cool, dry conditions.

"It's not clear-cut at all," says Harry Hillaker, state climatologist at the Iowa Department of Agriculture in Des Moines. "The U.S. Weather Service has issued its outlook for September, October and November and it slightly favors warmer than normal and wetter than normal conditions. But there's also some indication that we're entering back into a La Nina event, which would be just the opposite—cooler and drier than normal."

Summer heat was extreme, pushing Iowa crops to mature quickly

In either case, it will be hard to beat last fall's weather for harvesting. Farmers enjoyed an extremely dry period that began in late September and persisted into he second week of November, allowing combines to roll almost uninterrupted. It brought crop moisture down to levels that made additional drying of grain in the bin virtually unnecessary in many cases. That was an extreme contrast to 2009, when Iowa had its wettest October in more than a century. Typical rainfall for Iowa for the month of October is around 2.5 inches.

Typical dates for the first 32-degree temperatures in Iowa in the fall are late September in northern Iowa, early October in central Iowa, and mid-October in southern Iowa. However, Hillaker points out that the hot temperatures in July and early August of 2011 helped speed crop development, which means most crops in the state will be mature before the first killing frost hits this fall—if it occurs when it normally does. "With the very warm temperatures we've had this summer, there's very little concern about crops not being mature and dried down at harvest time this year," he says.

TAGS: Extension
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