These Dark And Stormy Nights

Rain is good for shallow-rooted corn at pollination time.

In July, Iowa has been having a pulse of thunderstorms coming across the state, skipping a couple of days, and then coming through again. "This has been a favorable weather pattern for 2008 crops," says Elwynn Taylor, Iowa State University Extension climatologist.

"We've had some hail and heavy wind in local areas. But rain in July has been the salvation for crops this summer--which have been delayed in development because of floods, excess water and cool weather in May and June."

Good for shallow-rooted corn

The wet spring resulted in shallow root systems this year. "If Iowa would have gone to hot, dry weather during July that would have been the end of a lot of our crops in many fields this year in Iowa," says Taylor. So it's been a good thing to have thunderstorms in July, he adds.

As corn and soybean crops are now entering the reproductive stage, Iowa is still behind normal in crop development. This map from ISU Extension specialist Rich Pope, who keeps track of this data, indicates where crops currently stand on degree-day accumulation.


"Iowa needs warm, sunny days with cool (lower 60-degrees F range) evenings and periodic rainfall as ideal growing conditions," says Pope.

Warm forecast for State Fair

Looking ahead to August, what kind of weather does Taylor think we'll have for the Iowa State Fair? That's a 10-day period from August 7 to 17 in Des Moines. "Of course, it has to be warm," he says. "It's the State Fair. And that's exactly what the forecast from the National Weather Service predicts. I anticipate it will be warm, with near-normal chances of rain as we go to about mid-August. That's as far out as the Weather Service forecast goes—to August 14."

The forecast is for generally dry weather in eastern Iowa—east of Des Moines, for State Fair time. The forecast is for about normal precipitation in Des Moines and central Iowa and to the west in Iowa. For the State Fair—Taylor agrees with this National Weather Service forecast and looks for a little warmer than usual temperature and normal chances of precipitation the first half of August.

Will first frost be delayed?

What does Taylor think Iowa will have, regarding a date for the first killing frost this fall? "We do have one clue finally, on first frost other than it just coming at its average time," he notes. "There is no specific guess as to when the first killing frost will hit. But the longer range outlook from the National Weather Service is indicating the chance that October will be on the warm side of usual, and so will September."

Crops are running behind schedule, so farmers won't mind it being on the warm side of usual this September and into October. "That forecast gives us an increased probability that the date of the first killing frost will be delayed," says Taylor. "I'm not sure that will happen but at least this new weather forecast indicates that a later than usual first frost this fall could happen."

Need warmer than normal fall

So, Taylor's prediction, based on interpreting the National Weather Service longer range forecast for temperatures into fall, is that Iowa could have a warm, late fall. "I think that would be very welcome," he adds. "If we could push that first frost date back to the end of October, farmers with late-planted and replanted corn and soybeans would breathe a lot easier."

The normal dates for first killing frost are early October in northern Iowa, mid-October in central Iowa, and later in October for southern Iowa.

What are the chances of an early frost occurring? There is less chance of that happening, says Taylor. The La Nina weather event that was occurring from January into March this year has disappeared. "That means the chance of an early frost is reduced," he notes.

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