June 20, 2008

Weather trends continue to cause problems across a large swath of the Corn Belt, with Iowa being particularly hard hit this production season. Eighty-three of Iowa's 99 counties have been declared disaster areas due to prolonged flooding. In addition, east-central Illinois through central Indiana were inundated with 6-12 inches of moisture during a two-day stretch less than two weeks ago.

Most of Nebraska finally caught some relief during the past week (ending June 17) as heavy rainfall was limited to southeastern and east central portions of the state. Western Nebraska received additional moisture, but no significant flooding was reported. Flow on the Platte River west of Grand Island has finally returned to normal. East of Grand Island, the Platte is running in the upper 20% of historical flows, but has dropped below flood stage at all recording sites.

The damage from this endless train of storms is profound, with assessments changing daily. In Nebraska, the latest estimates are that 500-600 center pivots were damaged or destroyed by strong thunderstorms and tornadoes. Although widespread flooding has been reported across the eastern two-thirds of the state, it appears that less than 5% of the corn acreage will be lost.

Corn Belt Losses

The same can not be said for Iowa. The Iowa Farm Bureau estimates that 1.3 million acres of corn have been destroyed from flooding and saturated ground. Total Corn Belt acreage loss is currently estimated at 1.5 - 3.3 million acres. As water slowly recedes in Iowa, flood surges greater than 1993 will move down the Mississippi River during the next two weeks, engulfing additional river bottom acres.

Some of Iowa's most productive soils are in the central and north central areas. These areas have escaped the magnitude of flooding witnessed in Cedar Rapids, but soils are water-logged and will take a week or more of dry weather to drain. Iowa's Ag Statistics Office reports that 8% of the corn acreage was replanted, with 9% was affected by some level of flood damage. As of Tuesday damage in Illinois was not as significant as in Iowa, however 6% of the corn crop still had not emerged. The average height of the corn crop is a mere 12 inches compared to a normal height of 28 inches and 35 inches last year. During the past 10 years only 2002 came in at a lower average crop height at 11 inches. Indiana, the fourth largest corn producing state, currently has 93% of corn emerged, with replanting accounting for the remaining 7%.

If the Corn Belt experiences ample dry weather soon, national crop conditions will likely hold steady or improve slightly during the next few weeks.

Pollination Concerns

The next test for this crop will be in July. With waterlogged soils and cool spring temperatures, crop development is now 10-20 days behind normal east of Nebraska. Without a significant heat wave, most of the corn crop will enter pollination during the last half of July, with replanted acreage entering pollination in late July or early August. During these periods the Midwest usually experiences higher temperatures that are not conducive to pollination.

In Nebraska, temperatures were below normal in May, but have been normal to slightly above normal in June. Our best estimate is that the corn crop is 7-10 days behind normal, with much of the delay directly related to late emergence. Most of the corn crop is expected to enter pollination July 10-17 if the current temperature trend continues.

After pollination, concern will shift to late summer and early fall conditions. A broad area extending from northern Minnesota southward though Wisconsin and northern Iowa will need normal to above normal temperatures, coupled with a later than normal hard freeze, to escape additional yield damage.

Forecast for Change

Weather models do indicate a movement away from the extreme wetness experienced during the past 30 days. Upper air ridging over the southern Rockies will gradually work north and east, bringing warmer conditions and less intense rainfall to the central Plains. Instead of surface systems moving out from southeastern Colorado, most will come over top of the upper air ridge from North Dakota and Montana.

Since most of the systems expected to impact the central Plains will be moving southward, they won't have as much moisture to work on. During the summer these systems tend to be quick hitters, dropping brief, intense rain before ushering in drier weather. This would be a radical change from the past 30 days where thunderstorms would reform over the same areas, producing rains of three inches or more.

As we move into July, we'll want to watch whether this pattern becomes firmly entrenched or is a temporary lull before excessive rains return to the Corn Belt. If the upper air ridge builds into the central and northern Rockies, this would push the main storm track north and east of Nebraska and bring the heat and dryness engulfing the western half of Texas northward. By the end of the month, we should have a clearer picture of the mean jet stream pattern.

Al Dutcher
Extension State Climatologist