August 21, 2009

Welcome moisture finally fell across much of Nebraska August 14-16, helping alleviate moisture stress, particularly in areas of south central, central, and east central Nebraska. As producers enter the final stretch of the 2009 production season, it is time to look at some of the climatic issues that could still have an impact on yields.

Precipitation

Prior to the mid August precipitation, much of eastern Nebraska had been upgraded to abnormally dry conditions by the U.S. Drought Monitor. Within this area, moderate drought conditions were assigned to much of Thayer, Nuckols, Filmore, Saline, York, Seward, and Lancaster counties. With 3-5 inches of rain reported during the three-day period, most areas north of I-80 were returned to normal conditions. Abnormally dry and moderate drought conditions still remain south of I-80.

Recent rains return many areas north of Interstate 80 to normal precipitation levels.

Although there are pockets of dryness across western Nebraska, most locations have received enough moisture to put drought concerns on the back shelf. In fact, generous moisture events have resulted in normal to above normal streamflow rates on the Platte and Republican rivers the entire growing season.

Although the recent rainfall should temporarily halt crop stress, additional moisture will be needed to maximize production potential, especially in areas that have exhibited stress during the past 30 days. For the next two weeks, weather models indicate that precipitation is expected to below normal, with the best moisture chances falling prior to the start of September.

Temperatures

July 2009 was sixth coldest on record.

Although producers were able to get crops planted in a timely fashion, an unusually cold July resulted in crops falling 7-10 days behind normal. The statewide July preliminary average temperature of 71.1°F is currently ranked 6th coldest since 1895 and the coldest since 1992, which was the coldest July on record. An area from the Dakota's eastward through the Ohio Valley experienced its coldest July on record and crops are running two to three weeks behind normal.

Over the next two weeks temperatures are expected to be near average across Nebraska, with the western third of the state having the greatest likelihood of experiencing above normal temperatures. Even with normal temperatures, models indicate temperatures will fluctuate between below normal and above normal every three to five days. Therefore, it is unlikely that crops across the state will cut into the growing season deficits already accumulated.

Freeze Risk

With the planting delay issues common across the eastern Corn Belt this spring and record cold July temperatures, the fall freeze damage risk remains elevated. Using state agricultural statistics information and production estimates, approximately 1.2 billion of the projected 13.8 billion bushel corn crop has an above average freeze risk. The states at greatest risk are North Dakota, South Dakota, Minnesota, Wisconsin, and Michigan.

Even with delayed crops, Nebraska’s risk of an early hard freeze stands at less than 20%.

It will take normal to above normal temperatures and a hard freeze at least two weeks later than normal for these areas to escape significant damage. The situation this year is similar to last year and it took one of the latest freezes on record for much of the Corn Belt to escape damage. Even with delayed crops, Nebraska's risk of an early hard freeze stands at less than 20%.

With El Nino conditions strengthening in the equatorial Pacific, the probability of a later than normal hard freeze for Nebraska is likely if statistics hold true. Since 1950, there have been seven El Nino events that formed in the same year that a La Nina event dissipated. The years were 1951, 1957, 1963, 1965, 1968, 1972, and 1976.

Nebraska data indicates that five of these years experienced a hard freeze 7-17 days later than normal, with the remaining two years having a hard freeze 7-14 days earlier than normal. The average hard freeze data ranges from the first week of October in northwest Nebraska to the third week of October in southeast Nebraska.

Reservoir Levels

Lake McConaughy has benefited from the generous moisture pattern established since May across western Nebraska. Even though the central Rocky Mountain snowpack was below normal during the 2008-09 winter, heavy spring rains supplemented streamflow rates on both branches of the Platte River in May and June. Lake McConaughy peaked at 940,000 acre-feet, even with the release of 90,000 acre-feet from the Environmental Trust account.

Heavy streamflow rates on the southern branch of the Platte were diverted into the irrigation canals during May and early June, replacing water that would have been diverted out of Lake McConaughy. August 18 storage levels stood at 880,000 acre-feet (50.4% of capacity), about 60,000 acre-feet lower than its May peak elevation. McConaughy is 300,000 acre-feet higher than this time last year. As long as above normal temperatures and below normal moisture don't return to western Nebraska in the next month, McConaughy should remain above 800,000 acre-feet of storage.

Al Dutcher
Extension State Climatologist