Ag Weather Forum
Bryce Anderson DTN Ag Meteorologist and DTN Analyst

Wednesday 07/10/13

Prime Crop Weather Time Is Here

Weather market season is once again upon us. And even though we all know that this part of the year is extremely important, the significance and the implication for production is to me quite astounding. Analysis of corn and soybean production impact from weather conditions in July, August and September by Informa Economics shows these swings in corn and bean output:

Looking at the last ten years of production estimate changes from USDA’s initial August crop reports to the final estimates, the Informa analysis found that for corn, the final crop estimate has risen by as much as 884 million bushels (in 2004) compared with USDA’s August forecast and has fallen by as much as 918 million bushels (in 2010). Adding those totals together, you get a resulting range of 1.8 billion bushels. The average absolute change for corn from the August report to the final over these 10 years has been 421 million bushels.

For soybeans, the final crop size as checked by Informa shows a rise by as much as 323 million bushels (last year 2012) compared with compared with the August forecast; and a decreased of up to 444 million bushels (in 2003). This results in a range of 767 million bushels. The average absolute change following the August report to the final for soybeans has been 191 million bushels.

What's the message here? Does this call into question the forecasting ability of USDA? That may be argued; however, Informa's interpretation is that these wide variances "strongly support the reality that fall crop yields are dominantly determined by July, August and September weather (for row crops) which obviously has not been realized prior to USDA’s August Crop Production report."

Just look at last year. The blistering hot and dry July weather pattern reduced the final corn yield by about 18 bushels per acre, and August's weather knocked another 2 bushels an acre off that figure. So, combined, weather experienced during July and August last year resulted in a 20-bushel-per-acre reduction in U.S. corn yield. On the other hand, favorable July and August weather in 2009 resulted in a 13-bushel-per-acre increase in final yield.

So what's happened so far this year during July? According to Midwest Regional Climate Center data, the mean temperatures for the July 1-8 period in the Midwest were generally in the range of 70-75 Fahrenheit. Looking across the region, the areas where that temperature range was above normal were from northern Iowa through Minnesota and the eastern Dakotas, along with eastern Ohio. All other areas were normal to below normal--with the southern two-thirds of Illinois, along with most of Missouri, Indiana and Kentucky in the range of two to six degrees F below normal.

In a typical year, of course, these temperatures would sync up with corn pollination and soybean blooming in quite a few areas. But this year, with crops so far behind (corn just six percent silked compared with 20 percent average, and soybean blooming at only ten percent compared with 24 percent average), that mild start to July just meant a favorable run of plant development. The "main event" is yet to come--which is why Wednesday's ten-day forecast of a very warm to hot and dry scenario for the central U.S. has received a lot of attention.

I am still very impressed by those swings in production from that Informa analysis. 1.8 billion bushels on corn and 767 million on soybeans at the extreme--that's a big deal.


Twitter @BAndersonDTN


Posted at 9:36AM CDT 07/10/13 by Bryce Anderson
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