U.S. Department of Agriculture defends weather models

Mar 1, 2013
by DTN

—Hangover drought a drag, not a disaster.

More than half of the country may be besieged by drought now, but such acute subsoil moisture shortfalls bear no correlation to yields come harvest, USDA meteorologists and crop forecasters told attendees at the Feb. 21-22 USDA Outlook Conference.

“I know it sounds counterintuitive, but it comes down to weather in June and July,” USDA ag meteorologist Brad Rippey said when attendees questioned USDA’s optimistic yield forecast. “History shows that even in the wake of the drought of 1988, it seems to be late spring and summer weather that determines the outcome for row crops.”

Although farmers in the Western Corn Belt remain skeptical, USDA is sticking by its forecast of trend-line corn yields of 163.6 bushels per acre and a monster 14.52 million-bushel crop in 2013. Production of that magnitude would slash season average cash corn prices to $4.80 in 2013-14, USDA said, pushing many growers below cost of production for the first time since 2009. It’s also a painful contrast to the expectation of record 2012- 13 corn prices of $7.20, the best profit year in grain farming in 40 years.

Too early to see a drought repeat

Persistent drought affects at least six of the top 10 corn states at the moment, but it poses only a “drag on yields” at this stage, not a definitive disaster, other USDA speakers emphasized.

USDA economist Paul Westcott acknowledged that Iowa’s January Palmer Drought Index ranks as the 10th-driest since 1895 (see table below), and record drought is worse in Nebraska, South Dakota and Kansas. But rather than subsoil moisture in late winter, USDA weather models found three scenarios are better indicators of future yield: planting before mid- May, large deviations in June rainfall, and July heat and precipitation. All of those factors are unknown in mid-February and make long-term forecasting precarious.

USDA’s weather model incorporated trends from 1988 to 2012, so it included two major droughts. The model monitors only eight states—Iowa, Illinois, Indiana, Ohio, Missouri, Minnesota, South Dakota and Nebraska—since they account for about three-fourths of U.S. corn production.

Early planting progress before mid-May increases yield expectations by helping the crop avoid pollination stress, Westcott said. In the 2012 season, USDA figured this boosted potential yields to 166 bpa on average. When June rainfall nationwide fell 2 inches short of average, it knocked 18.7 bpa off national production, according to USDA weather models. Then July heat and scarce rainfall roasted the crop at pollination, slashing another 22.7 bpa below potential.

Imperfect science

One flaw in government weather data is its difficulty in forecasting the kind of flash drought that caught meteorologists off guard in 2012, Anthony Artusa of the Climate Prediction Center in College Park, MD, said.

A year ago, soils were insufficiently recharged due to lack of snowpack and March’s record heat. When the country experienced a rapid onset of heat in late June, moisture reserves were quickly depleted. During May-July 2012, models underestimated the amount of heat in the forecast and “missed the mark” on precipitation, Artusa said.

Misgauging summer precipitation is critical, since the Grain Belt receives 35 percent to 60 percent of its annual precipitation in May to July, with North Dakota at the high end of that range, he added.

Unfortunately, weather models don’t give a clear signal on summer precipitation when so-called El Nino Southern Oscillation neutral conditions occur, he added. Those are the kind of years when neither El Nino nor La Nina patterns dominate. That’s also the kind of year that’s shaping up for 2013, Artusa noted, so weather surprises could again materialize later in the season.

“It’s very difficult to catch these flash droughts in advance,” he said.

DTN Senior Ag Meteorologist Bryce Anderson agrees there is no question that spring and summer weather are the drivers behind final corn yields, but he doubts a perfect trend-line corn yield will materialize, even with favorable summer weather.

“Forecast models are all crowding the summertime Pacific temperature trend in the ‘neutral’ category, and with that forecast, DTN looked at similar years when the Pacific was coming out of a La Nina and into a neutral phase,” Anderson said. “We found that spring and summer temperatures were near to below normal (favorable for crops), but on precipitation, spring is near to below normal and summer is almost entirely below normal.

That does not provide the support to boost yields to the kind of bumper crop that USDA is talking about. Is it a big improvement over last year? Certainly. But 163-164 bpa? At this point that seems questionable.”

At the moment, Artusa and other government forecasters expect drought conditions to improve over the next few months in a band that includes western Minnesota and western Iowa.

However, he’s not ruling out the risk of another flash drought recurring in 2013.

USDA’s Rippey agreed there’s much uncertainty in the ultimate harvest at this stage. USDA’s drought monitors are showing extreme moisture shortfalls a meter deep in key Corn Belt states west of the Mississippi. In places such as Nebraska, western Minnesota and northwest Iowa, some irrigation wells and rural water systems already are running on empty.

“We’ve transitioned from an agronomic drought to a hydrologic drought” in those cases, Rippey said, predisposing crops to stress. Under the right conditions, he added, “a flash drought could roar back very quickly.”

Palmer Modified Drought Index -- Jan. 2013

PMDI low ranking since 1895

Iowa 10

Illinois 45

Nebraska 5

Minnesota 13

Indiana 64

S. Dakota 6

Wisconsin 38

Ohio 91

Kansas 9

Missouri 14

Example: In January, Iowa ranked in the 10th-worst condition for drought since 1895, but Illinois, Ohio and Indiana fared much better. However, USDA found no statistically significant match to January drought and final yield during the last 25 years of weather records. (SOURCE: USDA) — Marcia Taylor, DTN