(DTN) -- The market weather scenario for corn going into fall 2010 is more complex than in other years.

Typically, dry and mild harvest weather favors lower prices, because of a brisk, ready supply of high-quality grain. Cold, blustery weather favors firm to higher prices, due to slowdowns and possible yield and quality loss.

However, in 2010 that trend is shaken up a bit. Even dry and mild weather likely will offer no worse than a neutral market weather factor.

The reason is that corn harvest is already forecast to be lower than projections earlier this year. Much of that lower expected output is due to adverse weather during the last half of summer, especially in the southern Corn Belt, where hot and dry conditions hindered corn fill.

"With ending stocks-to-use falling to the second tightest level in over 40 years, the market should remain well-supported through harvest," said DTN Analyst John Snow. "If pronounced harvest delays develop due to wet weather in key growing areas, it would provide additional support."

HARVEST DELAYS LIKELY

Harvest delays are likely this fall. Telvent DTN Ag Meteorologist Mike Palmerino said changes are underway which pose a challenge to harvest work going into the last half of September.

"We are seeing the pattern transitioning; mainly, it's cooling in Canada. So, we are likely to see a return of the cold north, warmer south boundary in the Midwest that we saw during much of this season," Palmerino said.

Another upper-atmosphere trend shaping up is the return of blocking high pressure to the far northern latitudes. This feature prevents storm systems in the Gulf of Alaska from moving east into Canada; this forces storms southeast through the north-central U.S.

"I'm seeing a lot of blocking in Alaska, the Arctic, Greenland, pretty much all around Canada," Palmerino said.

PROFOUND IMPACT

The impact of this blocking is profound; its presence means that a storm track, once it sets up, can settle in for several days at a time. This consistent pattern is what brought record-or near-record rain to Iowa during each summer month. It's also the culprit in the mid- to late-summer drought which has shaved corn production prospects south of Interstate 70.

"It's a bit of a tough call, but the two areas for potentially wet harvest weather are in the Plains and the Western Corn Belt," Palmerino said. "And I would say that the Western Corn Belt has the highest risk of wet weather for harvest disruption. Rainfall of two to four inches during a single episode is possible."

Being more specific, Palmerino cited much of the wettest Midwest area from this past season as the target for potential harvest-delaying rain.

"I think again you need to look at that corridor of Interstate 80 to Interstate 90 and west of Des Moines, Iowa," Palmerino said. "I don't want to short-change Minnesota either regarding the rainfall potential."

Elsewhere, prevailing cool or already-dry conditions are likely to influence harvest weather, Palmerino said.

"In the upper Midwest and Northern Plains, they are actually far enough into the cooler air that it stays drier," he said. "It's the same situation for the Eastern Corn Belt. And in the south, we will likely see continued high pressure influence to maintain a drier weather pattern for the continuation of harvest."

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