Remember that old Chicago adage that "if the bears have Thanksgiving dinner, bulls will have a Christmas feast"?
It looked to be coming true heading into the week running up to Christmas, as grains put a distance between themselves and the multi-month lows hit last week.
External markets were hardly helpful, with the death of Kim Jong-il, the North Korean leader, raising doubts about stability in the region.
Shares closed lower in Europe, down 0.4% in London, and lost a similar amount in New York in late deals, even though concerns about the eurozone appeared to be stabilising, for now.
The broader weakness did its bit in depressing some soft commodity markets, with New York
However, it was no match for the mounting concerns over South American weather, which finally spread from
The problem is the dryness in southern Brazil and Argentina, blamed on the La Nina weather pattern, which appears to be bedding down.
"Most of the talk is about dry conditions in South America," Darrell Holaday at Country Futures said.
Why this matters now is that corn is approaching the sensitive pollination phase, with some soybeans in pod-filling too.
"Recent weather models indicate that La Nina may be strengthening, which could result in a drier weather pattern continuing into the reproductive phase of row crop development in this region," Benson Quinn Commodities said.
US Commodities estimated that about "50% of Argentina is in need of moisture", with about one-third of Brazil too, even assuming rain kicks in as forecast this week.
And this when some "20% of the first corn crop in Argentina is pollinating and about 40% of the Brazil corn. The market is adding risk premium".
OK, much harm might be reversed in February if the La Nina fades in time – as happened this year, WxRisk.com said.
But investors were not taking any chances, especially when they have already sold down heavily in the main Chicago crops, as revealed by futures and options data, raising ideas that there may not be much appetite for further sales for now.
"The reality is that these markets are oversold and when they ran out of sellers at the lower prices last week, it prompted some significant short-covering," Mr Holaday said.
That went for Chicago
The problem this time was damage from dryness in Argentina earlier in the season, which curtailed development of the important Buenos Aires state crop.
"Heavy rainfall finally developed in November, replenishing field moisture in Buenos Aires. It was too late for wheat to recover," Gail Martell at Martell Crop Projections said.
Argentina's farm ministry slashed by 1.5m tonnes to 12m tonnes its estimate for the ongoing harvest, which is some 50% complete.
Signally, the ministry's new estimate is 2.5m tonnes below that the US Department of Agriculture, whose data set global benchmarks, made 10 days ago.
This is especially sensitive when Argentina has been heavily discounting wheat, becoming the international price leader, to clear the decks of old crop to make way for new.
And chances are the previous price leader, Russia, will not regain its grip even if Argentina does pull back on discounting, given that wheat merchants in the Black Sea state have already taken the low-hanging fruit, as it were.
"A significant decline of stocks in southern export-oriented regions and the need to deliver grain to Black Sea ports from distant regions raises expenses and cuts the competitiveness of Russian cereals," SovEcon, the Moscow-based analysis group, said.
"It is the market," and not potential government curbs on shipments, "that will lead to a significant decline of Russian grain exports in the first half of the 2012 calendar year," SovEcon said.
The idea of weakened Argentine and Russian competition boosted wheat prices in Europe, another major competitor, too.
Paris wheat for March added 2.0% to E182.50 a tonne, its highest close for more than a month.
Ditto London's best-traded May contract, which closed up 1.9% at £146.70 a tonne.