The Chicago ags have had an explosive upmove. The immediate cause was the forecast for dry weather for about a week or so. This is the first hint of unfavorable growing weather in years.
But the real reason for the explosion is the position of speculators. Managed money (primarily CTAs) were heavily short corn and soybeans and somewhat short soft wheat. So this is mostly them getting blown out. Of course, if the forecasts continue to be dry, we will probably get them long as well.