Friday morning, grain futures were running high, posting double-digit gains until about the middle of the day, when a new forecast was released. Then, with an almost laser focus on Mother Nature, traders took improved rainfall chances and ran with them to trim early gains, leaving the grains to finish the day just slightly higher.

"Midday forecasts call for more moisture after next week, but the forecast could still switch back again, and more rain will still be needed to prevent yield losses in any case," according to a report from Dow Jones Newswires.

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Weather outlook shifts like this have traders on edge, making for a volatile marketplace, one trader told Agriculture.com Markets Editor Mike McGinnis on Friday.

"Weather is as always a big factor and we've got boatloads of it here and abroad to talk about," the trader said Friday. "Traders simply can't assume anything will turn out as it may seem."