As much as 15 percent of winter-wheat plants in the Great Plains face damage, Kyle Tapley, a senior agricultural meteorologist at MDA Weather Services in Gaithersburg, Maryland, said in a telephone interview. The potential for frost will increase in Florida tonight and tomorrow as temperatures drop to the upper 20s Fahrenheit, damaging citrus groves, he said.

Livestock slaughter will slow because it's harder to transport animals in the cold and snow, and cattle will have trouble gaining weight, according to commodity broker Allendale Inc.

?The coldest air in almost 20 years is sweeping over the central U.S. toward the East Coast, threatening to topple temperature records and ignite energy demand. Hard-freeze warnings and watches, which are alerts for farmers, stretch from Texas to central Florida, and 90 percent of the contiguous U.S. will be at or below the freezing mark today, according to the U.S. Weather Prediction Center in College Park, Maryland. Wheat futures headed for the biggest two-session gain in more than a month.

Eoin Treacy's view

So far, the cold weather has had the greatest effect on Live Cattle prices which have moved to a new high, having ranged below $135 for nearly two years. It will probably be a while before we have greater visibility on how much damage has been done to orange and wheat crops.  

Orange Juice is currently trading towards the upper side of a two-year range. A sustained move above $140 would suggest a return to medium-term demand dominance. 

Wheat exhibits a short-term oversold condition and posted an upward dynamic on Friday. However, it did not follow through to the upside today. Nevertheless, a reversionary rally back up towards the 200-day MA is looking increasingly likely.