The CME Group grains are hanging on to slim gains in early trading Thursday.

March corn is trading 1/2 cent higher at $6.17 per bushel, while March wheat is 1 1/2 higher at $6.18 1/2 and January soybeans are 5 1/4 higher at $11.59, according to Barchart.com.

• See all the latest grain futures prices

Some see the slip in market gains continuing through this week, the end of which could see positioning ahead of the long holiday weekend. Market analyst John Roach with Roach Ag Marketing, Ltd., issued sell signals for both corn and soybeans Thursday morning. But, does that mean the wheels have fallen off the rally bus?

"I bet the market retracts into tomorrow and it could be a place to lift hedges or buy in preparation of a rally starting next Tuesday," says Agriculture.com Marketing Talk contributor mspencerfarms.

In the background continues the South American weather pressure situation. Marketing Talk member agmr said Thursday morning almost 2/3 of the Brazilian corn crop and just shy of 45% of its soybeans are "susceptible to weather losses," especially with growing prospects for a repeat of a strong La Nina system in the coming months, one that typically means more heat and dryness in the southern hemisphere.

• Read more: Worst is yet to come from La Nina
  
• Slideshow: How much rain in South America?