NEW YORK — Dark clouds no longer dominate the NFL horizon. Rays of sunshine have broken through as owners and players make progress in labor talks.

So what could cause rain to fall, washing away the chance of a deal?

Plenty.

“Much can still go wrong — every negotiating session is unique to itself,” says Don Yee, who represents Tom Brady and is an adjunct law professor at Southern California. “Just because one day was good doesn’t mean the next day will be, too.”

How good those days have been also is relative. Although meetings in Chicago, New York and, most recently in Maryland have been productive, they have not created enough common ground for either side to declare a breakthrough is imminent. The owners have their own meetings in Chicago on Tuesday, with a possibility they will stick around through Wednesday to discuss the many topics being negotiated, from the percentage of total revenues offered the players to a rookie wage scale to parameters for free agency.

There’s even a chance a framework for a new collective bargaining agreement could be presented to them.

Yet it all could come crashing down in this fourth month of the lockout.

“More than the business points, two things will impact the final outcome: the ability of the participants to moderate their egos, and the actual drafting of specific language to fit the concepts being discussed,” Yee said. “The language of the last CBA gave rise to many grievances, which was fairly predictable as every lawyer tries to inject an edge for their client in the language. This will be a significant area of contention.”

Also potentially contentious is the ownership dynamic currently in place. The league wisely has included such hard-liners as Cowboys owner Jerry Jones and Panthers owner Jerry Richardson in all significant negotiations, along with moderates — and dealmakers — John Mara of the Giants and Robert Kraft of the Patriots. But there’s a wide split in team values and opportunities for outside income. Small-market owners such as Buffalo’s Ralph Wilson, Jacksonville’s Wayne Weaver and Cincinnati’s Mike Brown won’t approve any deal that doesn’t protect their interests.

A new CBA will require 24 of the 32 owners voting yes, and while Mara, Kraft, Art Rooney of Pittsburgh, and NFL Commissioner Roger Goodell can be very persuasive, there surely are more than eight owners who feel burned by the 2006 agreement. The owners opted out of that CBA in 2008.

There’s also the potential for a power play by one side or the other.

“A deal is far from over and until there is agreement on everything there is agreement on nothing,” says Marc Ganis, president of Chicago-based sports business consulting firm Sportscorp Ltd., and a keen observer of the league’s business side, “the greatest risk to a deal getting done and playing the entire 2011 season is if one party or the other grossly overplays their hand. It’s possible, more from the players’ side because there has been more emotion, pride and hyperbole during this process from their side. But the owners could also overplay their hand.”

Also worth considering: How can each side come out a winner? Initially, at least, both the owners and the players had elements they could brag about in the latest CBA.

But what if one side gets greedy?

“Nibbling,” attorney and player agent Ralph Cindrich, calls it. “Reaching an agreement and then adding one more thing. In my view this is unethical when it occurs. Careful negotiators close it completely and allow nothing in from the point of understanding.”