During NFL games in which snow has accumulated on the field of play, teams are allowed to clear some parts of the field based on guidelines set by the game operations manual set out by the NFL.
Teams/officials/field crew are able to clear the sidelines, goal lines and end lines to ensure clear indication of down yardage, scoring, etc. During a drive, are allowed to clear the 10-yard stripes behind the offense, not in front of the offense. During the play and during timeouts, the only thing teams can clear in front of the offense is the goal line if the referee deems that the goal line is not visible. No artificial tools are allowed to be used to clear the field to the benefit of a team.
Additionally, if the offense is inside the 20, teams can't clean the 5-yard stripe directly behind the offense because it might end up benefiting a field goal attempt in an area that's clean, so therefore, that's not allowable. The kicker and holder can't use anything like a brush to clear the spot of where they are going to attempt a field goal, but they can scrape off the snow with their hands or feet.
However, these rules aren't set in stone and may see some violations as officials on the field can make judgement calls as to the weather and the fairness of the situation.