Maybe it was the thunderstorm that burst above Merion just as the world's greatest golfer was planning to play a practice round.
Maybe it was the tornado watch issued mid-afternoon.
Maybe it was when USGA officials stocked the flooded bunker near the 11th green with trout.
Sometime Monday, the hosts of the 2013 U.S. Open experienced the helpless sinking feeling known well to anyone who has ever meticulously planned a major event — a wedding, a graduation party — only to have the weather dump all over it.
Years of preparations, millions of dollars spent to erect temporary buildings and miles of fencing — all of that, and then a tropical storm blows through, chased by bands of swollen gray clouds.
This is more than a mild inconvenience for spectators, although that is a very real concern, too. Rain that verges on biblical proportion saturates the course, a cruel trick of nature that changes the nature of golf itself.
"You're not going to see a firm U.S. Open this year," veteran Ernie Els said. "I'm sorry. I don't care if they get helicopters flying over the fairways, it's not going to dry up."
The way luck is running here, those helicopters would probably crash land in the quarry that distinguishes this old course.
A rain-soaked tournament can happen anywhere. Any course, softened by days of precipitation, can affect scores and strategies. But this is a unique situation. Merion had long been considered a charming and quirky but, frankly, outdated course for a major tournament. There was already real curiosity about how a course from Ben Hogan's era would handle the powerful athletes and vastly improved equipment of today.
The consensus seemed to be that it would take smarts and patience to master Merion and win the Open. That meant this could be the week that Tiger Woods, who has those qualities plus athletic prowess, finally wins his first major since 2008. It could also give Phil Mickelson his first U.S. Open title.
But that consensus was formed before the skies opened and dumped Lake Superior on the course. Lake Erie is expected to fall Thursday.
"Because of conditions," Els said, "(Merion) is not going to bare its teeth the way that it should. I know guys were hoping for a firm test. ... I see a very close race with a lot of players in contention this year, unlike other U.S. Opens."
So Merion is going to be judged not on its true merits — which would have been intriguing — but graded on a very soggy curve. It would be a shame if the USGA crossed the course, and other old-fashioned courses, off its list of possible host sites because of that.
But that's a matter for later. For this week, there's really only one way to handle the impact of the weather on the tournament.
The stage could be sloppily set for some unforgettable rounds of golf. Instead of tut-tutting the diminished challenge presented by soft and forgiving greens, relish the chance to see Woods, Mickelson, Rory McIlroy, Adam Scott and the rest post some crazy-low scores.
Weather has a way of making mundane events into legendary events. Without the rain, Woodstock would have been just a big traffic jam with a good soundtrack. Without the fog, the Eagles' 1988 playoff loss in Chicago would be indistinguishable from all their other playoff losses. Without the cold, the Ice Bowl would have been just another game.
The groundskeepers at Merion will do everything possible to get the course ready. It's not like Tiger's going to be knee-deep in muck (although it would be fun to see him mud wrestle Sergio Garcia on 11).
But the rough, already as unforgiving as any course's anywhere, will be especially wild. That will make it harder to recover from mistakes off the tee. The soft greens, on the other hand, will invite a little more risk on approach shots.
And the general evening out of the field — "It will be bunched," Els said — will push the best players even harder. There won't be any five-shot leads on Sunday. That should make for an exciting finish.
Really, that's all you can ask from any major tournament — even if the winner has to build an ark to get home when it's over.