It's a safe bet that it will rain sometime during the 10 days of the Three Rivers Arts Festival, which begins Friday. It does every year.
And as surely as April showers bring May flowers, early June showers will revive the popular Pittsburgh myth that the arts festival brings unusual downpours.
That's right -- myth.
For the second time in three years, we plunged headfirst into a reservoir of weather data to determine whether the equation "arts festival equals rain" holds water.
This time we looked at the last eight years, and what we found was that it rained on 38 of the 101 arts festival event days, or 37.6 percent. For the entire month of June in those eight years, it rained 103 of 240 days, or 42.9 percent. So arts festival days were more likely to be rain-free than the rest of the month.
The total June rainfall for our eight-year study period was 31.84 inches. Of that, 8.49 inches, or 26.7 percent, fell during the Downtown arts festival. Formerly a 17-day event and now 10 days, the arts festival occupied 42.1 percent of June during those eight years, meaning not only did it rain on fewer days, it rained less.
One last statistic for those not already numb: For the 30 years from 1981-2010 for which the National Weather Service has posted data, it rained here an average of 151.2 days per year, or about 41 percent. So the arts festival has not only been drier than the rest of June; it's drier than the yearly average.
One reason the arts festival cops a bad rap for weather is that June is the wettest month in Pittsburgh, with average rainfall of 4.3 inches.
Another is that it always rains at some point in the festival, causing chatter in elevators and at water coolers about how "it's raining, the arts festival must be here."
Two years ago, when we published our scientific findings on the first day of that year's festival, it promptly rained.
This year, the festival will open to sunny skies and temperatures in the mid-70s on Friday and more sun and a high near 80 on Saturday. Showers and thunderstorms are possible on Sunday and Monday, according to the National Weather Service.
And when the skies inevitably open, an urban legend will endure.
Jon Schmitz: firstname.lastname@example.org or 412-263-1868.