Memo to event planners everywhere: Don’t tempt fate by planning a high-profile gathering in the Loop this week.

We all know what happened to the NASCAR street race on Sunday, curbing its much feted, if controversial, trial run. The Grant Park Music Festival’s beloved annual Independence Day concert met a similarly watery fate on Wednesday. It had already begun storming by the time pianist Michelle Cann, one of last season’s most head-turning soloists, took the stage 30 minutes in for Gershwin’s “Rhapsody in Blue.” But Dario Brignoli had scarcely crowed out the piece’s iconic clarinet call when heavy rain pelted into Jay Pritzker Pavilion, forcing the “Rhapsody” to wrap up quickly. Even musicians tucked onstage got briefly drenched, with the festival’s Steinway concert grand taking a special soaking.

Following onstage guidance from festival President/CEO Paul Winberg, audiences who didn’t scatter into the night sloshed through ankle-deep water to take refuge in the Pavilion arcades. The concert was called off some 40 minutes later — mostly. More on that in a minute.

To think it started as a relatively quiet evening. Compared with other years, this summer’s Independence Day concert drew a slim crowd of about 4,500, many no doubt spooked by the foreboding forecast. The festival also remixed its usual tribute to veterans, trading the “Armed Forces Salute” of years past for Morton Gould’s wartime “American Salute” and a presentation by the Rickover Naval Academy color guard. (That apparently didn’t go over well with some attendees: Dale Taylor of evening sponsor AbelsonTaylor ribbed the festival in loose-cannon remarks.)

On the other hand, chorus director Christopher Bell’s star-spangled outfit was both sufficiently loud and true to Grant Park tradition: a bedazzled red jacket, blue stovepipe hat and garish American flag leggings that Bell, not reassuringly, said he hoped wouldn’t slip down while he conducted.

Typical, too, was an Independence Day array of repertoire both expected and offbeat. Bell and the festival orchestra progressed through Copland’s familiar “Variations on a Shaker Melody” more peppily than most, tossing off phrase ends with an appealing snap. If festival orchestra brass sounded unsure at the very top of the concert, in Joan Tower’s “Fanfare for the Uncommon Woman,” they whetted to a precise, decisive unit by the time Gould’s “Salute” came around, as if supercharged by the arriving lightning.

Just before rain stalled the concert completely, Grant Park’s appetite for novelties scrounged up a delicacy in “Chicago: Grande valse à l’américaine,” by Louisiana-born composer Edmond Dédé. As Bell noted in his audience comments, Dédé’s piece doesn’t have much of anything to do with Chicago — a city he never lived in — and indeed not much to do with America, either. But it is all frothy fun: “Chicago” shakes off a perturbed minor-key intro to become a carefree waltz, the requisite high-wire piccolo writing nicely handled by assistant principal flute Jennifer Lawson.

Now, for the dirty little secret most of Wednesday’s sopping attendees didn’t know: After the delay, the show did go on for the lucky few already seated in the choir loft onstage. The evening’s unplayed pieces were cut — catch you next year, “Stars and Stripes Forever” — but the festival closed the glass Pavilion windshield so Cann could at least see her “Rhapsody in Blue” through, ensconced from the murky blue tumult outside. So, Brignoli’s clarinet crowed again with the weird déjà vu of a second sunrise, and after a short orchestral introduction, Cann was off, driving through the very spot where the rain forced the festival’s retreat.

At that point, it didn’t mean a thing to call hers a memorable “Rhapsody.” Of course it was. But in any circumstance, Cann’s performance was transcendent and nourishing, burrowing into Gershwin’s score with equal parts relish and reverence. She played as if recounting a self-sustaining memory, her deft pedal work well-calibrated to the surprise setting.

The Grant Park Festival Orchestra met her ounce for ounce in passion, the lower strings smooth and mighty as a wind-shorn cliff and muted brass delighting with their froggy interjections in the latter half. Some gleeful audience members brought their outdoor attitude inside, cheering and whooping after solos. The only thing more explosive than the weather was the applause that came at the performance’s end.

Cann’s “Rhapsody” was a hard act to follow, but she had just the right bonbon up her sleeve: the late jazz pianist Hazel Scott’s virtuosic riff on Rachmaninoff’s Prelude in C-sharp minor. Scott’s version echoes the prelude’s solemn tolling chords before a total musical fake out, erupting into a playful stride number that kneaded in another C-sharp classic, Beethoven’s “Moonlight.”

You couldn’t possibly invent a better cap to the evening: harrowing storminess offset by a smile. Because at a certain point, you just have to laugh, don’t you?

Hannah Edgar is a freelance critic.

The Rubin Institute for Music Criticism helps fund our classical music coverage. The Chicago Tribune maintains editorial control over assignments and content.