Both the Flower Show and Odunde are rain-or-shine events.

This is not the stuff of the organizers’ dreams: Thunderstorms Sunday could interrupt both the Philadelphia Flower Show and the Odunde Festival, two of the city’s largest annual outdoor events.

The government’s Storm Prediction Center has Philly and most of Eastern Pennsylvania under a “slight risk” for severe weather, defined as storms with winds approaching 60 mph. “Large hail” also is possible, the National Weather Service Office in Mount Holly said Saturday night.

The best chances for thunderstorms would be around the Flower Show’s opening and closing times, 10 a.m. and 6 p.m., Ray Martin, a weather service lead meteorologist.

» READ MORE: Odunde returns after a two-year hiatus

Odunde, which organizers say is the largest African-American festival in the country, kicks off with a procession at noon across the South Street Bridge, and what the atmosphere will be doing at that time is very much up in the air, Martin said.

“It’s pretty uncertain,” he said, citing conflicting advice from computer models. “The guidance is all over the place.” He said he couldn’t rule out midday showers.

If you like certainty with your atmosphere, be advised that you are probably in the wrong time of the year, if not the wrong part of the planet.

“I’ve been monitoring the weather all week,” said Barbara Grant, spokesperson for Odunde, which began in 1975 and is returning after a two-year hiatus.

Odunde, spread over 15 blocks in the Graduate Hospital area, is a rain or shine event, as is the Flower Show.

Flower Show organizer, the Pennsylvania Horticultural Society, is promising a 100% chance of flowers for the annual gala, which continues through June 19, and for the second year is being held outdoors at FDR Park in South Philadelphia.

» READ MORE: Your guide to the Flower Show

Last year’s outdoor inaugural had its weather hiccups, and 2022 showgoers may experience unwelcome encores. However, if conditions in the upper atmosphere align properly, there could be a pleasant run of days for strolling among the 15 acres of floral displays for the duration of the show.

At the 2021 show, a nasty thunderstorm forced a premature closing on the fourth day of the event, and organizers took some heat for their no-refund policy. And speaking of heat, temperatures were in the 90s on the first three days.

This time around, no 90-or-better readings are in the outlook through Juneteenth, for now anyway, and certainly not during this weekend when they might not get past 80.

Monday, Tuesday, and Wednesday are expected to be well-behaved June days with highs in the mid-80s, but shower chances return Thursday and Friday. It wouldn’t hurt to pack an umbrella or poncho.

» READ MORE: This year's Flower Show theme is "In Full Bloom"

This time of year with heat energy increasing and the atmosphere ever more languid and capricious, “it’s harder to guarantee a dry day,” said Paul Walker, senior meteorologist with AccuWeather Inc. “It’s hard to time anything.”

Even in the pre-COVID days when the event was held indoors at the Convention Center, weather was an issue.

Historically, the Flower Show was held in March, and it seemed to have some particularly bad luck.

On March 13, 1993, a “Storm of the Century” blizzard shut down the show on the closing weekend.

» READ MORE: In 2018, what a weather week that was

Eight years later, the event was bedeviled by the forecast of a Storm of the Century sequel that didn’t materialize. In 2018, a potent nor’easter on the eve of the opener, and a powerful sequel in the middle of the week, layered heavy, wet snow upon the region, but didn’t shut down the show nor discourage the crowds.

In any event, snow won’t be a problem this year.

Rain won’t close the show, only severe weather or lightning. “We need at least 30 minutes following lightning on the show grounds to reopen,” said flower show spokesperson Grace Savage. At that point a decision would be made whether enough time was left in the day to grant re-entry, she added.

Odunde will go on, Grant said, adding that she is hoping any showers would be short-lived, as is often the case this time of year.

As for the Flower Show, the FDR site has few covered areas, and the organizers recommend bringing rain gear. If guests have to evacuate, the tickets would be good another day.

Showgoers can purchase insurance or an “any day” ticket for an extra $5, which gives you the option to choose to attend any day between the 11th and 19th.

If it does rain, just remember, all those things you are admiring love this stuff.