Kevin Johnson, Natalie DiBlasio, and Aamer Madhani

USA TODAY

PHILADELPHIA -- They came to call for an end to deportation centers and support for immigrants. They came mostly to support former presidential candidate Bernie Sanders, while deriding the Democratic National Committee after e-mail leaks showed officials apparently trying to sabotage Sanders' campaign.

For and against a constellation of causes, hundreds peacefully streamed down the city's main thoroughfare from City Hall, where the only threat to public safety was the stifling heat on the opening day of the Democratic National Convention, with temperatures hovering near 100 degrees and the heat index reaching 109 by late afternoon.

Later in the evening, the heat was broken by violent thunderstorms accompanied by high winds, which caused giant tents to sway outside the convention headquarters at Wells Fargo Center and sent protesters scattering for cover. The tents, constructed to house a massive contingent of media organizations, rumbled but did not buckle.

Lightening and heavy rains rolled in just as Green Party presidential candidate Jill Stein was set to address several hundred demonstrators at a protest near the convention hall.

The weather forced Stein to cut her remarks short but not before she told the crowd to dismiss Democrats who say it's their duty to vote for Clinton for the sake of stopping Trump.

"Forget the lesser evil, vote for the greater good, " Stein said.

Samantha Phillips, the city's emergency operations director, said the unsettled weather and intense heat could last through the end of the week.

Police reported no arrests late Monday, although 55 people were issued citations for disorderly conduct, officials said. Though the series of protests drew substantial numbers, the groups appeared to register only a fraction of the 50,000 per day that city officials estimated prior to the convention opening.

Police Commissioner Richard Ross, who spent much of the morning in the streets near City Hall, described the demonstrations as largely "very peaceful.''

"It is going well so far," Ross said. "Police are out there doing their jobs and even getting accolades from some of the protesters."

The friendly interactions between activists and police largely mirrored the street scene last week in Cleveland, which hosted the Republican National Convention without major incident.

Final tally: Just 24 convention-related arrests in Cleveland

Like Cleveland, Philadelphia police were making heavy use of bike patrol officers to guide protesters on marches through the heart of the busy downtown.

Ross said the only major concern appeared to be the oppressive heat, as officers and other city officials paid close attention to the well-being of protesters by distributing water and checking on elderly demonstrators during their long marches -- about three miles -- down Broad Street to the city's FDR Park adjacent to the convention headquarters and Wells Fargo Center..

At one point Monday, activists engaged in a brief sit-in along the march route, demanding that the Mississippi flag, which includes the stars and bars of the confederacy, be removed from a street display of all state flags.

City authorities removed the banner by late afternoon, saying it had been the subject of dozens of complaints prior to the convention.

Brian Abernathy, the city's first deputy manager, said the flag was being removed indefinitely, not just for the run of the convention.

Expect heavy security at DNC in Philadelphia

Demanding equality

The day started early for a group of about 100 people who gathered outside City Hall to rally on behalf of the Equality Coalition, many carrying placards supporting Sanders or slamming the Democratic National Committee. By mid-day, the group's numbers had swelled to several hundred.

Cory James, 22, of Flint, Mich., said that while he hadn't yet given up hope that Sanders could pull a convention "surprise," he said he could never vote for presumptive nominee Hillary Clinton.

"The Democratic Party doesn't represent me anymore," James said. "It represents corporate interests, that's all."

Joel Bradshaw, 39, bused down from New York on Friday carrying his "Bernie flag," anxious to lend his voice to the downtown demonstration.

"If Hillary wants to be queen, we'll bring the guillotine," he said.

Bradshaw said he was not advocating violence, only a "loud voice."

Almost as soon as the Equality Coalition left City Hall on its long march down Broad Street, another large group took its place.

A mix of Sanders supporters, opponents of the U.S. drug war and anti-media activists, the crowd joined in a thunderous chant of "Feel the Bern!" At one point their voices drowned out traffic cop whistles and car horns along the busy traffic circle.

A demonstration "concession" wagon was being pulled through crowd offering protesters free peanut butter and jelly sandwiches, bagels, peaches and water.

Amnesty International spokesman Eric Ferrero said groups of observers have been dispatched with the marchers, who he described as "peaceful" for the length of the route.

Young entrepreneur

Amadou Magassa, 13, of Philadelphia, sold water and Gatorade on Broad Street in anticipation of the protest. He said he came up with the sign idea: "Democrats $1, Republicans $10 - just kidding, everyone needs to hydrate today!" because of the convention.

Sales have been great, he said, wiping sweat off of his face. As the protest passed, Amadou estimated he sold 40 bottles. Only three remained.

Why is he out in 97-degree heat?

"My mom says I have to save up for college."

Message of love

As police choppers hovered overhead and emergency vehicles whizzed by with sirens blaring, David Seacord parked his bike at Washington and Broad streets, just ahead of a few hundred protesters making their way south toward FDR park.

The 68-year-old Oregon native drove from the West Coast to spread his message of love, which he usually preaches at music festivals. But after a close call driving down a slick Oregon road a few weeks ago, where his trailer began to fishtail, Seacord said he felt compelled to take his message to a bigger stage -- the DNC -- to counter balance a campaign season marred by insults, fear mongering and hatred.

An enthusiastic Sanders supporter, Seacord complained of the economic and power imbalance he sees in this country.

"These marches are being held by people who have thrown off concern for political repercussions," He said. "The house of cards is falling down."

Seacord said he believes Hilary Clinton and the Democratic establishment are too concerned with self-interest.

"The Democratic Party has two days to get its act together," Seacord said. "They better not walk down the aisle."

Immigration rally

Angel Mendoza came from Texas to an immigration rally that drew about 100 people. To get their votes, they said, the DNC must consider policies to shut down the deportation centers and help immigrants.

Growing up in El Paso, Texas, Mendoza regularly witnessed families who came to the U.S. from Mexico.

“The deportation centers are absolutely dis-respectable, they are keeping children, and they have cases where they were sick and didn’t get any sort of medical attention," he said. "They separate the women and the children and they keep people from even talking to them and seeing them from inside.”

“This is still my family even though we are not blood related," he continued. "We have the same skin color, we have the same history, we have the same culture, we have the same language."

Indict DNC

Roseanne Ferrara, holding a parasol in one hand and an "Indict DNC Election Fraud" sign in the other, echoed President Barack Obama's 2008 campaign "fired up, ready to go" refrain as she warmed a few hundred protesters at the city hall demonstration.

Ferrara is a lifelong Democrat, but she said she refuses to back Clinton. She wants to see Sanders run as a third-party candidate if super delegates don't shift their votes and give Sanders the nomination this week.

"All of us are fired up and ready to go...to take on the establishment," said Ferrara, of Asbury Park, N.J. "We are the people, and we are ready to be heard."

Not all the protesters are enamored with Sanders.

Andy Thayer, a liberal activist from Chicago who came to Philadelphia to protest against the Democratic Party, said the "Bernie or Bust" supporters are hanging on to a "pipe dream." He called Sanders a "Trojan Horse in the progressive movement."

Hundreds rally for Bernie Sanders in Philly heat

"He's a loyal Democrat and always will be a Democrat," said Thayer, who cited Sanders' backing of funding for the wars in Iraq and Afghanistan. "Our movements are strongest when they are opposed to both major parties."

Chalk-work

On the street just outside of Franklin Delano Roosevelt Park near Wells Fargo Arena, Holley Ohar, 43, of Jewett City, Conn., crouched to the ground to write "#StillSanders" in purple chalk.

"I am here to let the DNC know that even if they picked Hillary, we are not voting for her," Ohar said. "The people want Bernie."

Ohar's blue Bernie Sanders earrings jingled as she pulled her bright blue Bernie shirt over her head, drawing a cheer from a passerby as she adjusted her white Bernie Sanders hat.

"We are here to march for our lives," she said. "Bernie supporters are not just talk online. We are action - and we are here, missing work, missing everything - to prove that."

-- With reporting from Iris Ouyang, Thomas Vogel, Grant Miller and Raquel Zaldivar.