HEAT ADVISORY Click county for more information: Creek, Nowata, Osage, Pawnee, Rogers, Tulsa, Wagoner, Washington        

Hundreds gathered in the sunshine Saturday morning at the Oklahoma City National Memorial with one purpose: to remember.

The site, where 13 years ago the bombing of the Alfred P. Murrah Federal Building left 168 dead, has been transformed into a peaceful and serene outdoor tribute to the victims.

"We will never and must never forget what happened here," said Gov. Brad Henry during the ceremony.

At 9:02 a.m., the same moment the bomb went off years ago, the crowd observed 168 seconds of silence. In that moment on April 19, 1995, the "physical and psychological landscape" of Oklahoma City was changed forever, the governor said.

Oklahomans met the tragedy with triumph and resiliency, he said.

A symbol of triumph

Symbolic of that triumph and resiliency were the seedlings offered to families after the ceremony, each sprouted from the Survivor Tree, an American Elm that survived the bombing.

The outdoor memorial, green with spring, is a "remarkable, emotional place," said Bob Woodruff, who spoke during the ceremony. Woodruff, an ABC News correspondent, suffered a traumatic brain injury in 2006 while working in Iraq.

Seeing the site for the first time Saturday moved Woodruff to tears, he said.

The ceremony concluded with the names of each of the 168 victims being read.

Charlie Kaczorowski of Long Island first came to the memorial ceremony in 2005 for the 10th anniversary. The New Yorker assisted in the recovery effort after the 9/11 attacks and said that when he came to Oklahoma City, he felt as if he had found his "extended family."

He returns each year to be with that "family" and to see "the most beautiful memorial in the world."

Bettie Lewis — whose daughter, Charlotte Andrea Lewis Thomas, was killed in the Social Security Administration office on the first floor of the federal building — said the ceremony is important to show the victims haven't been forgotten.

Lewis said she has attended the ceremony every year and "wouldn't miss it." She came Saturday with several family members, all wearing giant buttons bearing images of Charlotte's face.

"Lives have changed forever, but we still remember," Lewis said. "Thirteen years later, we still remember."