Death toll passes 140 in Joplin, Mo.

>>> where they are still trying to reconcile who lived and who died from last weekend's powerful tornado, the death toll grew again today to at least 142, with a significant number of people still unaccounted for. with ten more victims found, including a teenager swept away just hours after his high school graduation, this is now the deadliest tornado season in the u.s. since 1947 . at least 522 tornado deaths this year, from the upper midwest to the deep south . nbc's ron allen remains in joplin tonight for us and joins us right now with the latest. ron?

>> reporter: good evening to you, lester. today town officials here said that the water is now safe to drink. and power has been restored to most parts of the city that are still standing but they are still counting their losses. about 100 people are still considered missing. some families still don't have a good idea of exactly what happened to their loved ones . somewhere in this rubble is the house where malisa crosby lived. her sister lindsay malina has been everywhere with this cell phone picture, telling how neighbors found crosley laying on her 9-year-old son, who survived with severe irnlgz. molina thinks her sister's body was taken to the morgue but she doesn't know for sure.

>> we have comfort in the fact we know her last task on earth was to be a mother and protect her son.

>> reporter: notifying families has become such a sensitive issue missouri's governor has asked forensic teams to work around the clock. but about 90 sets of remains have not been identified.

>> it is our hope that with this accurate, respectful information that healing and mourning can begin.

>> it is past but i understand there's a lot of victims here.

>> reporter: will norton's family just got the news they did not want to hear.

>> i thank all of you for supporting us and remember there are so many more people out there and people that need your help.

>> reporter: they'd searched day and night since the tornado snatched the 18-year-old from his car on the drive home from his high school graduation. his body was found late friday in a pond. it is an emotional holiday weekend of tributes to loved ones lost in the storm. m. dean wells , 59, remembered for helping others survive the rubble of the home depot store, where he worked and perished.

>> your teams are ready to go.

>> reporter: through it all, help keeps coming. armies of volunteers from across the country.

>> i feel so much sympathy for these families. i can't imagine. you know, i complain about gas prices . and here they are, you know, they have nothing.

>> reporter: the main mission for this group, 2,000 strong? work through mountains of debris, helping joplin 's survivors salvage as much as they can of their lives.

>> i've never seen anything like this my entire life, and i know i probably never will. it's just terribly shocking.

>> reporter: tomorrow there will be a moment of silence here at 5:41 p.m ., the exact moment one week later after the tornado struck. that follows a memorial service . president obama will be here as well to see this destruction, to meet with families and first responders, and to offer the thoughts and prayers of the entire nation. lester?

>> ron allen in joplin for