more local tonight, a massive school scare shutdown in los angeles. threats to new york and l.a. trigger the sudden closure of hundreds of southern california schools now being called a hoax. did l.a. officials overreact? is this the new normal after san bernardino? fight night in vegas. trump versus cruz. cruz versus rubio. and fireworks on the strip, as national security takes center stage. cancer. a new device that's prolonging lives. doctors calling it the most promising treatment for brain tumors in years. weather whiplash. record snow in the record heat in the east. businesses hit hard. and a major lawsuit over a hugely popular line of hair care products endorsed by celebrities, now hundreds of women say it severely damaged

right now. good evening, i'm kate snow. in for lester tonight. it's being called unprecedented, the massive shutdown of the second largest school district in the nation because of a credible serious threat of a large scale attack, or so it was first described. over 900 schools closed, searched room by room. hundreds of thousands of students affected. a chaotic day in los angeles. then we came to learn new york city received a similar threat. both now being called hoaxes. and new york's police commissioner says l.a. overreacted. but with the attacks in san bernardino still fresh in their mind, imagine being the official who has to make that call. migel almaguer has

>> reporter: shortly before 7:00 a.m., police were mobilized and the decision was made public. the nation's second largest school district saying it received a credible threat, abruptly shutting down all campuses just before the morning bell. >> they said that it wasn't no school due to a bomb threat. it's very scary. >> reporter: the unprecedented decision is what many woke up to. >> breaking news of the massive district-wide shutdown of lausd schools. >> reporter: the threat came by e-mail. a person claiming to be a high school senior ready with an army to attack schools with guns and bombs. los angeles is just 65 miles from san bernardino, where 14 were killed in a terror attack less than two weeks ago. >> i think the circumstances in the neighboring san bernardino, i think what has happened in the nation, i think

superintendent am not going to take the of a student. >> reporter: the police chief said the all los angeles schools. was explosive devices. the specific threat assault rifles and machine pistols. >> reporter: while the chief stood by, the superintendent, officials say they advised against closing schools, saying the decision was premature and a bad move. the coordinated sweep of l.a. schools for bombs a massive undertaking. lausd spans 710 square miles with more than a thousand campuses and 700,000 students, many about to take final exams. >> we have to live through this and live this way. trying to see if terrorists are going to come and get us. >> reporter: with school busses suddenly turned around, many had nowhere to go. staff and parents complained notification came too late. tonight, anthony karsen has to explain to his four-year-old son aj why fear has gripped the region and now his school.

like what's going on in the world, like with what happened in paris and san bernardino. he's just happy all the time. >> reporter: tonight law enforcement officials are still checking campuses for suspicious devices. meantime a 17-year-old student was struck and killed by a truck after he was crossing an intersection. it's unclear if that student was headed to or from campus after the school closures. kate? >> miguel, thanks so much. it appears a new normal is emerging after the attack in san bernardino, as a majority of americans now say terrorism is their number one concern. and with that as the backdrop, we saw a tale of two cities today, and the very different ways that new york and los angeles reacted when the threats came in. here's our justice correspondent pete williams on how it all went down. >> reporter: children in the nation's largest public school system in new york city headed to class today, even though police said a nearly identical threat was

new york's police commissioner said l.a. overreacted. >> it is not something we are concerned with. what we would be concerned with overreacting. we'll stay aware, we'll stay involved. but we at all costs cannot start overreacting. >> reporter: several law enforcement officials say the writer of both e-mails claimed to be a high school senior who was bullied and claimed to have an army of supporters who planted pressure cooker bombs and had assault rifles and pistols. the writer claimed to be a radical muslim but made mistakes in referring to islam, a phony threat, new york authorities concluded, because the same person could not be a student in two places at once. local and federal law enforcement officials say the l.a. schools chief made the decision and then consulted police, who officials say recommended against closing the schools. but there was a unanimous view about how serious the decision was. >> these are very high stakes.

making a decision about the color of a car or where we're going to eat for dinner here. these are -- this is the safety of our children. there is no more important decision. >> reporter: how to respond in an era of terrorism, and when schools have been the scenes of mass shootings, has become a huge challenge. >> schools are experiencing threats locally, from students, non-students, as well as s.w.a.t.-ing threats that send shock waves of panic throughout schools. >> reporter: investigators say syed farook might have been considering attacks on schools. tonight the fbi is trying to figure out who sent the threats. they've been sent to an e-mail service provider in the u.s. that's been popular with on line pranksters. >> pete williams in washington tonight,

it's fitting that national security take center stage as the candidates face off tonight in the final gop debate of the year. nbc's peter alexander reports a highly anticipated showdown is expected on the vegas strip. >> reporter: the republican candidates are bracing for a freewheeling and fiery slugfest in tonight's final debate of the year, the first with ted cruz at number 2, taking shots from donald trump. the heated campaign season boiling over as the trump show rolled into vegas overnight. >> we should have been doing that for the last seven years. i give him credit. >> reporter: trump's contentious rally repeatedly interrupted by protestors. several forcibly removed and heckled by audience members, one even yelling a nazi salute. >> seil heil! >> reporter: in the five weeks since the candidates last shared the stage, the world has changed. paris and san bernardino fueling new concerns about terrorism and national security, igniting debates over syrian refugees and trump's proposed temporary ban on muslims entering the u.s. >> you have the radical islamic extremists, they're

>> reporter: all of it reshaping the race, with contenders competing to show who is toughest. >> we will carpet bomb them into oblivion. >> a unique threat. it's not just foreigners coming into the u.s. it's home-grown extremists. >> reporter: that threat has exposed ben carson's lack of foreign policy experience, despite this statement posted to facebook today. >> i sure hope we get a lot of questions about foreign affairs and national defense. if so, slam dunk. >> reporter: once the establishment favorite jeb bush may be setting a record for futility, his campaign and super-pac spending millions of dollars in tv ads but still only posting single digit support. chris christie has visited las vegas 50 times since june, looking to impress a national audience. the impressions please candidates make may stick for a while. the next republican date isn't until the

just two weeks before the iowa caucus. back to you, kate. >> peter alexander out in vegas. as the republicans duke it out, democratic front runner hillary clinton detailed her own detailed her own plans for the white house late today, specifically her strategy for taking on isis. as nbc's andrea mitchell reports, clinton saved some of her toughest talk for the republicans taking aim at her tonight. >> reporter: with fear of another san bernardino or a paris-style attack in the u.s., now a top worry for americans, hillary clinton took on donald trump and the republicans for their rhetoric, accusing them of becoming a tool for isis recruitment. >> promising to carpet bomb until the desert glows doesn't make you sound strong. it makes you sound like you're in over your head. >> reporter: her plan to stop isis: foil plots. enlist silicon valley to attack isis's online recruitment. empower muslim

front line. but while clinton likes to portray herself as a grown up -- >> bluster and bigotry are not credentials for becoming commander in chief. >> reporter: -- critics say she too is vulnerable for policies in iraq, libya, and syria that helped spawn isis, and for failing to help counter islamic propaganda online. plus russia's 11-week air campaign in syria has complicated u.s. plans. defense secretary ash carter visited u.s. pilots in turkey today, accused russia of bombing the anti-assad rebels, not isis. >> there are those not working in the right direction. obviously that includes russia. >> reporter: while john kerry in moscow tried to persuade vladimir putin that isis is now a threat to all of the civilized world. in a clear shot at president obama, hillary clinton also said it's not enough

obama once said. she said isis has to be defeated. >> andrea mitchell in washington. high drama in baltimore today. jurors in the trial of the first of the baltimore police officers charged in the death of freddie gray told a judge they were deadlocked and could not reach a verdict. but the judge sent them back to deliberate further. gray's neck was broken after he was arrested and put in the back of a police van earlier this year. his death of course triggering days of protests and civil unrest. officer william porter is charged with manslaughter, among other crimes. he faces up to 25 years in prison if convicted. another day of weather extremes across the nation. records are being shattered but in very different ways. on opposite sides of the country, record breaking snow in the west, and record breaking high temperatures here in the east. we'll hear more from nbc's dylan dreyer. >> reporter: this morning's commute in colorado a mess. hundreds of flights cancelled. the same storm dumped

in parts of montana. and in salt lake city, more than 9 inches fell, more than all of last winter. in the east, the other extreme. today, boston warmer than las vegas. and new york milder than phoenix. here in central park, we reached a record high of 68 degrees at 1:00 a.m. and it's not just new york city breaking records in the middle of the night. philadelphia hit 69 degrees. wilmington, delaware, 68. and providence, rhode island reached 64 by 4:00 a.m. the weather extremes all thanks to a strong el nio. >> although the seasonal forecast called for warmer than normal conditions through the winter for the northern u.s., that doesn't mean on any given day we can't have a cold outbreak and a winter storm. >> reporter: in vermont, 11 of the state's 50 ski resorts are open, a serious economic blow. >> christmas is a really important holiday for us and it's not looking so good. >> reporter: but for shoppers, warm temperatures are bringing the savings.

sale for 80% off. a change in the jetstream will bring cooler temperatures to the northeast this weekend. by next week, the warmth will be back, just in time for the first official day of winter. dylan dreyer, nbc news, new york. still ahead tonight, high tech hope for those diagnosed with brain cancer. the experimental device showing great promise that could give these patients something that want so badly -- more time. also celebrities swear by it on tv but now hundreds say a popular hair care line

effects. we're back with a promising advance in the battle against cancer. a device that uses electric waves to target the most aggressive type of brain cancer. tonight, we meet a woman who hopes it can buy her more time with the people she loves. nbc's janet shamlian has the first part of our special series of reports "target cancer: chasing a cure." >> reporter: amy has gotten used to her new headgear which she sometimes covers with a hat or wig. diagnosed with glioblastoma, she's trying a new treatment that a study out today finds is extending the lives of patients who have the deadliest form of brain cancer. it sends electric waves to the brain, preventing cancer cells from

it's worn almost round the clock and is used with surgery, radiation, and chemotherapy. it can't cure patients like amy. but the study shows it can add five precious months to their lives. >> this is the first clinical trial in a decade to lengthen the lives of patients with glioblastoma. so i think that this is going to be really exciting. >> reporter: glioblastoma is the most common form of brain cancer. doctors hope the device will extend the prognosis. >> we do expect now that it has been fda approved that the use will be more frequent and more widespread. >> this is always connected to the wires. >> reporter: amy has been wearing the cap and battery pack since october. it's doing its job while the 41-year-old does hers. >> you did your check, awesome. >> reporter: teaching math to middle schoolers in rochester, new york. >> i feel truly blessed that technology and treatments are growing

beat cancer. >> reporter: the device is expensive, as much as $20,000 a month. and yet priceless. prolonging life. >> the mri. >> reporter: after a devastating diagnosis. janet shamlian, nbc news, new york. >> tomorrow in our series we go inside los alamos to see how the top secret nuclear weapons lab came to the forefront of groundbreaking research that could change the fight against cancer. we're back in a moment with a state of emergency declared in one american city over a toxin.

children there. moving a tv is a real pain. would that be easier if i had prism tv from centurylink? sure. i've got centurylink's wireless set-top box, which makes it pretty easy. let me show you. i could move it here... or here... even here. switch to centurylink. get the prism essential tv package with internet for only $70 a month for one year with autopay enrollment. didn't even break a sweat. till just now. a state of emergency has been declared in flint, michigan, after high levels of lead were found in children's blood. the mayor calls it, quote, a man made disaster. he blames lead contamination in the water supply after a cost cutting decision last year to switch from using detroit's system to using the flint river.

reversed in october. people there are warned not to drink unfiltered tap water. a class action lawsuit has now been filed over a popular hair care line that so many people use. many you've seen those commercials on tv featuring celebrities for wen hair care. as stephanie gosk reports, hundreds now claim wen products have a startling side effect -- hair loss. >> reporter: the promises are bold. get beautiful, healthy hair with wen, created by hollywood stylist chaz dean. they say it's the best thing that has happened to their flowing locks. but hundreds of customers are alleging it's a nightmare. instead of flowing hair, their hair is falling out. a class action suit against the stylist and the marketing company accuses the company of not warning customers that the products contain an ingredient or combination of

significant hair loss. now testimonials like these are popping up. >> my hair is coming out. >> reporter: nbc news could not verify the claims. in a statement, the company says it will vigorously fight the allegations, writing in part, "there is no scientific evidence whatsoever to support any claim that our hair care products caused anyone to lose their hair. there are many reasons why individuals may lose their hair, all unrelated to wen hair care products." today both sides say they are working towards a settlement. >> let's face it. if you're having a bad hair day, it's a bad day. >> reporter: for wen and some of its customers, this may be the worst day imaginable. stephanie gosk, nbc news, new york. when we come back, a fond farewell to a retiring tv legend who has been a friend of

viewers. finally tonight, the end of an era here at nbc news, and for millions of viewers who have welcomed willard scott into their homes for decades on "the today show," delivering the weather and more than a few laughs, and so many birthday wishes. tonight we are wishing

sets off on a well-deserved retirement. nbc's harry smith looks back. >> good morning, willie. >> i'm singing to my jane while standing in the rain. >> reporter: willard scott was born to be a broadcaster. during 35 years on "the today show," he wore many hats and never failed to deliver a smile. at 16 he was an nbc page in washington, dc. we are the joy boys >> reporter: and became a partner in the best radio show there, and was even the first ronald mcdonald. then "the today show" called. >> willard scott joining the "today" family for the first time. >> reporter: overnight willard scott became a household name. during coffee or at the water cooler, america would say, "did you see what willard scott did today?" we watched willard have fun across the country and around the world.

representative for middle america on this program. i'm the kind of everyman. >> reporter: an everyman who could stop an inaugural parade. he could even stop a jogging president. >> could you believe this? >> reporter: and in the next breath wish happy birthday or happy anniversary to folks who had earned it. at "the today show," he was a friend to all and more than a mentor to al roker. >> if i had not had the blessing of meeting willard scott, then i wouldn't be doing this today. he's been like a father to me. >> reporter: this morning the "today" crew wished happy trails to their retiring friend. >> i'm going over yonder. >> where is yonder? >> over here. >> reporter: a weatherman, but a man for all seasons. harry smith, nbc, new york. >> wishing willard all the very best. that will do it for us on this tuesday night. i'm kate snow. for all of us at nbc

have a great night. and >> caught in the act. despicable reports a surface in a classroom. >> the playable spotlight is back on las vegas tonight as the republican presidential candidates have their >> easing concerns here at home. the constant worry of terrorist threats.