By: Terence Burlij and Christina Bellantoni

Flipped vehicles are piled up outside the heavily damaged Moore Medical Center after a powerful tornado ripped through the area on Monday in Moore, Oklahoma. Photo by Brett Deering/Getty Images

A massive tornado ravaged a suburb of Oklahoma City on Monday, leveling buildings, killing at least 51 people, and temporarily brushing aside a trio of brewing political storms that had been the focus of official Washington in recent weeks.

President Barack Obama will receive a briefing from senior members of the administration's response team prior to delivering a 10 a.m. ET statement on the Sooner State rescue and recovery efforts from the White House State Dining Room. (Mr. Obama's original schedule had a series of closed meetings, including one with people affected by immigration policy.)

Watch the president's remarks on the situation in Oklahoma here.

At the same time, a Senate Finance Committee hearing will get underway on Capitol Hill, where lawmakers will hear testimony from the ousted acting IRS commissioner and the former head of the agency who was in charge during the period agents were targeting conservative groups that had applied for tax-exempt status.

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By: Associated Press

Television footage shows the massive funnel cloud that moved across the suburbs of Oklahoma City Monday.

Update 11:48 p.m. President Obama signed a disaster declaration for Oklahoma, minutes ago.

BREAKING: President Barack Obama declares major disaster in Oklahoma after devastating tornado

— The Associated Press (@AP) May 21, 2013

Update 11:28 p.m. | The following AP video shows survivors being pulled from the debris and loaded into waiting ambulances.

Update 11:03 p.m. | Oklahoma Governor Mary Fallin and city officials held a press conference earlier this evening. Fallin said that Oklahoma had received offers for resources from governors from other states across the nation, as well as from President Obama. She added that for now, downed power lines, blocked roadways, and overloaded telephone networks were hindering the emergency response.

The Associated Press has published a set of maps and graphics showing the path of destruction in Oklahoma, the latest information about the number of people killed or injured in the storm, and some background information on tornadoes.

Update 10:19 p.m. | Earlier today, the National Weather Service provided these details on the tornado:

Newcastle-Moore OKC Tornado was on the ground approx. 40 minutes. Tornado warning was in effect for 16 minutes before tornado developed.

— NWS Norman (@NWSNorman) May 20, 2013

Update 9:16 p.m. | AP has tweeted that the state medical examiner's office is now reporting 51 killed in the Oklahoma tornado, with children among the dead.

BREAKING: State medical examiner's office: 51 killed in Oklahoma tornado, with children among the dead -RJJ

— The Associated Press (@AP) May 21, 2013

Update 8:55 p.m. | There are at least 37 people reported killed. Authorities expected the death toll to rise as emergency crews moved deeper into the hardest-hit areas. At least 60 people were reported hurt, including more than a dozen children.

Update 7:02 p.m. | The Associated Press is following the story in Moore, Okla., where the twister touched down. Follow their updates via Twitter:

BREAKING: Several children pulled out of rubble alive at Plaza Towers Elementary School in Moore, Okla. -RJJ

— The Associated Press (@AP) May 20, 2013

Update 6:17 p.m. | The National Weather Service says the tornado that hit Moore had wind speeds up to 200 mph. The weather service's preliminary classification of Monday afternoon's tornado was an EF-4 on the enhanced Fujita scale.

Update 5:30 p.m. | Authorities also report that an elementary school in the area took a direct hit from the twister.

Gary Knight with the Oklahoma City Police Department says the school suffered "extensive damage."

Update 5:05 p.m. EDT | The Associated Press is reporting that a mile-wide tornado has ripped through suburban Oklahoma City Monday afternoon.

Video showed homes and buildings in Moore, Okla., were reduced to rubble, and vehicles littered roadways south and southwest of Oklahoma City.

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More:

• Live updates from NPR member station KGOU in Oklahoma.

• Live updates from The Oklahoman, including a map of the twister's path and video from the scene.

• Follow the tweets from the National Weather Service in Norman, Okla.

By: Meena Ganesan and david coles

Photo illustration by PBS NewsHour created with Pic Stich

Yahoo, the languishing tech pioneer, officially unveiled its acquisition of social blogging platform Tumblr on Monday. The $1.1 billion purchase by Yahoo could mean a whole world of things for both of the Internet companies, as well as for Yahoo chief executive -- and former Google executive -- Marissa Mayer.

We spoke with Rebecca Lieb, a research analyst of digital advertising and media for the Altimeter Group and Steven Levy, a writer for Wired, about the deal and Yahoo's strategy behind it.

Where does Tumblr fit into the Yahoo strategy?

There are handful of things Yahoo wants from this buy, according Rebecca Lieb, a research analyst of digital advertising and media for the Altimeter Group. They want to vastly expand the Yahoo audience, Lieb told the PBS NewsHour. "Not just eyeballs, but expanding into a demographic, the millennials, the 20-somethings."

Yahoo was once a relevant Internet body, Lieb said:

It very badly needs to re-invent itself, to be, if not cool at least relevant again ... And Tumblr brings an elusive component of coolness. One of Mayer's big challenges is keeping it cool when it is owned by a less cool corporate entity.

Steven Levy, a writer for Wired, dubs Tumblr an "image-enhancer" for Yahoo. Tumblr provides Yahoo with a way to increase its content output by repurposing user-generated material, Levy said, adding that the site elevates a platform already loved by so many people. "The technological success for Tumblr, and now Yahoo, will be teasing content out of people for free."

What does the Tumblr experience say about the future role of mobile?

Lieb said that mobile is increasingly about imagery and cites Facebook's revamp and focus on images after its acquisition of the social photo sharing tool Instagram. "A picture is worth a thousand words," she said. "People don't type about their dinner. They upload photos." Yahoo's pick-up of Tumblr could mean even more change in the future of Yahoo's mobile strategy visually.

While Yahoo has seen significant plays on mobile, Lieb said the company, along with Facebook and Google, has yet to find the winning formula yet. "No one has won," she said. "The battle is just beginning."

Why was there negative reaction among Tumblr users?

"Tumblr has a very indie feel to it," said Levy of what some have called the "hipster blogging service."

The idea of a conglomerate led by a former Gooogler taking hold of that content, he added, could be disturbing. The social website revolt is a familiar tale. You can see some of those reactions here.

Levy also noted that pre-Melissa Mayer, the Web pioneer had a "miserable reputation of taking on new companies and doing nothing with them." (Note Yahoo's 2005 acquisitions of Flickr and del.icio.us.)

Is there any way to tell how difficult it will be for Yahoo to make money with Tumblr?

"The model Yahoo doesn't want you to look at is NewsCorp buying Myspace, and the model they want you to look at is Google buying YouTube," said Levy. The strategy there? "Google made the smart decision to not call YouTube Google Video."

On Yahoo's newfound relationship with Tumblr, Lieb's advice is to be hands-off and leave it alone. "If Yahoo goes in and makes radical changes, the audience will defect." But Yahoo can build Tumblr's advertising model, Lieb said. "At the same time, Tumblr will bring a new form of non-advertising," or native content marketing to Yahoo.

Content marketing is less alienating to the young millennial audience Yahoo is courting, signaled in this acquisition, said Lieb.

Are these tech sector deals still running ahead of their real value or are they starting to calm down?

While the jury's still out on the $1 billion Facebook-Instagram deal, YouTube surely helped Google, both Lieb and Levy agree. But these acquisitions are not the type that are expected to break even by the next quarter or even by the end of the next fiscal year, said Lieb.

"Generally these mergers don't work," said Levy, noting that for every Google success met by companies like Android and YouTube, there are ten other companies that acquired and had failures.

Watch Monday's NewsHour for more on the blockbuster merger.

By: Cat Wise

Spencer Michels sat down with Alex Pandel and Eddie Tejeda, two of the co-founders of an app called BlightStatus, as part of Code for America's fellowship program.

"Government is supposed to be about how we do things together and we can do that much more together if we use technology smartly right now." Those are the words, and guiding philosophy, of Jennifer Pahlka, founder of the San Francisco nonprofit startup Code for America. Code as in computer code. The organization connects technology professionals, like web programmers, to cities around the country that are looking for innovative ways to address specific problems in their communities.

Tech experts embedded in the cities are part of Code for America's one-year paid fellowship program, which has been dubbed "Peace Corps for geeks." In just its third year, Code for America is gaining attention; more than 500 people applied for 27 fellowship spots this year. Some come from well-known Silicon Valley companies like Apple, Yahoo and Google. Those who are chosen receive $35,000 for the year, a sizable pay cut for many applicants.

Teams of fellows spend a month in the city they are assigned to work with, listening to officials and residents explain their specific challenge -- like improving food distribution to low-income residents, or improving municipal transportation information. The teams then return to Code for America's headquarters to develop a web-based program they think will help.

A number of small-scale but interesting apps have come out of the collaborations so far, like Adopt a Fire Hydrant in Boston and BlightStatus in New Orleans. You can see a list of other Code for America projects here.

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By: Larisa Epatko

President Obama and Myanmar's President Thein Sein in Yangon on Nov. 19, 2012. Photo by Jason Reed/Reuters.

Myanmar President Thein Sein becomes the first leader of Myanmar, formerly known as Burma, to visit the White House in 47 years on Monday. Their meeting is viewed as an affirmation of the Southeast Asian nation's democratic transition.

The last White House visit was by the late Burmese dictator Ne Win in 1966 during the Vietnam War.

Thein Sein's visit comes after President Barack Obama traveled to Myanmar in November, becoming the first sitting U.S. president to do so, in a further sign of warming relations. "We've reached a point in our relationship where (Thein Sein) is received in Washington. That's a big deal," said Priscilla Clapp, who headed the U.S. Embassy in Burma between 1999 and 2002.

A statement from the White House referred to the country as "Myanmar" -- the current government's preference -- rather than Burma, and described U.S. support:

"The president looks forward to discussing with President Thein Sein the many remaining challenges to efforts to develop democracy, address communal and ethnic tensions, and bring economic opportunity to the people of his country, and to exploring how the United States can help."

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By: Laurence Kotlikoff

Fifty-two percent of women over 60 aren't married and nearly 70 percent of those over 75. What Social Security benefits are they entitled to? And what about single or divorced men? Photo by Jim McGuire via Getty Images.

Larry Kotlikoff's Social Security original 34 "secrets", his additional secrets, his Social Security "mistakes" and his Social Security gotchas have prompted so many of you to write in that we now feature "Ask Larry" every Monday.

We are determined to continue it until the queries stop or we run through the particular problems of all 78 million Baby Boomers, whichever comes first. Kotlikoff's state-of-the-art retirement software is available, for free, in its "basic" version. His considerable and often very useful output is available on his website.

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A. Price: One or two of us Americans are single or divorced [and we are also] eligible for Social Security benefits now or in the near future. Are you ever going to address the questions of this "fringe" population?

Larry Kotlikoff: Glad you asked. I've addressed Social Security's treatment of singles, but you're right. Questions about married couples have taken up most of the space.

Older America's single population is, in fact, anything but "fringe." Some 30 percent of males and 52 percent of females over 60 aren't married. Past age 75, the number increases to almost 70 percent of females not married, the majority of them widowed.

These figures also tell us that many currently "non-fringe" married people, particularly women, are likely to end up on the fringe. Hence, it's important for almost everyone to understand Social Security's treatment of single people and how single people can take Social Security's best deal.

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By: Miles O'Brien

American astronaut Sally Ride monitors control panels from the pilot's chair on the flight deck in 1983. Photo by Apic/Getty Images.

*Editor's note: On Monday, PBS NewsHour science correspondent Miles O'Brien will serve as master of ceremonies at an event honoring the legacy of astronaut Sally Ride at Washington, D.C.'s John F. Kennedy Center for the Performing Arts. Monday's tribute will highlight both her impact on the space program as well as her lifelong commitment to promoting science literacy among young people. Through the organization she founded, Sally Ride Science, she reached out to young girls, encouraging them to enter careers in the Science, Technology, Engineering and Math (STEM) fields, where there is a noticeable gap.

NewsHour correspondent Jeff Brown spoke with O'Brien on Monday about Ride and her legacy:

And this is the column that O'Brien wrote immediately following Ride's death in July 2012, after a 17-month battle with pancreatic cancer.*

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On Jan. 28, 2003, I was sitting on top of the world -- and hoping that would soon be literally the case -- when Sally Ride knocked on my door in Atlanta. She was one of the guests of honor at my home that night to celebrate the opening of a new Challenger Learning Center.

It was no coincidence that this happened to be the 17th anniversary of the loss of OV-099 and the crew of STS-51-L. The surviving family members of that crew like to honor the last Challenger crew by cutting the ribbon on a new Challenger Center every year on January 28, if possible.

Sally was there to keynote the event at a museum (now defunct) called SciTrek, and I was hosting all the players involved in that noble cause.

Cheryl McNair, June Scobee Rodgers, Sally Ride and Miles O'Brien pictured at the opening of the Challenger Learning Center in Atlanta on Jan. 28, 2003. Photo by Ted Pio-roda/CNN.

When Sally arrived among this august crowd, she clearly owned the room. We all lined up for our photo with her, and she showed no impatience with what must have been for her a familiar ritual.

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By: Terence Burlij and Katelyn Polantz

Photo by Ann Hermes/The Christian Science Monitor via Getty Images

At this point, there appears to be more heat than light when it comes to discussion of the Internal Revenue Service's singling out of conservative groups for extra scrutiny when applying for tax-exempt status.

After a week of public statements of outrage, the release of a Treasury Department inspector general's report, the resignation of two IRS officials and the first congressional hearing on the matter, some guests on the Sunday talk shows still had much to say about it.

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By: Jenny Marder

A cicada perches on a leaf of grass at Virginia’s Bull Run Regional Park. The full brood of cicadas is expected to emerge en masse in late May or June. Photos by Jenny Marder.

After an afternoon hunting for cicadas on Thursday, I finally discovered a nice crop of them in a nest of poison ivy in Virgina’s Bull Run Regional Park. It took some scouring, but then there they were, with their veiny golden wings and bright beady red eyes, clinging to grass and leaves and tree bark.

And the signs of them were probably more visible than the creatures themselves. Their exoskeletons, which they shed after molting from nymphs into winged adults, littered the ground and tree trunks.

Their tunnels, especially, were everywhere you looked. A sign perhaps of many more to come?

The brood II cicadas are expected to emerge en masse in late May or June through these tunnels they’ve dug from under the earth to its surface. The nymphs have been living quietly underground for 17 years, sucking on plant roots.

I suspect this is only a preview to the possibly million cicadas per acre that science and history have promised us. The ones I found were docile and quiet — no sign yet of the hundred-decibel mating shrieks for which the U.S. East Coast is bracing.

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By: Paul Solman

The entrance at the 1912 Democratic National Convention held in Baltimore, Md. The theme of the presidential campaign of 1912 was economic inequality, but looking at the data, the problem is worse today than it was more than 100 years ago. Photo courtesy of the Library of Congress/Wikimedia Commons.

*Paul Solman answers questions from the NewsHour audience on business and economic news here on his Making Sense Business Desk page.

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Here's a question from Carolyn of Chicago, Ill., who writes:

"There is a lot of talk about income disparity between rich and poor today. How does it compare to the disparity 100 years ago?"

One hundred years ago? How about 101? Economic inequality is often cited as the key issue in the 1912 presidential election that pitted William Howard Taft (Republican) against Woodrow Wilson (Democrat), ex-Republican Theodore Roosevelt (Bull Moose Party), Eugene V. Debs (Socialist Party) and Eugene Chafin (Prohibition Party).

Roosevelt said around that time in a famous speech that the struggle for liberty "appears as the struggle of freemen to gain and hold the right of self-government as against the special interests, who twist the methods of free government into machinery for defeating the popular will. At every stage, and under all circumstances, the essence of the struggle is to equalize opportunity, destroy privilege and give to the life and citizenship of every individual the highest possible value both to himself and to the commonwealth."

Sitting President Taft said in a 1912 campaign speech: "Insofar as inequality of condition can be lessened and equality of opportunity can be promoted by improvement of our educational systems, the betterment of the laws to ensure the quick administration of justice, and by the prevention of the acquisition of privilege without just compensation ... all are in sympathy with the continued effort to remedy injustice and to aid the weak."

Unfortunately, when asked what he would do about high unemployment, he said "God knows." He ran third in the election.

Given these facts, it might be reasonably supposed that inequality a century ago was greater than it is today. Not so, however.

The most definitive published analysis I'm aware of measures the share of pre-tax income going to the top 1 percent of Americans from 1913 through 2008. It comes courtesy of economists Thomas Picketty and Emmanuel Saez and looks like this:

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