Give Ross On Radio reader and frequent correspondent Steve Sobczuk credit for spotting it early. 

A month ago, the Waterloo, Ontario-based Sobczuk wrote, "There was a real R&B drought on top 40 for the better part of 2013, which doesn't make any sense after the big successes of 'Blurred Lines' and 'Get Lucky.'" After the worst stretch for R&B since the early '80s, he felt, "things really seem to be turning around with the breakout successes of Jason Derulo's 'Talk Dirty,' Pharrell Williams' 'Happy,' Kid Ink's 'Show Me' and Aloe Blacc's 'The Man.'"

Sobczuk's prediction came on the heels of headlines that no black artist had topped Billboard's Hot 100 in 2013 as a lead act. That was the inevitable consequence of a pipeline to pop radio that had seemingly dried up. Top 40 had long stopped looking to mainstream R&B/hip-hop stations for titles. Rhythmic had lost some of its agenda-setting power, and was picking up pop crossovers from mainstream. A few years ago, "Turbo-pop" had allowed Rihanna, Usher, and Chris Brown to have a separate body of hits at pop radio. In 2013, those slots went to superstar DJs (Zedd, Swedish House Mafia, etc.), and not R&B superstars.  

R&B hadn't entirely disappeared from pop radio, but the exceptions proved the rule. "Blurred Lines" happened only after Justin Timberlake started making the same sort of "grown and sexy" record that Thicke had been charting at R&B radio for nearly a decade. Drake scored one Hip-Hop hit after another but was welcome at top 40 only with his occasional ventures into R&B like "Take Care" and "Hold On, We're Going Home."

So now consider this week's fastest growing records at mainstream top 40:

1 - Pharrell Williams, "Happy" (up 12-10 on the mainstream chart);

2 - Lorde, "Team"

3 - John Legend, "All Of Me" (30-26)

4 - Jason Derulo, "Talk Dirty" (10-8)

5 - Beyoncé featuring Jay Z, "Drunk In Love" (28-22)

9 - Kid Ink, "Show Me"

10 - Aloe Blacc, "The Man"

Derulo's base is at mainstream and rhythmic top 40, but "Talk Dirty" is now indeed getting R&B airplay as well. So three of the top five, along with five of the top 10 are indisputably R&B records, and two more are shared between top 40 and the mainstream R&B/hip-hop format.

So how did it happen? 

Thank the rest of the world: "All Of Me" started at R&B radio, but went to No. 1 as a pop hit in Australia, Belgium and the Netherlands. "Happy" had been No. 1 in fifteen other countries, including France, Australia and the U.K. Blacc's "I Need A Dollar," unknown beyond its TV sync activity at home, was top 5 in Germany and No. 2 in the U.K., even before his mass-exposure here on Avicii's "Wake Me Up" finally made him a hit at home. For that matter, "Talk Dirty" had been a worldwide hit while Derulo's "Marry Me" was being worked here.

Retro-flavored R&B like "I Need A Dollar" or "Happy" is a growing part of the pop toolbox here, but it has been huge in Europe for the better part of the last decade. As important, AC radio is often both still dominant and more current-based in other parts of the world. Top 40 PDs have long been frustratingly likely to pick up an R&B record from a top 40 station in another market than from an R&B station in their own. It's aggravating to think that a crossover R&B hit has to travel around the world now, but so did Passenger's "Let Her Go" for the same reasons.

Thank Columbia: They've got Beyoncé, Williams, and Legend. And if they didn't decide to pursue the latter two at mainstream top 40, they probably wouldn't have happened. (Top 40 had, after all, the six months during which "Happy" was racking up No. 1s in other territories to come aboard on its own volition.) For the last few years, labels haven't seemed inclined to fight for R&B crossovers, especially if those acts can send different songs to top 40.  John Legend was probably not going to record a 125 b.p.m. paean to partying like it's the last night of your life. (Then again, nobody expected that from Ludacris either.)

Thank Boston & Seattle: '90s/'00s-based "hits and throwbacks" outlets like KHTP (Hot 103.7) Seattle and WBQT (Hot 96.9) Boston don't just play Notorious B.I.G. and 2pac. They play Jagged Edge, Ashanti, SWV and Brandy. Their success is a reminder that while hip-hop somehow became thought of as somehow more appropriate for top 40 in the '90s and '00s, R&B was always mass-appeal music. Ashanti's "Foolish" would have a hard time getting past adult R&B radio now, but hearing it on Hot 103.7 reminds you of what's missing from the format without R&B ballads. (Sobczuk also notes a lot more demand for '90s throwbacks when he spins in local clubs.)

Thank Beyoncé: When she reasserted herself in pop culture, mainstream top 40 wanted to be there. And for that  . . . 

Thank R&B Radio: Because in the five years since "Sweet Dreams," Beyoncé had remained a consistent hitmaker at R&B and hip-hop radio. (The most-played song on New York's WQHT [Hot 97] through much of the fall had been "Standing On The Sun," which wasn't even included on the subsequent album.) R&B radio may not seem to send a lot of product over to pop radio, but they absolutely deserve credit for the potency of Beyoncé's December surprise. And, for the second time with a Beyoncé album, it's the R&B radio track, not the initial pop track, "XO," that is turning out to be the hit.

Sobczuk may be too generous in one way. The echoes of the 1980-81 disco backlash are hardly silenced now. Even then, there were still a few R&B hits. There were MOR ballads like Quincy Jones & James Ingram's "Just Once." There were the girl-group throwback hits of the Pointer Sisters. There were "Upside Down" and "I'm Coming Out" by Diana Ross, whose own reigning diva status had just been reclaimed by her association with Chic's Nile Rodgers and Bernard Edwards. 

All of those songs have echoes now, although I feel confident that the "Happy" version of retro will endure better through time than the Pointers' "Should I Do It." If it's more recent comparisons you want, try the late '90s (a time when R&B crossover was rapidly expanding). We now have a successor to Brian McKnight's "Back At One" on the charts, but no "Too Close" by Next. 

In other words, R&B needed this handful of force-of-nature, undeniably mass-appeal songs to even achieve parity with the leanest years of the disco backlash. Unlike those years, when R&B's product was superior to top 40 and pop PDs ignored "Rapper's Delight," Rick James and the Gap Band, it's sometimes hard to say what other R&B songs ought to be making the transition.  It is nice to know that at this point the door might be open again for whatever else emerges.