Houthi victory in Yemen looked almost certain for months. Through the spring, the Houthis had pushed government troops into Aden and had almost taken the city. Had Aden fallen, government troops would have likely been unable to recover, their main forces having been destroyed.
Yemen, 4/1 - Note Aden in dispute. Red is government control, green is Houthi rebel control, grey/black is ISIS/al-Qaeda control, and yellow is Southern Resistance movement control (they joined the government this summer)
Through late spring and summer, the Saudis have been arming government troops and bombing Houthi positions. For some time, the situation seemed to be delaying the inevitable. But, almost-miraculously, government troops in Aden held on and then launched a counter-attack that drove the Houthis out of Aden and secured the port city in late July. The Houthis attempted a counter-attack, but were repelled.
In the two weeks since, government troops broke out of Aden to take the surrounding environs.
And in the previous three days, the government army accelerated its advance, linking up its split eastern and western forces, and also advancing towards the north of Sana'a. It's a fairly incredible turnaround.
The majority of Houthi forces are likely being pressed in the south, which means the threat to Sana'a in the north may be quite realistic--particularly with Saudi air support.
We'll keep an eye on it.