It's hard to tell exactly what all happened, but it looks like his front left tire touched the slushy median. He felt this change through the steering wheel and he tried to straighten the car which ultimately put both driver side tires on the slush. He may have had a minor panic attack from the feeling of having two tires on asphalt and two tires on slush and tried to steer his car back into his lane too sharply. This sharp adjustment caused the vehicle to start in a slide to the right. And most likely from here, with the vehicle sliding to the right he panicked and steered too much to the left, so when he 'stopped sliding' by hitting the van his wheels were still pointed to the left which caused his vehicle to drive to the left (makes sense right?) and into the way of the 18 wheeler.

Something a lot of people don't think about is, in most cases, the car is going to go where the wheels are pointed. For example, watch this video of a subaru sliding at high speeds and keep an eye on the driver side wheel, notice how as the vehicle slides the driver keeps the wheel pointed straight because that's the direction he wants the car to go in, also notice how quickly he turns the steering wheel.

Now about fixing it, obviously it's a lot easier to arm chair drive from the safety of my desk where I'm calm and have plenty of time to analyze a situation. But I would suspect initially, had he made very minor steering adjustments to try and bring the vehicle off the slush he would have been fine. Also when he hit the van had the wheels been point straight or slightly to the right (instead of left), he may not have driven into opposing traffic.