I'm currently working out the same problem for my son. I've done the basic math for a simple slope with ramp ignoring any resistances.
Basically I used a quadratic equation to solve T, the time between leaving the jump and impacting (!) the slope, staring from three relationships - between height 'fallen' and time, between distance jumped and time and between height 'fallen' and distance. I still need to calculate the length of run up and adapt the computation to allow for an upward take-off... (including any deceleration from the ramp).
Later I'll be looking to add some models of different jump layouts and to start taking in wind and snow resistance.
= M =