Throwing upwind: I/O and keep it low
Throwing downwind: O/I and keep it high
Throwing downwind: O/I and keep it high
It even rhymes!!! Ok so what does that really mean...
0. Know which direction the wind is blowing
I know this sounds trivial, but to know how to throw in wind, you need to know which direction the wind is blowing. I don't know how much grass I've killed in the years I've played ultimate, but it's probably a fields' worth (grass grows back, right?! =P) I grab a few blades of grass and let it go at chest-height (where I want the disc to end up when I throw it to someone) and see where the grass goes... and that's the direction the wind is blowing.
1. Throwing upwind: I/O and keep it low
When throwing upwind, you're throwing into the wind, i.e. there is resistance on the disc preventing it from reaching its intended destination (both in the sense of time and space). In any instance of throwing upwind, the wind will catch the underside of the disc and push the disc upwards. This is what people mean when they say that the disc is "caught by the wind." This usually results in the disc shooting up in the air, and possibly flying behind you (my personal worst nightmare).
The solution is to throw the disc with an inside-out (I/O) tilt, and keep it low. The I/O angle gives the disc less effective surface area for wind to catch under it. In other words, the angle of the disc doesn't allow wind to push up from underneath the disc. Also, you want to keep the disc low to the ground because there is less wind closer to the ground. There will still be some wind to pop the disc up, so if you start at a lower position, the disc has more room to travel upwards, hopefully ending up at a level that's easy for your thrower to catch.
When throwing upwind, you want to put a lot of spin (extra spin!) and throw it a little harder than you would normally throw in windless conditions, depending on how windy it is. The extra spin prevents the disc from getting knocked around in the wind (it's more stable with more spin, give it an extra hard wrist flick) and the extra umph (from your torso and shoulders, NOT your arm) helps the disc overcome the wind resistance.
2. Throwing downwind: O/I and keep it high
When throwing downwind, the opposite is happening (duh Karen). The wind is giving the disc the extra push towards your intended destination (again both in the sense of time and space). So not only is the disc going to get to your receiver faster, it will get there with more force (the force of the wind plus the force of your throw). When many of us throw downwind (think of the go-to drill we did on Saturday morning), the wind pushes the disc down and by the time it reaches the receiver, the disc is lasering towards her shins/ankles/feet and she either dives for it or does a little hop over the disc so it doesn't take her feet off!
The solution is to throw the disc with an outside-in (O/I) tilt, and to keep it a little higher than normal. The O/I angle allows the disc to be "carried" by the wind to its destination. (Conversely, if the disc has an I/O angle, the wind will push the disc down quickly from behind, usually resulting in a turfed disc, that is, the disc hitting the ground sooner than you'd expect it to.) I also like to throw a little higher when I'm throwing downwind, like releasing the disc at waist- to shoulder-level. Again, this gives a little bit more room for error as the disc is getting pushed down by the wind.
When throwing downwind, you don't have to throw as hard, as the wind is "helping" the disc towards its destination. Sometimes people will tell you to "take a little bit off", i.e. don't throw as hard! Even if it looks like a great throw, hard downwind throws are really difficult to catch for in-cut receivers because they're flying towards the receiver so fast. As with the upwind throws, downwind throws also need a lot of spin. Spin keeps the disc stable and prevents it from getting pushed around by the wind.
3. What about in a cross-wind?
Well, crosswinds are just linear combinations of upwinds and downwinds, if you will :) Suppose there is a crosswind from left to right. Common sense tells us that all our throws, no matter I/O or O/I or what, are going to have a tendency to tip towards the right side of the field. As a righty thrower, that means all your backhands are effectively going downwind and all your flicks are effectively going upwind. For backhands, throw with O/I and don't throw as hard. For flicks, throw with I/O and use more force.
- Throwing upwind: I/O and keep it low, throw a little harder, lots of spin!
- Throwing downwind: O/I and keep it high(ish), throw a little softer, still lots of spin!
- Crosswinds are linear combinations of upwind and downwind
One easy throwing drill is to just stand 20 yards from your buddy and throw 5 forehands and 5 backhands. Then both of you take one or two steps to your right (imagine you're walking to form a large circle with a diameter of 20 yards), and throw another 5 forehands and 5 backhands. Keep taking steps around your imaginary circle and throwing both forehands and backhands, adjusting to the wind as it changes direction around you.