It depends - surely, studying the weather (how much snow there is on the mountains in winter affects how much water there is in the rivers in the spring) can reduce, if not remove, the risk of crop failure. Perhaps you have the choice of a more expensive drought-resistant crop and a cheaper one that isn't.
Breaking the feedback loop by subsidizing failed crops doesn't create any incentive to invest effort into making good decisions in these areas.
You're making the assumption that winter snowpack has a dramatic effect on farming success. Sure, it helps fill the aquifers when it melts, but farmers depend on rainfall (at least in the US) as much as they do on irrigation. Heat also makes it hard for crops to grow successfully, regardless of how much water they get through irrigation.
The returns a farmer receives depends also on the price the crop can receive. Barring futures contracts, for widely-traded crops such as wheat, soya and corn, this will depend on the global market, i.e. not only the local weather, but also the weather in Brazil, Australia, etc.
Breaking the feedback loop by subsidizing failed crops doesn't create any incentive to invest effort into making good decisions in these areas.