Not really an answer, but an extended comment:
Power is dispatched on a very short time scale. If I know that I'm likely to have lots of wind power at 3 p.m. today, I'll start to lower the feed rate to the coal fired boilers at 2 p.m. picking up the slack with gas turbines, shutting down the gas as the wind picks up.
Forecasts a few hours ahead are quite accurate. (I routinely get rain forecasts that are accurate to within 15 minutes 6 hours ahead) I don't think short term forecasts are much of a problem.
Long term, you are working with climate data. Your non-renewables need to be able to cope with full renewable shutdown anyway, so any renewables you get just decrease your operating expenses.
PV is more predictable. You know the envelope -- no power at night. And even cloudy days produce reasonable amounts of power. (Germany with it's gloomy skies still generates about 800 kWh/year/installed kW while Arizona doesn't quite make double that.