Most weather forecasts are pretty good at up to a week out, and even general trends to 10 days or more can be helpful for planning purposes. Climate forecasts for general patterns several months out can also be good, especially when there is a strong El Niño or La Niña event occurring. But in the two week to several month time scale, it is hard to make a good forecast. This article describes why that time scale is so tough to get right and describes some new methods for extending useful forecasts into this tricky time period. You can read it from NOAA here.
