Some resources for long-range weather forecasts include the Farmer's Almanac, the Weather Underground and the National Weather Service. These services also include past weather data as well as discussions of past and ongoing climate change.
The Farmer's Almanac has a long history as a print publication that forecasts weather events for the upcoming year. The print publication still exists, and some of the material in the almanac is reprinted on its website. Long range weather forecasts are available for every region and many large cities in the US and Canada. The Almanac makes 2 months of forecasts available free of charge through the website, but the full forecast is only available to subscribers.
The National Weather Service collects weather data from a network of satellites and weather monitoring stations maintained by federal and local government agencies. It uses this data to provide local and regional forecasts for both short-term and long-term time periods. Past weather data is available for review as well.
The Weather Underground bills itself as the first Internet weather service. While most weather forecasting services use National Weather Service data, the Weather Underground uses data collected by a network of over 100,000 volunteers operating personal weather monitoring stations. That data is collected and examined by a team of meteorologists and climatologists using a proprietary forecast model. Uniquely, the Weather Underground also publishes the accuracy results for forecasts.