RainMachine has the ability to interface every 6 hours by default with NOAA and has the ability to interface with many other Weather Stations and Weather Forecasting Stations.
Weather Station - Has observed (measured) observations from weather stations
Weather Forecast - Has weather predictions for future days
With the introduction of multiple Weather Data Sources, you now have greater flexibility in Smart Forecasting. Not only can you select more than 1 data source but you can see a side by side comparison of them as well.
Notice you see a red line which is the "RainMachine Mixer", this is a combined average of the enabled "Weather Services". Note some of these are only available in certain areas, take for instance "FAWN" this service is available in Florida.
Here is a list of the currently available Weather Services:
DarkSky - Global weather service from https://forecast.io
FAWN - Florida Automated Weather Network Observations
CIMIS - California Irrigation Management Information System weather stations
WUnderground - Global weather service with personal weather station access from Weather Underground
Netatmo - Weather observations from NetAtmo personal weather station
METNO - Global weather service from Norwegian Meteorological Institute
NOAA - North America weather forecast from National Oceanic and Atmospheric Administration
Enabling multiple data sources will allow you to see a comparison to pin point the one that is the most reliable for you. We don't recommend leaving more then 2-3 enabled for long periods of time.