If you would like to use a PWS on wunderground and discover that it occasionally goes down without notice you can try this trick:
Open the wunderground site and do a search for the pws.
Look for the latitude and longitude coordinates. (38.936 -104.726 or ##.## N ##.## W) All South(S) and West(W) locations need a -(negative) in front of the numbers
Copy that number down and log into your opensprinkler. In the bottom right corner select edit options.
Where it says location put the numbers you copied in separated by a comma with no spaces: 38.936,-104.726
DO NOT hit the little location map pin on the right side of that input box.
Then hit Submit in the upper right corner.
Now make sure the weather shows up on your main controller status screen. If you have done this correctly WU will now get the weather for that original station or the next closest one if it’s down. I was told a while back that this may cause an issue with something somewhere, but after a full year of running I have had absolutely no problems, so take my advice with the knowledge there is a slight risk in something going wrong.
ET is bascally how much water a plant loses in a given time period, kinda like measuring how much a person sweats in a day. The calculation can be used to figure out exactly how much water a plant would therefore need to replenish the water lost. Since most plants that are watered have an above ground component, solar radiation plays a factor in the ET calculation. So even if you use a subterranean irrigation system you would need the solar radiation calculation to get an accurate ET amount. Solar radiation can be estimated using your location and cloud cover information from WU, so while not essential actual solar radiation will improve your calculations and help reduce over or under watering.
If you would like to research ET and it’s application to irrigation look up: Penman-Monteith ETo or Hargreaves ETo, as these are the 2 most widely accepted methods.