It seems like people are obsessed with rainfall and ET values. Rainfall is not part of the ET equation. Rainfall can affect ET, but ET values change very little over a 20 mile range. The most important part of rainfall is effective rainfall. Effective rainfall is impacted by rainfall intensity, soil type, root depth and texture. If you get 2 inches of rain in one hour timeframe on heavy clay soil, there is only 1/10 inch per hour intake rate. So i continue to believe it is more important to have quality weather station data versus worrying about rainfall totals. Oklahoma where I live has so many weather stations because of our severe weather. Yes, we have localized downpours here, but most runs off the landscape becsuse of runoff on our clay soils.
Good link: https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.fao.org/docrep/r4082e/r4082e05.htm&ved=0ahUKEwj0w_jImuTUAhUK3IMKHaMfBnIQFggnMAI&usg=AFQjCNGa_L7pms9RHj0KJk5TTpUcKI8EUw


I find it funny you say 20 miles, 1 mile here in Colorado can make a difference between 1" and 0" rain. I have my own local weather station, and it makes all the difference.

You really have runoff issues?