Weather Intelligence and Evapotranspiration


I can’t find detailed information on how Rachio calculates for evapotranspiration and what data they gather from a PWS versus commercial providers/systems. What data is used from Personal Weather Stations and what data is used from other sources?

In my case I have a ten year old controller system that uses its own temp sensor/rain sensor at my house to run algorithms to calculate the evapotranspiration and adjust the system run times. I currently have a PWS that measures temp/wind/rain amount/solar radiation and reports that to WU. Is there any efficiency gain to move to a Rachio 3 controller?


Found this link referenced in the forums multiple times but the article no longer exists and I can’t find a replacement.


We use penman monteith ( with the closest National station data or forecasted data.

We use precipitation observations from PWS.

Seems like you are hyper dialed in!

One feature you might not have (other than internet connected control) is watering skips due to forecasted weather.

Here are some features your old controller might not have


From your reply it sounds like you find (or the user sets) the closest National Weather Service recognized weather station to gather solar radiation, wind and temps and if the user has a PWS use that for rain collection data. Is that right?

That does not seem to line up with the marketing around Weather Intelligence Plus. Is there a white paper or some more detailed information you can share (or point me to) that describes how WIP works? The Support article is a pretty high level view without much detail.

I ask because where I live microclimates are a real thing and I decided with my first purchase of a smart controller that a temp/rain sensor at my house using statistical data for solar/wind would be a better result than connecting to a weather sensor a mile or more away from my home. Thanks.



How we derive ET is the same whether you are using WIP or not. It does have much better weather intelligence than Gen1/2. We give the user two distinct options now.

Interpolated weather data that you don’t have to worry about stations going down or not reporting precipitation which takes the burden off the homeowner of making sure they have an accurate reporting station. Interpolated data is great but won’t be exactly the measured amount that a PWS would give you near the house.

The ability to choose from over 250,000 PWS stations (Gen 1/2 has about 40,000 PWS stations). 80% of controllers are within 1 miles of a WU PWS station. For contrast, only 8% of Gen 1/2 controllers are within 1 mile of a (PWS,CWOP) or National station. I’m also wrapping up a WI plus feature that will self “heal” a chosen station, always making sure you are using one that is online, automatically choosing the next closest station.

If you can connect your PWS to WU and use our flexible daily schedules, I think you will be surprised at what the system can do. I’m not trying to oversell but no other controller will do what our flex daily schedules do. It’s extremely difficult and I guarantee none of the cheaper models (ahem…) have that level of sophistication. ET might be your only issue (not produced from your station), but how we derive it has worked great for most folks.



I had an experience a while back where, as I understand it, Rachio did use my PWS to calculate ET due to a NWS station temporarily disappearing around midnight. It was much much lower (up to 0.05) than it should have been based on ET calculated from CIMIS stations and not even close to forecasted values. I was happy to have that resolved as my plants were being underwatered due to the cumulative sum of low ET. Some PWS may be great for calculating ET but not mine.


The main factor is wind. Most people don’t have their station setup correctly. The recommendation is that standard wind measurement should be taken at 10 meters (33 feet) above the ground. I have yet to see a PWS do this correctly :joy: