At long last, we’re rolling out some significant updates to the way we report rain data from your SKY/Tempest devices – starting with users in the Continental USA. The haptic rain sensor in the SKY/Tempest is an incredible little device. Unlike a traditional tipping bucket, it can measure 5 dimensions of rain: immediate onset, relative intensity, duration, rate and accumulation.
That said, it has proven quite difficult to define an out-of-the-box factory calibration for accumulation due to the wide variation in siting locations, mounting techniques & materials, shifting winds, and a plethora of other variables. On top of that, it is difficult for any single weather station (collecting data from what is effectively a single point) to provide totally accurate rain accumulation measurements for a broader area (like your yard, or your neighborhood). This is not specific to the haptic sensor - two perfectly-calibrated rain gauges of any type often report different values for the same rain event, even when they’re located immediately adjacent to each other.
To address both of these issues, we have been developing a process that analyzes the rain data from each SKY/Tempest and compares it to a quality reference sources including CoCoRaHS reports, co-located tipping buckets, radar estimates, NASA analyses, and more, with the goal of producing the best estimate of precipitation accumulation available.
Introducing “RainCheck”
We’re launching “RainCheck” starting with all owners in the Continental USA. Every day, between midnight and 8am (depending on weather conditions), RainCheck compares the raw accumulation calculations from your SKY/Tempest against the reference data set for your exact location to create the most accurate representation of the average rainfall available. The result is the “RainCheck” value - it’s your SKY/Tempest’s data, only better!
Beginning with iOS and Android app v3.10, you’ll see the RainCheck data annotated with the “RainCheck” icon next to the associated accumulation data value. If your SKY/Tempest does a great job without RainCheck, you can opt out of it by going to the “advanced” settings view for your SKY/Tempest device in the app.
The RainCheck analysis is also what will drive the “Rain CL” process for both auto-calibration and quality control. RainCheck analysis data from multiple rain events will be used by the Continuous Learning (CL) system to produce a unique set of calibration constants for each individual SKY/Tempest device. Calibrations will continue to improve as more and more rain events from your SKY/Tempest are analyzed.
On the quality control side, the RainCheck analysis also looks for “false rain” and “excessive rain” events - both of which can happen for many different reasons such as wind-driven vibrations. As part of the RainCheck analysis, algorithms are applied that determine whether a particular rain event looks like false or excessive rain. These QC flags will be used to identify individual SKY/Tempest units with chronic false/excessive rain, in order to proactively notify the user, providing tips to help take some action to mitigate the issue.
We have found that a well-calibrated SKY/Tempest device installed on a stable mounting position, free of vibration, will produce rain accumulation values that are remarkably good. The launch of RainCheck will improve the accumulation values reported in cases where a particular SKY/Tempest is not ideally mounted, which is difficult to do in many home locations.
As part of this rollout, we will also be making a change to the way we push data to Weather Underground. In the interest of quality, since RainCheck operates several hours after the data is collected, and since WU is unable to update data after the fact, we will NOT be providing precipitation data to WU by default for new stations linked to WU. There will be no change for existing users. And all users will be able to specify whether their SKY/Tempest’s precipitation data is pushed to WU or not via an option in the app.
Notes:
- The RainCheck system is able to various sources of precipitation data.
- RainCheck is currently only available in the continental United States which explains why we are starting with users in the US.
Always improving. 
Cheers. - the WF team