Introducing RainCheck

At long last, we’re rolling out some significant updates to the way we report rain data from your SKY devices – starting with users in the Continental USA. The haptic rain sensor in the SKY 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 and compares it to a quality reference source. We’ve looked at many reference sources including CoCoRaHS reports, co-located tipping buckets, radar estimates, NASA analyses, and more. We’ve found one of those reference sources to be exceptionally good. It’s a real-time precipitation model called MetStorm®Live (MSL), from a small company called MetStat. For many weeks now, we’ve been using MSL, and data from your SKY, to produce what we think is 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 against the reference MSL 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’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 does a great job without RainCheck, you can opt out of it by going to the “advanced” settings view for your SKY 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 device. Calibrations will continue to improve as more and more rain events from your SKY 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 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 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 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’s precipitation data is pushed to WU or not via an option in the app.


  1. The RainCheck system is able to use other sources of precipitation data, but currently it only uses MetStormLive.
  2. The MSL data (and therefore this initial version of RainCheck) is currently only available in the continental United States which explains why we are starting with users in the US. We are actively evaluating other valid quality sources of precipitation data across the globe, including the possible expansion of MSL.

Always improving. :rocket: Cheers. - the WF team


Excited to see this. It sounds like a great solution. Of course I’m bummed to be located outside the contiguous lower-48 states though. Here in Alaska, we’re a little data sparse but I would hope there is enough available data to expand RainCheck calibrations to this part of North America. Would really love to see the MSL data expanded to include Alaska.


Awesome! Will this hopefully fix the issue where heavy rain is underreported? I know in thunderstorms here in the US I’ve had the final amounts be 2-4x lower than nearby stations and radar estimates indicate, mainly during thunderstorms or heavy rain events.


I assume this will mean that over time the Sky’s reported rain should eventually match the RainCheck value.


I live in a region with very isolated rain/thunderstorms. I often get accumulation when the Dept. of transportation station 2 miles away shows 0. I want CL, but still desire autonomy from the ‘official’ readings. The corrected rainfall from Saturday now shows 0.00", whereas we had several downpours in the afternoon that originally reported .08". Also of interest, the daily accumulation over the last few days is now 0.00, but I still have duration reports of 6 minutes, 5 minutes, etc. :slight_smile:

I studied your approach to “always improving” using this forum before I purchased my system a few weeks ago. This kind of serious improvement work is another great example of the WF approach to this set of devices - congratulations on continually working with your users to improve the experience and giving users the ability to opt-out if they don’t like the change. This will lead to much success for your company. I looked at my station via a web browser a few minutes ago and saw that logo already showing next to yesterday’s data.


This is the last 7 days readings from my peet bros pro
compared to my Sky. Sky is column two. Not bad !
.04 .04
.03 .05
.00 .00
.21 .17
.84 .83
.40 .37
.65 .87


Do we have an exact date to look for on this update. Last storm my weather flow was off by over 2”. Was a very heavy storm. Actual total rain fall was 3.49” WF showed 2.05”. This data was for June 6, 2019 in Farmington AR 72730

It should be visible now or at least by tomorrow. Check your station on the Web if you don’t have the updated app yet. If you see the RainCheck logo next to yesterday’s precipitation value, then it is in place.


Merci pour l’info, à quand l’utilisation de ce service en France ? :slight_smile:

Mine actually adjusted the rainfall amounts for everything I’ve seen in June. It fixed a lot of the low amounts and bumped them up much closer to where they should have been. Try going back in the weatherflow app and checking the history for that day to see if it changed.

I saw that past rainfall totals have changed upward for me.
My question is if the current rainfall amounts are affected. We are having heavy showers now and WF has .37" but my Stratus rain gauge has .55". Rain check is on.

We agree!

Yes, RainCheck will help with both under- and over-reporting in the raw values.

Correct, over time the difference between the raw value and the RainCheck value should decrease.

Very interesting. It’s definitely possible for RainCheck to miss very brief showers that your SKY records, resulting in RainCheck “zeroing out” rain that actually fell. We will be looking at improved rules for when RainCheck should “zero out” raw data (essentially tagging it “false rain” - which is another part of the CL process for rain), vs. leaving it non-zero.

Note, when RainCheck “zeroes out” your SKY this does not affect the ongoing auto-calibration part of the CL process for your SKY.

Good catch. There was a bug in the web app causing that issue, and it has just been fixed. Please let us know if you’re seeing this bug in one of the mobile apps.

Thanks for being one of those engaged users, Ron!

RainCheck has been running since June 1. Checking your station, the RainCheck value shows 2.74" for June 6 at your location.

Not directly. RainCheck is updated once a day for yesterday’s rain so it does not apply to current (raw) rainfall amounts shown in the app. Look for the RainCheck logo to indicate the RainCheck value.

I say “not directly” because the ongoing auto-calibration side of the rain component of CL will adjust the calibration over time, and that does affect the raw value you see before RainCheck runs.


2 posts were split to a new topic: Rain Check in API?

I am not clear on where the setting is to allow the rain data to flow into weather underground.

Referencing this post:

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’s precipitation data is pushed to WU or not via an option in the app.

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It’ll update the next day after 8am with the adjusted total. As time goes on the calibration will bring it so that both are pretty close to reality. How close did yours end up being to the stratus after adjusting?

This last rain was strange. WF had .38" before calibration. Calibration brought the total WF rain to .39".
Stratus had .55".
The previous adjustments brought the WF very close to the Stratus gauge.

I would say in a few weeks it should get pretty close to it as the CL process continues. I’m still waiting for a good thunderstorm here but already I had a nice heavy shower. It showed .18 and radar estimated .18-.20 over my house so pretty much dead on. I’m pretty excited because previously a heavy shower like this would register .08-.10 and would be too low.

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Sorry if I missed this detail, but can I still view the previous raw, uncorrected rain data somewhere after 8a each day? I myself am a CoCoRaHS observer and have been keeping tabs on my manual readings vs. observations from SKY. (Needless to say, they’re really close!)

I have an example from last week even where the two were off by 0.06” (WF: 0.16, me: 0.10, not bad really) but now WF changed to show as 0.11 with RainCheck. If I hadn’t jotted the old reading down before this change (or gotten to it before the correction was applied), I’ll no longer be able to monitor this.

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