Rain calibration corrections

This morning my Sky is not registering the drizzle that is falling. About .01" of rain fell according to conventional rain gauge but nothing on Sky. So it appears the Sky isn’t sensitive enough on low intensity rainfall but too sensitive with higher intensity rainfall giving totals 3 to 4 times higher than actual.

EDIT. As a follow-up, today’s rain event was a warm rain process-tropical type process with lots of small droplets. Sky reported 0.192" vs 0.34" rain gauge. This is the first time for me that Sky actually under reported a significant rain event since it is usually 3 to 4 times over for larger rain drop events.


It must have heard us talking about it! recorded rainfall yesterday and today.
The rain is more than misting though - the kind that gets you soaked quickly without being felt as falling drops.



Just to follow up now it stopped raining. I have no way to measure the rain, but Alexa told me this morning to expect about 8mm of rain (not sure what service they use). Dark Sky said 11.3mm of rain. Sky reported 9.07mm, so for me, so far, seems relatively accurate.

We have only had a couple of rain events so far, and I never even thought to check elsewhere for a comparison, so today was the first time I did that.

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Question for the WF staff - it’s still in the super-dry/wildfire season here between Seattle and Tacoma but it’s going to start raining again in about a month (typically) and be the usual ugly for many months thereafter with morning marine layer heavy-mist and general grey consistent light precipitation a ridiculous percentage of the time.

I have a VP2 and a CoCoRaHS gauge that typically match exactly. The VP2 is online at all the usual places (PWS, CWOP, WU).

For your continuous learning tuning, how do you know what actual reality is ?

  • in this area you can’t go by the SeaTac airport readings, as there is too much variation depending on your actual location and elevation

  • there are also of course lots of cheapo stations online nearby that have bogus data online so you can’t try to cook up some aggregate lat/lon-based average or the like.

  • any particular station of course could have errors as well such as blocked weep holes, weak Reed Switches, not-level mounting of the tipper gauge etc. (just to mention three typical Davis issues I’ve seen in almost 10 years using one).

  • the Internet site (WU most noticeably - ugh) can even drop a lot of posts so the online data is likely imcomplete

So how do you tune the units to reflect actual reality ? Just curious…

I can tell you think about this stuff a lot, @vinceskahan! And you ask all the right questions! Are you looking for a job?

Seriously, we use a wide variety of “trusted sources” for the validation portion of our continuous learning system, and we’re always exploring more. They vary by parameter and location and range from networks of gauges to pure numerical models and everywhere in between.

For rain, nothing beats a co-located, high quality 8" tipping bucket that’s been recently calibrated, but that’s hard to find - as you point out. The next best source we’ve found (so far) comes from a small company that specializes in accurate, high-resolution modeling (based on gauge data as well as radar and satellite).


Hi, not sure how this forum works, can’t seem to find a reply button to add to others remarks.
I installed my unit yesterday. It was a very windy day with a little rain. I installed it next to an official rain gauge. I took 1.6mm from the gauge this morning and the weather Flow measured 3.45mm. I will shorten the mounting pole to decrease vibration to see if this helps. I also believe the QNH reading to be a little high. I lowered my site elevation by 7m in the setup menu to compensate. In future would it be possible to have an adjustment in the app to allow for calibration? Something that shows a plus or minus from the factory setting.

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Hi. Welcome to the forum! We moved your post to this thread which is mostly a discussion of rain calibration issues. See the long thread above!

Note the pressure sensor is in the AIR device (not the SKY). Be sure to set your “elevation” to the ground’s height above sea level and the “height above ground” for each device (AIR & SKY) to just that: the vertical distance from the surface to the device.

We do intend to add a user calibration feature to the app eventually, but normally your pressure sensor should auto-calibrate (assuming your elevation and height above ground values are set properly). If you suspect it’s out of calibration after a week or so, drop us a note at support@weatherflow.com or http://got.wf/contact


Thanks David, I have readjusted the Air units hight. I’m wondering how the units self calibrate, I could understand if there was a calibration standard in near proximity. Particularly with rainfall. Yesterday we had 11.2mm, the Sky measured 17.2. I’m not complaining but just wondering if there’s any way of helping?



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Hi Langdon. It’s okay to complain! Your rain sensor’s accuracy will improve, but it may take a little time while we sort through all the data, run it through our algorithms, and repeat, repeat, repeat. See my reply to Vince, above, regarding what data we use to calibrate your rain sensor. Short answer: many.


Reported in another forum but this one is closer to the mark.

SKY has been measuring here for several months. I know you’re still working tons of hours on fixing things, but Sky is still reporting inaccurate rain data despite months of reporting problems by many. Not good.

In past 24 hrs, rain is way off:
… WeatherFlow Sky: 12.1 mm rain
… Davis Vantage Pro 2 on same pole as Sky : 6.6 mm
… NetAtmo: 7.6 mm

Getting a bit discouraged. I would suggest you describe the firmware as BETA until things are fixed. Some measures are working better now (temp and humidity) but the standard deviation and error rates of other data are much too high across the world to be reliable.

In my view, the unit is not ready for prime time. I’m happy to continue being a beta tester as needed, however.

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Just installed mine yesterday, Last night it rained. My Sky recorded 8.74" while most other stations showed 1.3"
Just an FYI since I read this entire thread and I know you’re working on it. 4834 is the id.
Mounting is a 14’ Steel 1.325 gas pipe attached to a steel shed.
BTW I love this thing,
Weather Geek Chuck


that makes me feel good – I was one of a few non-beta testers to get my SKY first – ive had trouble with rain measurement – ive had bout 2 rain events - however very slight rain events – going 6 months or longer and only getting 0.30 of rain — may take months or years to calibrate the rain measurements

My first rain event and I netted out 1.81(over a 30 minute TStorm) Higher by one inch over the surrounding PWS.

No false readings since installed 1week ago



Hi Chad. I moved your comment from the photos thread to this one. See above for lots of thoughts! We’re actively addressing this issue and appreciate your observations and patience while that goes on. Expect some odd rain totals in the short term that will get better over time.


Thanks much! I realized I double posted

Here’s my station. Two rain events 1.51 and 1.81. (Local reports .3 and .4) Haven’t done the sand and bicycle tire just yet. Sky was moved about 100 feet to the left of this picture to avoid any interference.



So… I know there are plenty of topics on this, so my point isn’t to beat a dead horse on this topic. I just thought I would show my graph data from my first rain event this evening. It basically rained according to the sky at a rate of just over 1" per hour but only rained for 12 minutes. The total was 1.07" which clearly is too high. I don’t have another gauge that I was able to compare it to other than radar estimates. Anyway, I just wanted to see if the calibration was going to come in a firmware update, or if there was something specifically needed for my station? Also, you may be capturing this data automatically from all stations and analyzing it, but if not, here is some more data for you to look at. I love this product and look forward to seeing some of the minor kinks worked out of it soon.


Rain calibration is not yet out to the large public. Just a few testers have it (no not me :wink: )

WF will tell when they roll it out to all.


3 posts were merged into an existing topic: Small Birds Causing Rain

The calibration updates will come in the form of firmware updates and backend updates to the rain component of the continuous learning system. Nothing you need to do specifically, but you’re welcome to continue posting your observations here!