Rain reports to WU wrong

Something seems to have changed with rain reporting? My Dalyan station has had a small shower of rain. My SmartWeather dashboard shows it correctly but WU shows the rain rate continuing since the start of the shower, but without an increase in the total rainfall.

Rain was between 09.52 and 10.02hrs local.


Also, a similar issue with my Southsea station. A single event at 06.52hrs but shows on WU as constant rain from 06.54 till 07.59hrs. The only reporting difference is that this station relays via a Meteobridge hub.


Has something changed? Any ideas @dsj

I’ve just noticed that this behaviour has been going on for a while, certainly since the 20th September. Seems very odd.

Hi @val . Nothing has changed on our end (although it’s possible Weather Underground changed something on theirs). We report data to Weather Underground every minute with the total accumulation for the day, along with the previous hour’s accumulation. So it’s a rolling one-hour rate value; the total amount of rain collected over the previous hour.

There are other ways to report hourly rate, but that’s what it seems like Weather Underground is displaying for other weather stations. We can’t find any definitive documentation on the value WU expects for “hourly rate”. If you know of any, please let us know!

Surely ‘Hourly Rate’ is the rate per hour, at that moment, not the amount of rain in the past hour?

If you are reporting the ‘total rain in the last hour’ and not the ‘rain rate’, but they expect the ‘rain rate’, that would perfectly explain what is wrong with my WU graphs!

I don’t understand why nobody else has picked up on this though.

If you compare my other Dalyan station

with my WF station

the issue at 13.30hrs is perfectly obvious.

@dsj This discussion is relevant


I would seem that if you want WU to display accurate rain rate information you need to send the ‘rainin’ value as ‘rain rate’ not ‘rain last hour’

If you look on the ‘table’ version of their graphs, I’ll bet the ‘Precipitation Rate’ column is taken verbatim from the ‘ranin’ figure reported.

Thanks for the link! That discussion feels familiar (I think I read it, or something like it, last year) and points out a couple things:

  1. The definition of “rain rate” completely depends on the time reference. The smart weather stations report the amount of rain collected over one minute. This raw value, which is “rain per minute” is not meaningful to most folks, but it’s a valid rate. To make it more meaningful, it can be converted to an “equivalent hourly rate” by multiplying by 60 (how much rain would fall if it rained the same for every minute of an hour). Or it can be summed with the previous 59 one-minute values to provide an “actual hourly rate” (literally how much rain fell over the past hour).

  2. The Weather Underground PWS documentation (before they took it down) defined two values, “rainin” (rain inches over the past hour) and “dailyrainin” (rain inches so far today in local time). That’s what we give them. There is speculation in that thread about how WU converts or displays those values in the graphs, and it’s possible they made a recent change, but from the data we have reviewed today, it looks like they are displaying exactly the values we’re giving them.


I know this is old but this still seems to be an issue. Rain amount in WU is pretty much always wrong. It worked perfectly when I had an Ambient Weather stations. Surely tempest devs can do some trial and error testing and fix this . . .

example: KWACENTR95, 4/27 5:37pm, current accumulation in WU: 0.25, in Tempest: 0.17

The daily accumulation actually goes down sometimes. This should NEVER happen except for at midnight. My guess is Tempest is sending a 24 hour period of rain from a sliding window of 24 hours, instead of “since midnight”. (also possibly without using the local timezone, as well)

Try this Google App Script forwarder developed by Leo, it takes data from Tempest API and forwards it to Weather Underground at one minute interval instead of the five minute forwarding interval from WaetherFlow. It runs on Google server, so does not require any additional hardware, just requires a google/gmail account.

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it is not using a sliding window, it is reporting accumulation since midnight. However there is an option in settings to show the NC (near cast) data, which basically corrects the amount measured after the fact. That might be what you are seeing.


I think near cast only applies to what tempest shows and not the WU feed but I’m not sure. I do have that off. Regardless like I said, an accumulation should never go down except at midnight when it resets and it goes up and down all day (see graph I posted). You can’t subtract rain you already received. Makes no sense. ands when looking at WU the only stations that go up and down during the day for accumulation are Tempest ones.

Looking at Tempests own data for my station (still with nc off) everything is correct and the rain acumulating only goes up each day, as it should. It’s only a problem with the WU data feed.

@karss awesome. I’ll try that. Thanks.

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with NC off, that can’t be an issue. And when it is correct on the tempest it definitely can’t be an issue. I don’t use WU so besides the NC (which clearly isn’t the problem) I have no other suggestions.