Rain reported after it stops raining.

[pjwxman]

Hello all.

Does any one know how to configure Cumulus to stop reporting rain to Weather Underground when it stops raining?

The following happens when it rains. It'll rain for 5-10 minutes but Cumulus will continue to send non-zero rainfall amounts/rate for up to 1h. It will also usually taper it off before going to zero. For example, it rained for a few minutes today and Cumulus sent 0.04" at 18:00; 0.06" at 18:10 (it stopped raining between 18:10 and 18:20) but it sent 0.06" every 10 minutes until 19:00 when it sent 0.02" and back to 0.00" at 19:10.

VP2 data being logged by Cumulus reflects the actual rainfall event and reports zero once the percip stops.

Also, the Rainfall Rate (Hourly) is actually a 10-min total, not a rate while it's raining, until the above happens.

It did it with Cumulus 1.9.3 builds 1057, 58 and 59.

Cheers,
Pat

[steve]

The only rainfall figures that Cumulus sends to WU are the rain in the last hour, and the rain so far today. Those figures are the ones on the Cumulus main screen. I don't know what WU does with those figures. If you turn on the debug log, you'll be able to see the actual data that Cumulus is sending to WU; the "rainin=" figure is the rain over the previous hour in inches, and the "dailyrainin=" figure is the total so far today, in inches.

So, if the figures being sent to WU are wrong, I'd expect the ones being displayed by Cumulus to be wrong also.

[RayProudfoot]

WU do strange things with the rainfall data. I'm sure they average it rather than show actual rain rates.

My WU station is ISTOCKPO4. Have a look at my rainfall rate for 12 August 2010 between 16:30 and 17:30. In that hour I recorded just over 1" of rain - my all-time record. My WU rate only shows a peak rain rate of 1" but Cumulus recorded 3.75" per hour.

Aug12.jpg

And yes, they do show rainfall long after it's stopped raining. One reason I don't rely on their rain rate or duration data - just the totals.

[pjwxman]

Thanks Ray,

My issue isn't with the amount reported. Other than the mm to inch to mm conversion, the amount is correct. I'm just wondering why when it stops raining, the rainfall rate doesn't drop to zero. Look at some of the rainfall graphs on WU from various stations and you'll see a bunch of them have upward slopes, flat lines and downward slopes, indicating a constant rainfall rate for long periods of time.

Cheers,
Pat

[RayProudfoot]

Hi Pat,

Yes,I agree that the totals are correct but their graphs aren't. I'm looking at one of my rain days on WU and it started to rain at 17:36 and the last increment in the day total was at 17:41. The total increased by just 0.02" but WU continued to show a rain rate until 18:37 - nearly an hour after it stopped!

It's worth you raising a ticket to query their way of calculating the rain rate as it's been weird for years. They are also running a Feedback option that alows you to submit suggestions for improving their service and to vote on those already submitted.

[steve]

I'm just wondering why when it stops raining, the rainfall rate doesn't drop to zero.

Presumably because what they are calling rainfall rate is actually the 'rain in last hour', so it takes an hour after it stops raining for that figure to drop to zero. You can see that on Ray's tabular data for that day. It stopped raining at 1806, and the rate/last hour figure dropped to zero at 1906.

[pjwxman]

First I want to thank both of you for the replies.

I have the debug.log running which will hopefully shed a bit more light on the subject next time it rains. The Cumulus display and Davis console have always shown the same values.

For a previous rain event, I compared the data in a file called "Feb13log.txt" to what was sent to http://www.wunderground.com//weathersta ... NEWSOUT155.

From the Feb13log.txt file, it rained between 09:28 – 09:49 Local (22:28 – 22:49 UTC). The value was zero at 09:50L. The data sent to WU was:

INEWSOUT155 2013-02-14 22:20:00 71.1 66.7 30.160 0 0.0 3.0 86 0.00 Cumulus v1.9.3
INEWSOUT155 2013-02-14 22:30:00 70.2 65.8 30.160 42 2.0 7.0 86 0.03 Cumulus v1.9.3
INEWSOUT155 2013-02-14 22:40:00 69.1 65.4 30.160 39 2.0 6.0 88 0.06 Cumulus v1.9.3
INEWSOUT155 2013-02-14 22:50:00 69.4 66.1 30.160 96 2.0 5.0 89 0.06 Cumulus v1.9.3
INEWSOUT155 2013-02-14 23:00:00 70.3 66.6 30.160 19 1.0 3.0 88 0.06 Cumulus v1.9.3
INEWSOUT155 2013-02-14 23:10:00 70.5 66.1 30.160 39 2.0 5.0 86 0.06 Cumulus v1.9.3
INEWSOUT155 2013-02-14 23:20:00 70.5 65.4 30.170 43 1.0 5.0 84 0.06 Cumulus v1.9.3
INEWSOUT155 2013-02-14 23:30:00 70.3 64.9 30.170 45 3.0 8.0 83 0.02 Cumulus v1.9.3
INEWSOUT155 2013-02-14 23:40:00 70.9 65.1 30.170 50 2.0 4.0 82 0.00 Cumulus v1.9.3

This shows non-zero rainfall amount/rate (0.06) from 2230z until 2330z with a tapering off of values (0.06 to 0.02 to 0.00) between 2320z and 2340z. This is a typical example of what happens every time it rains. Instead of sending zero rainfall at 2250z or 2300z, something somewhere sends the last rainfall amount/rate until the next hour.

Cheers,
Pat

[steve]

I must not have explained it very well, sorry. In the example you've just quoted, it stopped raining at around 22:50 UTC. The 'rainin' figure sent to WU is the rain in the previous hour. That means that if it stopped raining at around 22:50, the rain in the previous hour figure doesn't drop to zero until an hour later, around 23:50, which seems to be what actually happened.

If rain is recorded just before 22:50, that rain tip counts towards the total rain in the last hour until an hour has passed, so it counts until around 23:50.

Or am I missing something?

[pjwxman]

You explained it well.

I guess what bugs me is from a meteorological observations point of view, having a rainfall rate (per minute, hourly, etc.) be non-zero when nothing is falling from the sky seems wrong. If it rains at a rate of 0.6mm/hour between 08:00 and 08:07 and it stops raining at 08:08, I find it strange to say rain is (still) falling at a rate of 0.6mm/hour until 09:00 when the actual rainfall rate between 08:08 and 09:00 is in reality 0.0mm/hour - it stopped raining. Reporting a rainfall rate of 0.6mm/hour every 10 minutes until an hour has passed seems incorrect since noting is falling.

Tapering it off one observation before the hour ends seems even stranger. Why would it have dropped to say 0.2mm/hour between 08:50 and 09:00 when there is no precip? I really don't get that one.

Have a look at Jan 13th, 2013, it might make what I'm trying to day clearer. I was using WeatherLink back then - Cumulus is much better and preferred BTW! It rained a few times that day. The reported rainfall rates and graph are a good representation of the actual rainfall. When it stopped raining, the rainfall rate went back to zero, not an hour later.
http://www.wunderground.com/weatherstat ... 13&month=1

Maybe this bugs me because I've gotten so used to looking at observations (METAR, SPECI and 1-minute data when available) to do my job that I'm thinking of it more in terms of actual observations rather than "in the last hour." "In the last hour" would make sense if it wasn't a rainfall rate but an actual rainfall total for the hour, like airport observers report snow totals.

[steve]

I think WU have confused things by using the word 'rate', when it's actually the total rain in the previous hour. Yes, that could be regarded as a rate, but it's the average rate over the hour.

But note that tipping bucket rain gauges can't really tell you when it's stopped raining anyway, which is why the Davis rain rate calculation has a 'tapering off' factor built in to it, and the rate becomes zero 15 minutes after the last recorded bucket tip. The WU version effectively increases that 15 minutes to an hour.

[Spider-Vice]

It's weird because it also seems to depend on what the software sends to WU. This station uses WeatherLink and seems to send a "real" rain rate, which is probably averaged.

http://www.wunderground.com/weatherstat ... h=1&day=11

[steve]

The protocol spec is here: http://wiki.wunderground.com/index.php/ ... d_Protocol

It says that the rain in the last hour is to be sent.

[pjwxman]

Hello again Steve,

Thanks for pointing this out. I'll take the issue up with WU from now on. Sorry to have been a pain about this.

Cheers,
Pat

[pjwxman]

Here is the reply I got from WU:

Hello Patrick,

Thank you for your feedback. I took it to our director of technology, and he agrees.

We're thinking of changing the definition to "rainfall rate in/hr" -- instantaneous rainfall rate in inches per hour.

That way, the rate would drop to 0 when it stops raining, not minutes (up to 60 minutes later).

The difference being how the rate is calculated. The simplest way to calculate the rate is to use the rainfall in the past 60 mins (literally inches / hour), but meteorological, one wants the current rate but in the units inches/hour.

Regards,
William
Wunderground Support

[RayProudfoot]

Hi Pat,

Thanks for posting their response. There should be no 'thinking of changing' at all. What they show at the moment is clearly misleading and erroneous.

The problem with WU is there is no forum for discussing these types of things. If there were they would get a far better idea of user issues than with their current 'ticket' arrangement.

Hopefully they will make the change soon.