Strange rainfall record

[insx]

Hi Folks

I have a new rainfall rate record this morning but how can this be?

Records: Hightest rain rate 93.6mm/hr 00:16 on 29 September 2012
Web page: Last rainfall 2012-09-28 16:47
(The web page has been updated today)

I'm assuming something is wrong, if so, how do I fix it and should I expect things like this often? The weather station (WH1081) has only been up for a week.

Cheers
Tim

[steve]

It's a common problem with Fine Offset stations, have a read through the forum. The rain counter jumps up by unlikely amounts. Cumulus tries to cope with the total figures, but you need to use the 'spike removal' settings on the calibration screen to stop the rate giving silly values.

Cumulus has built-in editors for highs and lows. For anything for which an editor isn't provided, stop Cumulus and manually edit the files. The formats are in the help and the wiki. Other than the highs and lows, assuming you do the changes today you will need to edit today.ini (correct the high rain rate figure) and perhaps Septlog12.txt if the rain rate figure made it in to that file.

[insx]

So I guess there's no point trying to make sense of how there could be a high rain rate when there has been no rain? It's just spurious data?

Is there any way to find out what the highest rain rate was before this happened? I will search the forum too.

[steve]

So I guess there's no point trying to make sense of how there could be a high rain rate when there has been no rain? It's just spurious data?

Yes. The rain counter in Fine Offset stations can increase even when there has been no rain. There are a number of ways this can happen, some 'physical', e.g. the wind blowing the gauge, and some 'electrical', presumably due to interference of some sort.

Is there any way to find out what the highest rain rate was before this happened? I will search the forum too.

Look in alltimelog.txt, or look in an old copy of alltime.ini in one of the backup folders; or get Cumulus to find the highest value from the logs using the editor.

[uncle_bob]

It's not just the Fineoffset that suffer this. Also the Lacrosse and all the similar (I guess re-badged) stations do it.
Normally it's the wind sensor that get ridiculous readings though.

Like Steve said, the Spike removal setting is your friend.

[insx]

I look forward to the dodgy wind readings then! I've put some values in the spike thing but of course I don't want to miss any extremes.

Thanks all

Tim

[senbrea]

I use a Fine Offset WH1080 rig. It is mounted at the very top of a 10ft aluminium pole which is affixed solidly to a 4 inch downpipe on the side of the house. on 22 Nov 2012 I got very high rain rates in the afternoon although it did not rain until later in the evening. During the afternoon we had winds gusting to 38 mph. It has been suggested that the erroneous rainfall rate in the afternoon might have been caused by the wind setting up a vibration in the pole which created a harmonic which caused the Reed Switch in the rain sensor to stutter over a considerable period of time. If that was the cause, I think I shall move the rain sensor to a point much closer to the lower end of the pole. Has anyone got any opinions on this problem?

[sfws]

If that was the cause, I think I shall move the rain sensor to a point much closer to the lower end of the pole. Has anyone got any opinions on this problem?

My opinion is 'go for low rain gauge'.

You are in the UK so Meteorological Office and Royal Meteorological Society advice is site rain gauge low and measure wind high - see http://www.rmets.org/weather-and-climat ... bserving-0.
For professional measurements it is the World Meteorological Office tighter guidance that is followed.

EDIT - 2 spelling corrections!

[senbrea]

Thank you very much for your suggestions. Your guidance is most welcome and I will move my rain sensor lower down. It will still be above the eave of the house, although still rather close, but there should still be a good catchment. Thanks also for letting me know about the Met. Office website. I shall go and study it carefully.

[daqddyo1]

My only spurious rainfall (13 mm) came on the sunny day that I installed my WS. I had plugged in the batteries and so the shaking of the unit off and on the pole gave me the bogus reading. I'll delve into the records as instructed in this thread and change the rain value to 0 for that day.

[insx]

I'm still confused by the rain gauge. I poured a very small amount of water into the gauge and it was clicking away and registering rainfall. We had a heavy shower today and it says today's rain is zero.

[mcrossley]

It requires a surprising amount of rain to constitute a single 0.3mm tip, a small shower may not be enough.

[insx]

There's definitely something wrong with my set up. It probably rained all night, there are huge puddles everywhere but Cumulus says we have had a 12 day dry period. Strangely, it says that the last rainfall was 3 days ago. No rain was registered in the last 24 hours. I'm off to pour some water into the gauge with it all connected.