Topic: Precise Rain Start/Stop Time Information Needed

[wxtech]

I'm using VWS V13.01 p09.  Is there a precise way to determine when rain started and stopped?  I use graphs vws744 annual rain accumulation & vws859 rain rate.  The graphs can't be magnified to an hourly view if the data is several hours past. 
Data file vws/data/daily/090802.txt shows data at 20 minute intervals.  By precise rain start/stop time, I mean to an accuracy of 5 minutes.
I go to Wunderground data table for rain occurrence times.  I revert to WeatherLink rain graph which shows rain rate @ time.
Is there a VWS tag for rain start/stop?  Or maybe a way to determine rain start time from existing tags. 

[sam2004gp]

I know this is not what you want to hear, but I have got around this by looking at my "Daily" file.  I have it updating every 5 minutes, and it shows the rain values for each time period, so basically the starts and stops

[Anthony]

Aside from setting you DB timer to update a 1 minute intervals. I can't think of another way you could be any more precise.

[wxtech]

OK.  I set the timer from 20 minutes to 5 minute interval.  It's updating @ 5s now.  That'll do it until a tag comes available.  Thanks
Al

[tomcj2]

On several occasions I have compared the start time of a rain event from my visual observation to the time reported by VWS.  During a light rain they can be off by 30 minutes;  5 to ten minutes for a heavy downpour.  It takes time to fill up the bucket until it makes its initial tip.

[wxtech]

On several occasions I have compared the start time of a rain event from my visual observation to the time reported by VWS.  During a light rain they can be off by 30 minutes;  5 to ten minutes for a heavy downpour.  It takes time to fill up the bucket until it makes its initial tip.

I've often thought of adding a moisture sensor as a rain detector.  Use it to set off an audible alarm to warn when the first few drops of rain fall.  Davis has a 'leaf moisture sensor'.

[tomcj2]

I've often thought of adding a moisture sensor as a rain detector.  Use it to set off an audible alarm to warn when the first few drops of rain fall.  Davis has a 'leaf moisture sensor'.

I could find little data about the leaf moisture sensor at the Davis site.  Do you know if one or two drops would trigger a response?

[neondesert]

I'm using VWS V13.01 p09.  Is there a precise way to determine when rain started and stopped?  I use graphs vws744 annual rain accumulation & vws859 rain rate.  The graphs can't be magnified to an hourly view if the data is several hours past.  
Data file vws/data/daily/090802.txt shows data at 20 minute intervals.  By precise rain start/stop time, I mean to an accuracy of 5 minutes.
I go to Wunderground data table for rain occurrence times.  I revert to WeatherLink rain graph which shows rain rate @ time.
Is there a VWS tag for rain start/stop?  Or maybe a way to determine rain start time from existing tags.  

SLOWeather Chris was working on a project a while back that may help you.  Only drawback is it isn't through VWS.

Here's a link to the WXForum thread: http://www.wxforum.net/index.php?topic=1428.0

[Wx4U]

I believe there is a device for you to check. Try this udl: (http://www.weather-above.com/Rain%20D%20THC238.html)
It is being used by a weather staion in the UK, http://northantsweather.com/wx24.html.
Hope this helps.
Bob

[wxtech]

The disdrometer thread is very interesting.  I read most and scanned some material.  It went from audible to visible detection.  Here is a slightly different visible method of rain detection that was mentioned in wx eqpt maint school.  Raindrops from a funnel pass through a kerosene layer.  The kerosene layer is observed by a light source/detector.  As the water passes through the oil, the transmissivity of the oil changes.  The amount of rain is determined by the change of oil density.  It was described as a 'rain rate detector'.
Light rain may produce discrete water drops in the oil.  Heavy rain may cause mixing of water/oil.
The first/last rain may be determined, or the rain rate.  The drop characteristics can not be determined by this method.
Also, retaining the oil may be a problem on draining.  A siphon method may work to pull water settled on the bottom of the tank.