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CoCoRaHS

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IN-AL-39
In January 2010, I became part of the Community Collaborative Rain, Hail, and Snow (CoCoRaHS) Network and obtained the officially approved manually operated 4" rain gauge. It has always been attached to the same mounting post as the Davis Vantage Pro2, and both times on the easterly side of the post. The complete gauge sticks about 3" above the top of the green post (slightly above the top of the rain bucket). My CoCoRaHS station id is IN-AL-39 (i.e. the 39th CoCoRaHS rain gauge installed in Allen County, Indiana). In addition to rain, I also report snowfall, snow depth, and hail information to CoCoRaHS; all of which is archived on the CoCoRaHS website. Simply click on the View Data link near the top center of the webpage, pick the data set, and enter my station id to browse through all my reports.

Accuracy of Vantage Pro2 rain gauge

In use through June 2016, when compared to the co-located CoCoRaHS rain gauge, my original Vantage Pro2 rain gauge fairly consistently under-reported liquid precipitation by 10-15%, when water was able to flow freely. The discrepancy seemed to be largest during heavier rain events, so I believe there was some water loss as the tipping mechanism couldn't keep up. Additionally, in use until August 2014, the original rain bucket (which funnels rain into the tipping mechanism) would at times become clogged by leaves or bird droppings so that only a small amount of water would seep through into the tipping mechanism; and occasionally pine needles would lodge in the bottom hole in such a way as to redirect the stream of water through the bottom hole away from the tipping mechanism inside and cause the Vantage Pro2 to record zero precipitation when the CoCoRaHS rain gauge caught 0.25 or more inches.

Davis came out with an improved rain bucket in 2014 which has a leaf guard within to mitigate clogs/redirects and bird spikes to reduce droppings. Only on a couple of occasions since I installed that (in August 2014) did a narrow small leaf (from the neighbor's twisted willow tree) make it thru the leaf guard and block the bottom hole. I never again had bird droppings within the bucket.

With the current Vantage Pro2 (installed in July 2016), for the first couple of months the discrepancy appeared to be generally less, and was frequently spot on or even a 0.01" over the CoCoRaHS rain gauge catch. However, over the winter of 2016-2017, I have noticed occasions where the new Vantage Pro2 under-reports by as much as 10%.

There was a potential for some rain shadowing at the original location (i.e. prior to 29 July 2016); but as the CoCoRaHS gauge and Vantage Pro2 instruments were mounted on the same post, it would've affected both equally. The current location is as far from trees and buildings as possible on my property — the elevation angle to the two trees on either side (E/W) is closer to 50° than the ideal max of 45°, but the tops of the houses on either side (N/S) are about 40°.

None of the rain buckets have been heated, so precipitation amounts are unreliable during winter months. The first couple of years I had the Vantage Pro2, I even covered the rain bucket to keep everything out; but then decided some winter information was better than none and have left it uncovered since then. Still, as long as the temperature is below freezing, no precipitation amount will be recorded. Then, when it does warm up, the precipitation amount for that day will include the melted equivalent of whatever fell (and remained) in the bucket since the last time it was above freezing. Less than 4 inches of snow will fit in the rain bucket; and much of that often blows out or sublimates before it melts. Thus, even monthly precipitation amounts reported when frozen precipitation has occurred will usually be less than the melted equivalent of the actual precipitation for that month.

Bottom line, you will always get a more accurate picture of the precipitation that falls at my house by reviewing the CoCoRaHS data set.

CoCoRaHS Water Year Summary

These reports, generated by CoCoRaHS, provide summary data as well as every individual observation I reported during their Water Year (01 October through 30 September).

National Centers for Environmental Information

NOAA's National Centers for Environmental Information also maintains a history of the daily precipitation data I've reported through CoCoRaHS: IN-AL-39 Station Details. Unfortunately, they do not capture the multiday reports in any way.

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