Rain/Precipitation and CoCoRaHS

[PaulMy]

Looking at Ray's new post on his rain totals this year with interest as we've had both a record low monthly (May) and record high monthly (July) rain this year, and also learned that CoCoRaHS has a new Data Explorer so I took a look at my CoCoRaHS data reporting...

I started with CoCoRaHS February 2014 - daily manual reading of the 4" rain gauge and uploading to CoCoRaHS. In the winter we measure the daily new snow and its SWE (snow water equivalent) and the total snow on the ground. Once a week we take a core sample of snow on the ground and melt it for the SWE.
My station was CAN-ON-31 https://dex.cocorahs.org/stations/CAN-ON-31/
We moved to a new address in June 2019 just a few blocks away but that required a new station so now CAN-ON-784 https://dex.cocorahs.org/stations/CAN-ON-784/
I really love the information and charts that the Data Explorer provides.
p.s. Ignore the fact that CoCoRaHS USA has annexed Canada as a state of the USA

I haven't missed a day, but sometime when away overnight then we do a multi-day reading when we get back. CoCoRaHS does their annual totals from Oct 1 through Sep 30 by station so my old CAN-ON-31 covers the CoCoRaHS period Oct 1, 2013 through Sep 30, 2019 and my current CAN-ON-784 for the period Oct 1, 2018 through current so they show some missing days from before my first reading and after we moved, but the 2 combined cover every day. Of course I also have my Davis VP2 and Cumulus since October 2008. I do a spreadsheet comparing the CoCoRaHS 24 hour precipitation at 8:00 am and the VP2/Cumulus) today at 8:00 am plus the previous day since 8:00 am so I can compare the manual 24 hours vs tipping bucket for the same period. In the winter I use the daily snow readings for entering into the Cumulus Diary.

Is it worth doing a manual reading every day when you have an automated station??? For me it is as I have the automated station for uploading to my websites and to the various weather services, and also have a great comfort in knowing how accurate those published measurement were, or were not! And also the data can be of great help for climate watchers, farmers, conservation authorities, etc.

Five years ago we had some big rain outbursts in the summer and both my VP2 and CoCoRaHS readings were very close. It so happened that a contractor was doping some sensitive excavating close by the local Thames River for a new housing development and the high rain caused their erosion containment to overflow and spill into the river causing potential damage to sensitive water species. The governing authority was called in to investigate. The investigation led them to contacting CoCoRaHS Canada on what records they had for the period of that heavy rain. CoCoRaHS found that my station was the closest to the spill and the investigators then contacted me. While I had both VP2 automated minute-by-minute and CoCoRaHS manual data they could only consider the manual recorded data for any legal matter. This spring, 5 years after the spill, I was served a subpoena to attend as a witness for a trial that charged the contractor and the consulting engineer with negligence for permitting the spill (not taking all appropriate action to avoid it). Just a week before the trial the contractor and engineer plead guilty and I didn't need to go as a witness, but my CoCoRaHS data was the proof. An unexpected benefit for being a weather enthusiast and CoCoRaHS contributor.

Enjoy,
Paul

[HansR]

Thanks Paul for a really interesting story.
Also thanks for the CoCoRaHS data explorer of which I had never heard.

It leads me to an additional question as Canada has much more snow than others you may have dealt with it before.
Snow is also a type of precipitation and the water eventually - after melting - penetrates the soil or runs off to an effluent (stream or river ...)

How is snowlike precipitation taken up in the precipitation figures (e.g. the yearly rain number) as the soil is definitely soaked after the snow melt as if all that snowy water had felt in those few days in which it melts. Is that accounted for? Snow height has no meaning/relation to the rain while effectively it is the same: snow is a kind of delayed rain.

[PaulMy]

Hi Hans,
I don't know how EC handles or reports the snow water content or SWE, or even if they do but I did find this https://open.canada.ca/data/en/dataset/ ... cc0d8de305. The CoCoRaHS snowfall and snowpack collection helps in gathering the total precipitation, and what amount is still on the ground and not yet penetrated or evaporated. The snowpack and SWE is very helpful to conservation authorities in their planning for spring thaws and runoffs into the water streams when floods can create danger to both property and humans.

In my own Snow Page http://www.komokaweather.com/weather/snowindex.html I have the Canadian Climate Normals - 30 Year Average. I thought I had it updated for 1990 - 2020 but that might not have been available this past winter so will need to do that for the 2023-2024 season.

I don't have a heater on my rain gauge so in the winter snow may accumulate in the collector and eventually melt and show as rain. But actually that rain was from a previous day. Also when there is a lot of snow it will overflow the collector or blow away so the precipitation data from my weather station for January and February is not always correct. I could install a heater, or manually update my Cumulus records but that wouldn't correct the uploads to say WU, PWS, etc. CoCoRaHS does give me valid data.

Enjoy,
Paul

[HansR]

Hi Paul,

Thanks for the work you put into this, interesting study. I understand that the snow => water (mm) conversion is not a hot topic in Canada (and around the world. But I'll look at that conversion in that study you linked.

A heater in the in the rain gauge parallel to the manual snow registration might give exact conversion parameters.
Fifty years ago we used to have a lot of snow over here but I certainly haven't seen any for the last 20 years but from the perspective of tools we are building here maybe I should pay some attention. Water content of the soil is important.

Thanks again,