Dear WeatherCat users who are fussy about measuring how much precipitation has fallen,
One of the new features of WeatherCat 3.0 (released March 2018) was RAINSTORM period for the STAT$ tag. This allows you to create tags describing the conditions of a storm. I use this feature extensively in my Storm Status Custom Text Window that is described here:
https://athena.trixology.com/index.php?topic=2689.msg26014#msg26014You can even download a copy to install on your WeatherCat installation.
As described on the WeatherCat manual (on page 213) the RAINSTORM period is defined as the time between the first measurable rainfall rate and now. It becomes undefined if there hasn't been any measurable rainfall in 24 hours.
Those of us with Davis Vantage stations have access to another attempt to track the total amount of rain from a storm. Looking at that manual (page 23 in mine) Davis defines a storm (and I quote:)
"It takes 2 tips of the rain bucket to begin a storm event and 24 hours without rain to end a storm event."When Stu released WeatherCat 3 he explicitly warned us that WeatherCat and Davis consoles would disagree from time to time based on their different definitions of a storm. Most of the time, WeatherCat will "underreport" a storm in situations where the storm starts with a lot very light rain or drizzle that doesn't produce a measurable rainfall rate.
The difference in perspectives I think can be easily understood by where the two definitions were created. At the time, Stu was in Scotland where it can be "moist" for many days at a time. In such cases the Davis console will fail to clear in between storms so long as so little as another hundredth of an inch of moisture is detected. For people living in such areas that makes the Davis definition not very useful.
On the other hand, the engineers of Davis Instruments are based in arid Northern California and the problem is drought. From their perspective, drizzle is most definitely counted since that too will stop quickly - at least usually.
I don't live far from Davis Instruments and my weather station was able to show why Stu's definition is in some cases better. Last Sunday into Monday we had another atmospheric river event and received over 4" of rain. That unfortunately caused some flooding in our workshop. We mostly had a break on Tuesday, but did get a small amount of drizzle. Wednesday night into Thursday we got another storm. Thursday morning, WeatherCat reported the following for the storm:
On the other hand, my Davis console was "confused" by the drizzle and instead reported that we had endured one very long storm:
Thankfully, the Davis console was wrong. I did get enough of a break to clean up after the flooding over the weekend. Alas, the WeatherCat report indicated another substantial amount of rain had fallen overnight - enough to bring in more flooding in spite of my attempts to redirect the source of water.
Until now I had been siding with the Davis engineers, mostly because I wanted to count every drop! I have since been persuaded that WeatherCat has the better implementation of storm period. Nonetheless, as this exercise has demonstrated, how one goes about defining a storm purely from weather instrument data is anything but clear!
Cheers, Edouard