I got my Tempest yesterday and got it set up temporarily in the back yard about 10 feet from my Stratus rain gauge. In the late evening, radar was saying I was getting rained on, but that was incorrect. There was enough water to barely collect a few drops of water on the Tempest dome, and not enough water to cause any drips through the Stratus funnel. The Tempest did record two “Very light” rain events with 0 accumulation. Since those events happened after I observed the water on the dome, I almost think the events resulted from agglomerated drops rolling off the dome and changing the load profile on the sensor. Today Rain Check boosted my total to 0.03". Bah. I figure the most I could have gotten was 0.005".
Today, Isiais made life interesting. When I got to the Stratus around 9am, it was just about to start overflowing into the outer cylinder – so somewhere between 0.99 and 1.01", depending on surface tension and funnel base volume. The Tempest said 0.97". Pretty good. When the Tempest got to 4.83", I measured the collected amount and got 4.90", but I had spilled a little pouring between the big cylinder and the calibrated cylinder (maybe not quite 0.1"). And between the Tempest reading of 4.83" and 4.90" at the end of the storm, I measured 0.07" in the Stratus. I would not be able to see a 3% variation at that level. So, overall the Tempest seems to read about 3% low over 0-5 inches of rain with multiple levels of rain intensity, but not much wind.
My rain gauge and Tempest are about 20 feet from the house, and 20 feet from the trees on the other side. Open view of the sky, but quite protected from wind near the ground (5 feet or so). The highest wind gust the Tempest measured during the storm was only 13 mph, so pretty quiet back there. The center of Isiais ran by about 20 miles east of my house.
If the Tempest keeps doing this well when I get it mounted over the end of the garage peak (a lot more wind), I’ll be able to retire the Stratus gauge.