Hi Henry. Thanks for joining our forum! It’s nice to have someone from Fine Offset/Ambient on the forum, providing feedback on our smart weather stations.
Looking at your data, this looks like the classic “rain on plate” issue - drops of water can interfere with the ultrasonic signal, creating erroneous readings. That was a relatively rare but still significant issue with early versions of our SKY device. There is quite a bit of discussion on the topic here on this forum.
For several months now, we have been applying a long-lasting superhydrophobic coating to the sonic reflector on all new SKY units which has virtually eliminated the issue. If you are experiencing this issue chronically, we would be happy to replace your SKY unit.