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I've got multiple mesonet sites around my property. They're 15 miles away in all directions, maybe a couple of them are a little more. ALL of them read very similarly on these hot afternoons we're having. Within 1 degree of each other, and dewpoints/RH are all pretty much identical. My VP2 with 24 hr FARS is right on the money with every measurement except dewpoint/RH. I'm getting readings that are consistently 4 to 6 degrees higher with dewpoint...and this in turn is throwing my heat index and THWS index readings into the stratosphere.
I've been dealing with this for a couple years but I'm finally tired of it. So I'm going to install a brand new SHT-31 sensor in my ISS sometime this week. I'm hoping this will correct the issue. I ordered a new filter cap also since it was just $3 bucks.
15 miles away is too far.
Not when you've got a half dozen sites that distance in all directions, and they all read identically on a stagnant summer day. The airmass is dead nuts consistent across the state on days like this.
Good luck changing your SHT31 if located within the VP2 that has a 24hour fan. This task requires the technician (user) to have slept well the prior night, patience, an uninterrupted 45-60 minutes, no nagging spouse, screaming kids or barking dogs, and a good roadmap on how to reassemble. I find this roadmap useful— https://www.scaledinstruments.com/wp-content/uploads/2023/07/24hr_fars_Exploded_Diagram-7-20-2023.pdf
Having a Teddy Bear nearby to squeeze when things don’t go well or you think you are done only to find screws leftover, can also be useful.
Interesting. I take my station apart every summer for cleaning of individual pieces. Never have had an issue so far. I'll keep this in mind, sensor should be delivered to me on Thursday.
As of right now, it's Noon EDT and showing a dewpoint of 80F. The mesonet sites surrounding me all show 73F. I'm hoping for better results with the new sensor.
Good luck. I had SHT31s in 4 separate ISSs last night and adjusted them to proper humidity. This morning, they were all reading high, as if I didn’t apply the offset, then about noon, the readings were acceptable. One of the 4 ISSs had a brand new SHT31 the other 3 were probably 2-3 years old. Bottom line, newest version didn’t help. To borrow a term from a former college professor, the design of the SHT31 is arguably “fundamentally flawed,” which is too bad as the rest of the Davis product is very good. A person just has to accept humidity-dewpoint readings from a SHT31 sensor are not reliable and move on with life.
If you guys are using a weather software program, you can get about a 90% solution. I think I used a 1.061x-5 correction to my outdoor humidity. It seemed to work well for the low and high end. A member here, ValentineWeather might have a recommendation too.