Dew point higher than my temperature

I believe my humidity and dew point sensor need adjusting.

Dew point Should never be higher than air temperature. Even if the temperature is rounded up. Please fix this.

eh… if temp is rounded up, dew point equals temp, it isn’t higher. Actually it might be that the real dew point is 67.5, but rounded up and shown like 68

Then they should have relative humidity 100%. My humidity has never been 100% in over 15 months

I looked it up. Actually the dew point was 67.5 (lower then temp)

with dew point 67.5 and temp 67.8 the RH should be 99% not 100% (try it here

I’m curious having air unit never had 100% rh Ever

it’s normal not having 100% humidity, If you had, it would basically mean that water is forming in mid air :slight_smile:

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Same here about humidity readings. I have an air blown psychrometer and when it indicates 99 to 100%,
the highest the Tempest goes is 92%. In my own home made WF scripts using UDP data, I was able to correct it using a simple calculation but, that doesn’t help with the Weatherflow live error.

FWIW my Tempest is currently reading 100% RH and I can see the mist forming outside.


there is some calibration done automatically by weatherflow for the RH, but if that fails in your specific situation, you might just ask them to do it manually. No need for a special script.

I placed the fan aspirated psychrometer at the Tempest for 30 minutes to see what I got plus my Davis station already indicating 99% and the local airport the same but the Tempest has yet to go higher the 92.23%. I guess that’s the luck of the draw in todays electronic sensing.

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Ok temperature and dew point are equal. Why isn’t humidity 100% calibration needed!

Station 8254

because they were not exactly equal. The temp was 70.0, but the dew point was 69.7 (which is shown rounded up to 70). Please look at your graphs. There you can see the extra decimal you need to confirm this. Putting 70 an 69.7 in the RH calculation gives a humidity of 99%. So everything is fine.

My own opinion is and will always be… When you buy something, it should work without constant concerns of accuracy or performance. Walking down to the unit, breaking down the mast and rebooting, and then re-installing and re-aligning it, I am almost ready to throw in the towel.
I have a Davis Vantage unit and never in 12 years has it been rebooted.

part of the idea behind the tempest is that it should be better, because it can be calibrated, as a constant process. How good that is, is a different question (and I personally sometimes doubt if that is a good thing in the first place) but having a RH value within 1% of what you expect, seems pretty accurate to me. (that’s pcappaccio’s unit). You think yours is a bit off. As mentioned it should calibrate automatically over time and you don’t have to do anything to make that happen.

Yes, 1% RH accuracy would be great however, mine only ranges from 40% to 92.25. When the humidy is 99% mine only registers 92.25 at most. I was working just fine until a week ago. My issue is the fact that one must go through a lot of trouble when the outdoor machine requires a reboot. When I installed mine, I wasn’t anticipating a complete disassembly of the outdoor mast just to reboot.

it shouldn’t need a reboot to get RH back in check. Perhaps the automatic calibration didn’t work as expected. it might need a manual override from weatherflow. Also, as long as it still is communicating, it can be rebooted remotely by @eric or weatherflow. (Just for the peace of mind it would be nice if a user could reboot his own system, but currently you can’t)

The reality is that that isn’t going to be the case. If the humidity always stayed below 60% or so, then the calibration on a sensor will stay quite consistent but at high humidity it can deviate. Basically, right now it is impossible to have a RH meter outside in the full range of RH and not have it drift. Just because a unit has no way to be recalibrated doesn’t mean it doesn’t need to be recalibrated.

Oh well, I guess here in the 21 century technology is going backwards. I had my Davis for over a decade and it doesn’t drift. Oh well, Thanks!

How do you know? I’ve read otherwise.

I have an fan aspirated psychrometer with wet bulb / dry bulb. I use it to compare between extremes of high humidity, around 50% and in winter I check low humidity extremes. I have never seen beyond 3 to 4 percent differences. At this point I see only 92.25 percent max over hours when the actual is 99 to 99.5. I have never seen 100% with any psychrometer.
I write my own code in Perl. Using UDP, raw data is vital to accuracy when calculating Mixing Ratio, Dew points and all those other thingys. I have been coding since the late 1970’s and pretty much understand the formulas. Anyway, right now all calculations are pretty much useless.
Thanks and have a nice evening.

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