Dewpoint - Humidity - Massively Off

My AIR unit worked great all of last year and even through the winter. Then a few days ago the dewpoint just dropped off and is now no where close to accurate. I have the ASOS at my NWS office less than a mile from my house for easy comparison. The battery level still shows healthy, so that isn’t the issue. Any other ideas on what could have all of the sudden caused this change? My device ID for the AIR is 2754. Serial Number is AR-00004064.

Dew point is calculated from Temperature and Humidity. So is either one of those wrong?

The temperature is accurate. So in that case the issue lies with the humidity. Guessing the humidity sensor went bad. I am going to try putting in new batteries anyway tomorrow just to see if resetting it that way makes any difference.

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What are the humidity readings before and after the issue?

What is your station ID?

Humidity values were accurate earlier this spring with values in the 25-50% range. Now they are in the low single digits where actual values are in the 25-40% range. Was showing dewpoint values as low as near -30F the other day when actual values were in the teens above zero. The station is currently showing a RH of 7% (with a dewpoint of -13.7). Actual numbers from the ASOS just down the road are an RH of 25% (with a dewpoint of +12). My station ID is 1598.

The voltage on the Air is good. No need to replace the batteries.

Humidity readings vary from from 40% to 7%. The Temperature seems to vary normally.

It would seem your Air is in a very dry area.

If you think there is an issue, send an email to and ask that your data be examined for a possible hardware issue with humidity.

Funny that this just got posted. I was looking at my CWOP data and have the exact same problem. Station ID is 5448

Average humidity error -12.9 %
Error standard deviation 6.6 %
Worst average humidity error -17.4 %
Worst standard deviation 14.7 %
24 hours Day time Night time
Average dewpoint error -6.5 °F -8.1 °F -5.1 °F
Error standard deviation 3.2 °F 3.2 °F 2.5 °F
Worst average dewpoint error -9.8 °F -11.7 °F -9.6 °F
Worst standard deviation 6.3 °F 4.7 °F 9.3 °F

It is in a slightly drier location than the ASOS, but no where near what the readings are currently showing. I will take it up next to the ASOS for a time when I get a chance and verify it is reading far too low. After that I will send an email to Thanks for looking into this.

It could be you need the humidity sensor calibrated. Let’s hope it’s something simple.

Maybe, if you take the Air indoors for some time it will come back to normal operation.
It is reported, it would help in some cases of humidity sensor errors.

That generally only works if the humidity is too high. He is reporting that humidity is too low.

Update on the humidity sensor. It appears to have resolved itself, but the how is quite strange. I planted new grass in the area and set up my sprinkler and watered the grass. The sprinkler got the AIR wet through the vents of the radiation shield. Once the air got wet, the humidity sensor appears to have somehow corrected it self and it now matches the ASOS almost perfectly.

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And another update on the humidity sensor, it has gone berserk again. Seems to be okay at night, then as soon as afternoon comes around it absolutely tanks. I have verified with other instruments the dewpoint at my house is very similar to the ASOS just down the road. The humidity sensor will calculate dewpoints 30-60+ degrees too low and then this afternoon it just hit 0F and isn’t moving anymore with a “nan” being spit out.

I think you may actually have a defective humidity sensor. I suggest you email

FYI for others. The humidity sensor does not calculate the dew point. The dew point us calculated in the phone and web applications with a formula using temperature and humidity.

I will do that. Thanks, Gary.

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