Weather Station Oddity

[Joey Ketcham]

Over the weekend I got the Oregon Scientific WMR-100 wireless weather station, it does great - during the day - with the conditions coming extremely close to the AWS weathernet station the local TV station has setup about 2 miles away...

But every night now since I got it the humidity on it jumps up to 83% and just sits there overnight, once the sun rises it goes back down to normal. It's done this is the 3rd night in a row it's done that.

Any ideas?

 

[Jeff Snyder]

It stays at exactly 83% for hours on end?

Local weather variability can be very high, particularly at night when the boundary layer decouples and local effects can be very significant (e.g. T varying over 10F across a 1 mile distance, etc). If it stays at the same value on several different nights, it's suspicious, I'd say. Does it ever go above 83% (maybe it erroneously tops out at 83%)?

 

[Joey Ketcham]

No, actually it's gone up since I posted this.. it's up to 94% now.

 

[Jeff Snyder]

I'd bet it's just evidence of local variability. The nearest obs I could find would seem to indicate that the temp near Pittsburg would be around 70-71, with the dewpoint near 62, putting the ambient RH in the 70%-75% range. But, the conditions at YOUR house may be quite a bit different, particularly if the land use, vegetation density, surface water density (and proximity to ponds, streams, lakes, etc), elevation, and other factors are different between your location and surrounding METAR locations.

Of course, this doesn't mean that something isn't wrong w/ your weather station, but the difference between your obs and nearby METAR obs, particularly at night, doesn't necessarily mean there's a problem.

What's the temp at this time, and does it agree w/ surrounding METARs? I suspect that your temperature is lower than nearby stations, which would help explain some of the higher RH (when combined with potential for higher surface moisture / Td at your location relative to nearby locations). It's really interesting to look at the OK Mesonet during times when local variability seems most pronounced (when local effects significantly modify the "ambient" or background environment), a situation that tends to occur most often at night w/ clear skies and calm winds.

 

[B Ozanne]

I have a Davis Vantage Pro that does a similar thing.

The dewpoint seems to "suck" up to the temperature every night. At least on any night where there is some moisture around. Then in the morning when the air dries they rapidly seperate. During dry periods everything seems accurate but when they get stuck together the Td is off.

 

[John Bowles]

I'm not familiar with the sensors on these, but as an amature astronomer I am familiar with telescopes dripping wet with dew on a long night. Could condensation effect the sensor reading?

 

[J Gontesky]

Sounds as straightforward as moisture condensing on the sensor as the temperature drops.