Topic: False humidity spike?

[WxLover16]

I just noticed that my humidity spiked from 52% to 64% in about 5 minutes but has since dropped back to 56%. I haven't noticed this kinda spike/fluctuation since I got my station back in February. Do I have a faulty humidity sensor or are these accurate spikes? The weather is partly cloudy, humid and hot if that helps. Usually you only see humidity spikes like that in very dry air. All the while, the temp has stayed put around 90F.

[CW2274]

I just noticed that my humidity spiked from 52% to 64% in about 5 minutes but has since dropped back to 56%. I haven't noticed this kinda spike/fluctuation since I got my station back in February. Do I have a faulty humidity sensor or are these accurate spikes? The weather is partly cloudy, humid and hot if that helps. Usually you only see humidity spikes like that in very dry air. All the while, the temp has stayed put around 90F.

At 90F temp your dew went from about 70F to 77F (gawd, just shoot me) which is perfectly reasonable and occasionally expected. Relax.

[WxLover16]

I just noticed that my humidity spiked from 52% to 64% in about 5 minutes but has since dropped back to 56%. I haven't noticed this kinda spike/fluctuation since I got my station back in February. Do I have a faulty humidity sensor or are these accurate spikes? The weather is partly cloudy, humid and hot if that helps. Usually you only see humidity spikes like that in very dry air. All the while, the temp has stayed put around 90F.

At 90F temp your dew went from about 70F to 77F (gawd, just shoot me) which is perfectly reasonable and occasionally expected. Relax.

lol yeah summer in the south doesn't feel too good here. It seems the humidity is steadier now than it was. Hopefully just a normal spike.

[CW2274]

As I've stated many times before, the 31 in an aspirated VP2 can snap your neck with its response.

[WxLover16]

As I've stated many times before, the 31 in an aspirated VP2 can snap your neck with its response.

Hey as long as it's just the 31 being sensitive and not an inaccurate reading I'm all for the variance. Just didn't expect it and was hoping it hadn't become faulty. I'm back up to 75dp 64% humidity at 89.1. Sauna like. Also just checked and the 77dp I recorded earlier was the highest of the summer so far. Ugh.

[dendrite]

I do 10-15% swings sometimes in 1 minute. It happens...especially with stronger aspiration, transpiration, and weak winds (poor mixing).

[WxLover16]

I do 10-15% swings sometimes in 1 minute. It happens...especially with stronger aspiration, transpiration, and weak winds (poor mixing).

Wow. Well I guess that explains it. Just extremely erratic (yet accurate) with the SHT31. Winds were very weak at the time.

[WxLover16]

The SHT31 is supposed to be more accurate yet there's been a few mornings lately where visibility has been near 0 with fog and my humidity has not gone above 98%. Should I offset it by 2% or just leave it. Has anyone else had this problem with thick fog and a humidity not at 100% with the 31? Humidity isn't nearly as big of a deal to me as is temperature, but was just wondering. Going back in the historic data on my console, the highest my station's humidity has gone is 99% with a low of 10%, quite the spectrum.

[floodcaster]

The SHT31 is supposed to be more accurate yet there's been a few mornings lately where visibility has been near 0 with fog and my humidity has not gone above 98%. Should I offset it by 2% or just leave it. Has anyone else had this problem with thick fog and a humidity not at 100% with the 31? Humidity isn't nearly as big of a deal to me as is temperature, but was just wondering. Going back in the historic data on my console, the highest my station's humidity has gone is 99% with a low of 10%, quite the spectrum.

Just switched to the SHT31 today with my VP2+ with 24 hr FARS and will be curious to see my dp/RH during fog events. My original sensor never got above 98% and most of the time never above 97%. I don't recall 100% since my old WMII. Regarding the spikes, they do seem more pronounced than before under certain wx conditions as mentioned already. Wonder if there is any software that will calculate a running 5min average temp and dew point similar to ASOS?

[dendrite]

I've seen M1/4SM at the local ASOS with a 2F dewpoint depression. I wouldn't read too much into it. My SHT31 hit 99% last night after a cool, rainy day. Twice I've seen it hit 100%, but it's been a little over a month since it has happened. I wouldn't adjust it.

[BigOkie]

I've seen M1/4SM at the local ASOS with a 2F dewpoint depression. I wouldn't read too much into it. My SHT31 hit 99% last night after a cool, rainy day. Twice I've seen it hit 100%, but it's been a little over a month since it has happened. I wouldn't adjust it.

Running a 24hr FARS unit makes it nearly impossible for me to hit 100 percent humidity.  The highest I've ever gotten is 99 percent, and that may have been during a time where my fan wasn't running due to failure.  The highest I see it run when I know it's running is 98 percent.

[dendrite]

I've seen M1/4SM at the local ASOS with a 2F dewpoint depression. I wouldn't read too much into it. My SHT31 hit 99% last night after a cool, rainy day. Twice I've seen it hit 100%, but it's been a little over a month since it has happened. I wouldn't adjust it.

Running a 24hr FARS unit makes it nearly impossible for me to hit 100 percent humidity.  The highest I've ever gotten is 99 percent, and that may have been during a time where my fan wasn't running due to failure.  The highest I see it run when I know it's running is 98 percent.

I have a 24/7 12V fan that pulls about 50CFMs. I have no problem hitting 99%.

[CW2274]

The SHT31 is supposed to be more accurate yet there's been a few mornings lately where visibility has been near 0 with fog and my humidity has not gone above 98%. Should I offset it by 2% or just leave it. Has anyone else had this problem with thick fog and a humidity not at 100% with the 31? Humidity isn't nearly as big of a deal to me as is temperature, but was just wondering. Going back in the historic data on my console, the highest my station's humidity has gone is 99% with a low of 10%, quite the spectrum.

Up to you, but I'd leave it alone. My 31 has gone from a high of 98%, to a low of 1%, many times.

[CW2274]

The SHT31 is supposed to be more accurate yet there's been a few mornings lately where visibility has been near 0 with fog and my humidity has not gone above 98%. Should I offset it by 2% or just leave it. Has anyone else had this problem with thick fog and a humidity not at 100% with the 31? Humidity isn't nearly as big of a deal to me as is temperature, but was just wondering. Going back in the historic data on my console, the highest my station's humidity has gone is 99% with a low of 10%, quite the spectrum.

Wonder if there is any software that will calculate a running 5min average temp and dew point similar to ASOS?

There is not.

[WxLover16]

The SHT31 is supposed to be more accurate yet there's been a few mornings lately where visibility has been near 0 with fog and my humidity has not gone above 98%. Should I offset it by 2% or just leave it. Has anyone else had this problem with thick fog and a humidity not at 100% with the 31? Humidity isn't nearly as big of a deal to me as is temperature, but was just wondering. Going back in the historic data on my console, the highest my station's humidity has gone is 99% with a low of 10%, quite the spectrum.

Up to you, but I'd leave it alone. My 31 has gone from a high of 98%, to a low of 1%, many times.

Yeah, I'm gonna leave it alone. 2% difference is not big enough for me to tamper with, especially with the 31 being so much better than the previous sensors, and anyway it has been up to 99 Now if it were the temperature sensor needing an offset, that's a different story.

[dendrite]

I've seen M1/4SM at the local ASOS with a 2F dewpoint depression. I wouldn't read too much into it. My SHT31 hit 99% last night after a cool, rainy day. Twice I've seen it hit 100%, but it's been a little over a month since it has happened. I wouldn't adjust it.

Running a 24hr FARS unit makes it nearly impossible for me to hit 100 percent humidity.  The highest I've ever gotten is 99 percent, and that may have been during a time where my fan wasn't running due to failure.  The highest I see it run when I know it's running is 98 percent.

I have a 24/7 12V fan that pulls about 50CFMs. I have no problem hitting 99%.

Pretty swampy out there right now for NH standards. I'm flatlined early this evening at 99% RH and would be shocked if I don't touch 100% tonight (unless the wind picks up and we mix out a bit).

Here's my raw wxlink obs for those who want to see an SHT31 hit triple digits RH. (

http://www.newenglandwx.com/northfield-nh/downld02.txt

[CW2274]

I've seen M1/4SM at the local ASOS with a 2F dewpoint depression. I wouldn't read too much into it. My SHT31 hit 99% last night after a cool, rainy day. Twice I've seen it hit 100%, but it's been a little over a month since it has happened. I wouldn't adjust it.

Running a 24hr FARS unit makes it nearly impossible for me to hit 100 percent humidity.  The highest I've ever gotten is 99 percent, and that may have been during a time where my fan wasn't running due to failure.  The highest I see it run when I know it's running is 98 percent.

I have a 24/7 12V fan that pulls about 50CFMs. I have no problem hitting 99%.

Pretty swampy out there right now for NH standards. I'm flatlined early this evening at 99% RH and would be shocked if I don't touch 100% tonight (unless the wind picks up and we mix out a bit).

Here's my raw wxlink obs for those who want to see an SHT31 hit triple digits RH. (

http://www.newenglandwx.com/northfield-nh/downld02.txt

I actually spent 15 minutes trying to figure out what I was seeing, that was painful. If I saw correctly at the bottom, you've several instances where the temp and due match exactly, yet only show 99%. No?

[dendrite]

I've seen M1/4SM at the local ASOS with a 2F dewpoint depression. I wouldn't read too much into it. My SHT31 hit 99% last night after a cool, rainy day. Twice I've seen it hit 100%, but it's been a little over a month since it has happened. I wouldn't adjust it.

Running a 24hr FARS unit makes it nearly impossible for me to hit 100 percent humidity.  The highest I've ever gotten is 99 percent, and that may have been during a time where my fan wasn't running due to failure.  The highest I see it run when I know it's running is 98 percent.

I have a 24/7 12V fan that pulls about 50CFMs. I have no problem hitting 99%.

Pretty swampy out there right now for NH standards. I'm flatlined early this evening at 99% RH and would be shocked if I don't touch 100% tonight (unless the wind picks up and we mix out a bit).

Here's my raw wxlink obs for those who want to see an SHT31 hit triple digits RH. (

http://www.newenglandwx.com/northfield-nh/downld02.txt

I actually spent 15 minutes trying to figure out what I was seeing, that was painful. If I saw correctly at the bottom, you've several instances where the temp and due match exactly, yet only show 99%. No?

heh...is the formatting messed up for you? Do you have word wrapping on in your browser? In firefix you can easily switch to the basic page style which gives you the horizontal scroll. They weren't matched exactly. The first line is the temp at time of ob, then the high temp over the past minute, the low over the last minute, RH, and then the calculated dewpoint.

Right on cue, 100% never happened. Some slightly drier air worked in. I thought something was wrong when I woke up because there's still some fog at tree top level, but a few other stations fell from 98-100% to 93-95% as well.

[floodcaster]

The SHT31 is supposed to be more accurate yet there's been a few mornings lately where visibility has been near 0 with fog and my humidity has not gone above 98%. Should I offset it by 2% or just leave it. Has anyone else had this problem with thick fog and a humidity not at 100% with the 31? Humidity isn't nearly as big of a deal to me as is temperature, but was just wondering. Going back in the historic data on my console, the highest my station's humidity has gone is 99% with a low of 10%, quite the spectrum.

Just switched to the SHT31 today with my VP2+ with 24 hr FARS and will be curious to see my dp/RH during fog events. My original sensor never got above 98% and most of the time never above 97%. I don't recall 100% since my old WMII. Regarding the spikes, they do seem more pronounced than before under certain wx conditions as mentioned already. Wonder if there is any software that will calculate a running 5min average temp and dew point similar to ASOS?

Just had my first 99% humidity reading today. So far I've been pleased with the performance of the new SHT31 and am glad I upgraded.

[WxLover16]

The SHT31 is supposed to be more accurate yet there's been a few mornings lately where visibility has been near 0 with fog and my humidity has not gone above 98%. Should I offset it by 2% or just leave it. Has anyone else had this problem with thick fog and a humidity not at 100% with the 31? Humidity isn't nearly as big of a deal to me as is temperature, but was just wondering. Going back in the historic data on my console, the highest my station's humidity has gone is 99% with a low of 10%, quite the spectrum.

Just switched to the SHT31 today with my VP2+ with 24 hr FARS and will be curious to see my dp/RH during fog events. My original sensor never got above 98% and most of the time never above 97%. I don't recall 100% since my old WMII. Regarding the spikes, they do seem more pronounced than before under certain wx conditions as mentioned already. Wonder if there is any software that will calculate a running 5min average temp and dew point similar to ASOS?

Just had my first 99% humidity reading today. So far I've been pleased with the performance of the new SHT31 and am glad I upgraded.

99%'s have been few and far between for me and still no 100% but I'm still satisfied with how good the sensor and response time is.

[SpartanWX]

I've seen M1/4SM at the local ASOS with a 2F dewpoint depression. I wouldn't read too much into it. My SHT31 hit 99% last night after a cool, rainy day. Twice I've seen it hit 100%, but it's been a little over a month since it has happened. I wouldn't adjust it.

Running a 24hr FARS unit makes it nearly impossible for me to hit 100 percent humidity.  The highest I've ever gotten is 99 percent, and that may have been during a time where my fan wasn't running due to failure.  The highest I see it run when I know it's running is 98 percent.

I run a 24 hour FARS and have hit 100% several times in the last few months since I upgraded the sensor.  I'm right next to a wooded stream valley though which makes it particularly soupy around here in the summer.

Related to the OP, I did have an unusual and unexplained midday 3 degree drop down and back up again in the space of 2 minutes.

http://www.wxforum.net/index.php?topic=30086.msg296401#msg296401

[alexstaar]

My SHT31 in a 24 hour FARS has hit the 99% mark 3 times since mid-April of this year. We haven't had any thick fog in that time period though. I think due to my location in an urban/suburban area makes it a bit more difficult to reach those types of extreme RH values often. Really wanting to have a thick fog soon so see how quickly it reaches 99% or 100%, but we haven't had one since February or March. The three 99% readings were during the overnight hours after a heavy rain (the previous day) in an already humid environment with dewpoint values around 70º.

[WxLover16]

Tonight is quite possibly a night where my 31 might come close to 100% humidity. Currently it's at 97/98%. Highest it's ever been is 99%.

[alexstaar]

We had a heavy rain shower move through this evening. My SHT31 has been sitting at 97% for the last 3 hours and hasn't moved. I'm surprised it hasn't got 98% yet. Everything outside is still wet from the rain several hours later.

[dendrite]

We had a heavy rain shower move through this evening. My SHT31 has been sitting at 97% for the last 3 hours and hasn't moved. I'm surprised it hasn't got 98% yet. Everything outside is still wet from the rain several hours later.

I just clicked the link in your sig. IT looks like you're at 98% now.