Author Topic: 24 hr FARS Night time temp read warmer ? UPDATED!  (Read 8184 times)

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Offline upweather

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24 hr FARS Night time temp read warmer ? UPDATED!
« on: November 05, 2009, 02:29:40 AM »
I live about .5 of a mile from a NWS remote station and i can check data online I 've only had my 6153 for about 2weeks now and noticed my night time readings are slightly higher most nights  but not all the time it's still close but i'm thinking the 24 hr fars is affecting the readings for instance last night the nws station reported 26.2 I reported 27.3 this is close but other nights its been 2.5 degrees  warmer. I've been compiling the highs and lows of both stations and looking into averages.. the NWS stations is about 40ft lower elevation and also open area.

I'm just looking for most accuracy Daytime temps for the 2 stations seem to be more consistant.

UPDATED  UPDATED
Recently I've been looking into this and have found my daytime temps nearly identical and night temps on my 6153 reading warmer. I figured out the nights my temps are off by 2-2.5 degrees are clear still nights. The nws station has five minute reports and hourly I researched and found the MMTS is very sensitive and even more so then the VP2 FROM OTHERS THAT HAVE COOP STATIONS. I've been only running 1 battery in my 24 hr fars and recently put in both. and lowered the iss to 5ft at the top of the shield. The low temps on the nws MMTS are just before sunrise and during a brief time I know with 1 battery there is minimal circulation at night and with 2 it's maximum I believe it's been lagging behind because comparisons on the 2 stations during a time of little temp change they are within .5 degree.. does anyone support my idea here ? I just completed the change and i'll keep everyine informed.

« Last Edit: November 12, 2009, 07:49:42 PM by upweather »
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Offline floodcaster

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #1 on: November 05, 2009, 06:44:15 AM »
the NWS stations is about 40ft lower elevation and also open area.

That doesn't sound like much but it can be a big difference with regards to temp comparisons...especially during a calm, clear night with much radiational cooling.
Bill


Offline Anthony

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #2 on: November 05, 2009, 07:51:42 AM »
If the station with the lower reading is higher and open and the station with the lower reading is lower and somewhat sheleterd. What you are observing would probably be normal. What you are observing fall into the catagory called micro climates.



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Offline d_l

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #3 on: November 05, 2009, 09:11:40 AM »
The 24-hr FARS makes the ISS more responsive to small changes in the air temperatures at night.  It wouldn't by itself raise the night time air temperature.

The night time temperature difference between your station and the NWS could possibly be explained by something as simple as the difference in mounting height above ground level or the vegetation underneath and surrounding each station or the nightly wind regime differences.  All of which boil down to microclimate differences.

You could always pull the batteries from your FARS to make it a daytime only FARS if you feel your night time temperatures aren't representative of your site.
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Offline meteolarissa

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #4 on: November 05, 2009, 04:29:57 PM »
hello from greece,

if you put ur station little lower u will get same or even lower temp than the other station.
dnt ever think to stop the 24hrs fan cuz i did it for a while and my readings were higher than my shelter wooden screen at about 1-1,5 degree celsioys.
now i wuk it 24hrs all are ok and the readings are almost same....
 :-) =D>
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Offline Bushman

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #5 on: November 05, 2009, 05:28:01 PM »
Unless you live at the remote NWS site, why care?  :) 
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Offline WeatherGoose

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #6 on: November 05, 2009, 05:47:37 PM »
As was said... The temp variations over even small distances can vary greatly at night.  The fact that you have the FARS running may in fact be providing you with a more accurate reading that this neighboring station you mentioned.  You may also be in a micro-climate that is causing the differences.

If I as in your place, I wouldn't worry about it.  Definitely not worth losing any sleep over.  ;)



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Offline upweather

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #7 on: November 05, 2009, 07:50:10 PM »
I also have the sensor 5 ft above grass as the NWS station.. I forgot to mention I had previous to this a PEET BROS ultimeter 100 they claim accuracy +_ .5 degree
It seemed to track closer for night time lows within .5 degree but usually alittle lower then the NWS station but i guess i do remember few times where the temp variation was greater. The whole thing started when we got snow the other night less then 1" and it was wind driven stuck to the ISS  the NWS station reported 32.2 and i was getting 33.4  The snow seemed to be more frozen then it would be at 33.4 The wind at the time was more calm under 6mph . I know im getting maybe to critical. any more input ??
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Offline WeatherGoose

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #8 on: November 05, 2009, 09:02:23 PM »
Like I said, it really is pointless trying to match your temp readings to another station unless it is literally sitting on top of yours.  ;)

Barometer and Relative Humidity are more something you want to try to get in line with another station IF you know that station is reporting accurate information.  Just because a station is a NWS reporting station does not automatically mean that what it is reporting is gospel.

For example... The NWS station down in Oakhurst Ca. (Davis VP2) is owned and operated by the NWS in Hanford Ca., but it is in a KNOWN micro-climate area.  Its overnight temps are a good 8-12 degrees colder than the majority of the Oakhurst area, but because the siting location needed to be a government owned property, the local Sheriff station was tapped to run it.  They didn't have any other location options.  This station is repeatedly getting RED Xs and Thumbs down by the MADIS QC system.

The lows are off enough that I contacted the NWS Hanford office and found out that they were aware of the problems, but as I said, they had no other siting options at the present time.

If they have a choice between several PWS stations in an area, they WILL go with the most accurate and reliable one. (uptime) My station is the official NWS reporting station for Bass Lake Ca., and I was chosen because my data IS the most accurate in the area they needed to cover and I had a significantly better uptime perentage than any other private station around here. (Thank you LWC!)

So... I do know a lot about this particular subject.  ;)


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Offline Bushman

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #9 on: November 05, 2009, 09:53:23 PM »
Old proverb:  "Man with two watches never knows what time it is."  :)
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Offline mmorris

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #10 on: November 05, 2009, 10:05:44 PM »
I also have the sensor 5 ft above grass as the NWS station.. I forgot to mention I had previous to this a PEET BROS ultimeter 100 they claim accuracy +_ .5 degree
It seemed to track closer for night time lows within .5 degree but usually alittle lower then the NWS station but i guess i do remember few times where the temp variation was greater. The whole thing started when we got snow the other night less then 1" and it was wind driven stuck to the ISS  the NWS station reported 32.2 and i was getting 33.4  The snow seemed to be more frozen then it would be at 33.4 The wind at the time was more calm under 6mph . I know im getting maybe to critical. any more input ??

If I read the accuracy of the temp peet bros the +-.5 is Celsius and +- 1*F  here is the link: http://www.peetbros.com/ULTIMETERSPECS.pdf
« Last Edit: November 18, 2009, 10:30:33 PM by mmorris »
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Offline upweather

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #11 on: November 05, 2009, 10:07:12 PM »
 :lol: thats funny  I guess i just wont bother with it any more I've heard of some people entering temp offsets but like it was said earlier maybe it's just different even with it being close.

Old proverb:  "Man with two watches never knows what time it is."  :)
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Offline upweather

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #12 on: November 05, 2009, 10:10:16 PM »
good catch I never noticed that ? All this time i was almost possitive it said *F

I also have the sensor 5 ft above grass as the NWS station.. I forgot to mention I had previous to this a PEET BROS ultimeter 100 they claim accuracy +_ .5 degree
It seemed to track closer for night time lows within .5 degree but usually alittle lower then the NWS station but i guess i do remember few times where the temp variation was greater. The whole thing started when we got snow the other night less then 1" and it was wind driven stuck to the ISS  the NWS station reported 32.2 and i was getting 33.4  The snow seemed to be more frozen then it would be at 33.4 The wind at the time was more calm under 6mph . I know im getting maybe to critical. any more input ??

If I read the accuracy of the temp peet bros the +-.5 is Celsius and +- 1*F  here is the link: http://www.peetbros.com/ULTIMETERSPECS.pdf
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Offline WeatherGoose

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #13 on: November 06, 2009, 02:00:54 PM »
:lol: thats funny  I guess i just wont bother with it any more I've heard of some people entering temp offsets but like it was said earlier maybe it's just different even with it being close.

Old proverb:  "Man with two watches never knows what time it is."  :)

Yep.

Here is the MADIS QC page to that NWS station in Oakhurst I mentioned:

http://weather.gladstonefamily.net/site/AT301

Heres Mine:

http://weather.gladstonefamily.net/site/D2149


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Offline upweather

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Re: 6153 24 hr fars Night time temp read warmer ?
« Reply #14 on: November 09, 2009, 07:58:08 PM »
I've been monitoring the highs and lows with my station and the nws remote station My daytime temps have been right on with this nws station and my lows lately have been up to 3.5 degrees warmer. always warmer ? Maybe my station just reads warmer all the time and the NWS station picks up higher daytime  temp reading due to no FARS ?  I went to look at the NWS station and I could actually see it from my location  a field and 1 row of spruce seperates us.When i had the peet bros station I was always 1 degree at the most different. I forgot to mention that before.
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Offline upweather

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #15 on: November 12, 2009, 07:56:04 PM »
UPDATED AT THE TOP OF THE PAGE.
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Offline d_l

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #16 on: November 12, 2009, 08:35:49 PM »
I see nothing wrong with the reasoning in your update.  Is it possible that your fan was stopping before daylight due to depleted voltage in the one battery?

Some experiments that I did on my rain heater today suggested that there is a convection effect with hot air blowing out the funnel and cold air drawing into the space under the rain collector through the tipping drains.  This air circulation would further minimize the heating of the radiation shield underneath.
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Offline Sebastopol Wx

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #17 on: November 16, 2009, 01:00:24 PM »
I'm at 240' elevation or so midslope on a gradual hill. When I travel 1/2 mile down the road the temperature often drops 2 degrees. It is not unusual for me to have no frost on the roof but houses less than a mile away have frost. I have a 1-2 mph downslope wind most nights that keeps things mixed. High temperatures are fairly uniform, however.
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Offline Mason

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #18 on: November 16, 2009, 04:07:33 PM »
upweather,

i have the 24 fars vp2 and also own a mmts through being a coop observer for the nws. there's no doubt the 24 fars reads warmer than the mmts on clear nights after the winds decouple. i have both temp senors mounted at the same height, less than 10ft from each other, and with the same ground vegetation for clear comparison. the average difference is around 1.5 degrees.  I've tried to offset my temperature on the vp2, but then my high temps are too low.  So yes, you're on to something.
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Offline upweather

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #19 on: November 18, 2009, 07:53:16 PM »
I'm still conducting my test and so far no change The other night NWS station had a low of 17.6 and i had 22.3 When looking at the hourly i was accurate most times but the low temp was within 1 hour where it ropped like a rock for a brief time my 6153 never recorded that. I'm quite frustrated at this point my day time high are all on par and some nights cloudy or windy . I live 8 miles from lake superior and my night lows are what they are getting at the lake shore NWS station which is always warmer this time of the year when the lake water is around 48 degrees...My peet bros station was always so much more sensitive with a steel probe sensor. and updates ever few seconds.



 
upweather,

i have the 24 fars vp2 and also own a mmts through being a coop observer for the nws. there's no doubt the 24 fars reads warmer than the mmts on clear nights after the winds decouple. i have both temp senors mounted at the same height, less than 10ft from each other, and with the same ground vegetation for clear comparison. the average difference is around 1.5 degrees.  I've tried to offset my temperature on the vp2, but then my high temps are too low.  So yes, you're on to something.
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Offline d_l

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #20 on: November 19, 2009, 11:31:22 AM »
Wouldn't the shield fins on the mmts chill by radiation to be colder than the ambient air temperatures on cloudless, windless nights and then cool the non-circulating interior air where the sensor is?  The night air on the 24 hr FARs is continually being drawn in and the radiative cooling of its interior sensor chamber by the shield plates would be minimized. This is the night time version of what happens in the sensor chamber during the day when it is exposed to the sun.

So if you are trying to measure the nighttime ambient air temperatures, the VP2 with a 24 hr FARS would be more accurate than the mmts. If you are trying to measure a nightime surface temperature, then the mmts would be more correct.  The VP2 would probably be in better agreement with the mmts if you removed the batteries and thus converted it to a daytime-only FARS.
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Offline upweather

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #21 on: November 23, 2009, 10:07:59 PM »
Well I took out the batteries in the FARS and since then i've only had one clear morning and i was within 1.2 degrees of the NWS station my day time highs are still on par. I'll keep you posted on my study..but so far i'm closer on my readings.. I'm only thinking now that why do i even have the 24 fars if im not using it. But i'd rather have more similar methods to the NWS in temperature recording ..What do you think???

Wouldn't the shield fins on the mmts chill by radiation to be colder than the ambient air temperatures on cloudless, windless nights and then cool the non-circulating interior air where the sensor is?  The night air on the 24 hr FARs is continually being drawn in and the radiative cooling of its interior sensor chamber by the shield plates would be minimized. This is the night time version of what happens in the sensor chamber during the day when it is exposed to the sun.

So if you are trying to measure the nighttime ambient air temperatures, the VP2 with a 24 hr FARS would be more accurate than the mmts. If you are trying to measure a nightime surface temperature, then the mmts would be more correct.  The VP2 would probably be in better agreement with the mmts if you removed the batteries and thus converted it to a daytime-only FARS.
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Offline d_l

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #22 on: November 23, 2009, 11:14:31 PM »
It appears that you might be close to matching the NWS readings and you might even have identical averages over a month-long period.  There still might be day-to-day differences due to microclimates.

I think I want my ISS measuring night time <u>air</u> temperatures. I think that is what the NWS has been "trying" to do all these years with cotton shelters and mmts units.  If they could have installed FARS on their stations before this, I think they would have.

But that is just my opinion. My temperature readings are very close (almost identical when corrected for the elevation difference) to those of a county-run weatherstation (it isn't a Davis station) on a golf course about a mile away.  I don't know if that station has a FARS because I haven't gotten close enough to it to tell.
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Offline upweather

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Re: 24 hr FARS Night time temp read warmer ? UPDATED!
« Reply #23 on: November 24, 2009, 12:54:25 AM »
I do believe there is some days where the micro climate should be taken into consideration. It its possible the colder air is sinking to the lower elevation about 40 ft.. this more evident when patchy frost would appear in the fall.  Could micro climate effect happen only at night? on clear still mornings? im assuming so . Maybe i will just run the 1 battery . my readings were not as far off like with the 2 batteries having more aspiration at night.


It appears that you might be close to matching the NWS readings and you might even have identical averages over a month-long period.  There still might be day-to-day differences due to microclimates.

I think I want my ISS measuring night time <u>air</u> temperatures. I think that is what the NWS has been "trying" to do all these years with cotton shelters and mmts units.  If they could have installed FARS on their stations before this, I think they would have.

But that is just my opinion. My temperature readings are very close (almost identical when corrected for the elevation difference) to those of a county-run weatherstation (it isn't a Davis station) on a golf course about a mile away.  I don't know if that station has a FARS because I haven't gotten close enough to it to tell.
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