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Old 02-26-2008, 10:05 AM   #1
BlackCatIslander
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Default Why the difference in readings?

I have noticed the temperature readings for Black Cat and Bear Island differ by two or more degrees and that the pressure readings also differ. Since they are fairly close, I would expect more uniformity. Just curious.
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Old 02-26-2008, 12:03 PM   #2
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Default Could be a bunch of things

Welcome to the world of science... or anything, for that matter: In theory things should always work a certain way, but in real life there are so many variabilities that they never do. In my high school (and college) science lab classes, no two sets of lab partners ever got the same results even when they followed the instructions equally well. And I don't think any lab class was ever able to make textbook situations become reality during an experiment. It just doesn't happen except by Divine intervention.

To make the most accurate comparison between two locations, one needs to install the same exact types of instruments, manufactured and calibrated at the same time to the same standard. They need to be installed to the same standard. Even then, there will be variability because no two locations are exactly alike, and all instruments are made by people (who are imperfect) which means that there has never been a perfect instrument; therefore every instrument has at least a tiny flaw somewhere, and that varies between instruments.

To get the most accurate comparison between pressure readings, the same 'old fashioned' kind of barometer must be used: The one that actually has 30 inches of mercury in it, instead of the kind that uses digital numbers to say "30.00 In/Hg". That's just because electronics are a lot more finicky than the old-fashioned technology they're based on. The old fashioned stuff is made to last, and the electronic stuff is made to be replaced. Every time I go hiking I meet up with people who get different readings on their GPS's while the magnetic compasses are all saying exactly the same thing.

As far as I know, Bear Island and I are not using the same instruments except for water temp. I installed mine to NOAA's standards (regulating where and how sensors are located) which is what most of us weather geeks try to do, so he may have done the same.

Between any two locations (especially here in New England) there are differences in sun exposure (north facing vs. south facing)and there are often differences in land features. For example a huge outcropping of boulders can gather and radiate heat in one neighborhood while a dense grove of pine trees can drop the temp by an equal number of degrees in an adjacent neighborhood (I have witnessed this kind of variability in the Boston suburbs.) For two equally-nearby weather stations in a place like Kansas, both locations would most likely be identical (and flat.)

This sort of thing is one reason why the computer models have such a hard time digesting and predicting New England weather.

It's kind of like the skier's question when spring rolls around: How can the snow be melting so fast from the Tuckerman Ravine Trail on Mt. Washington while Wildcat Mountain is still buried? The two locations are only a couple miles apart, and are at the same elevation, but oh what a difference they can have!

Last edited by CanisLupusArctos; 02-26-2008 at 12:38 PM.
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Old 02-26-2008, 01:53 PM   #3
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I think the problem is that I have a cheap weather unit. I get two air temp readings, one from the camera's add-on weather station and the other from the more accurate "Sensatronics" unit that also does water temp.

I have just changed the air temp display to the better unit. I expect those readings will be better in the future. Our water temp readings have alway been very close.

The barometer lost its altitude setting somehow, I have set it again and hope it works better. The humidity reading is just nuts.

Next summer I may move up to a better weather unit. I am also thinking about a remote operated pan and tilt camera. People can move the camera around while they watch. The main camera will stay fixed.
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Old 02-26-2008, 04:23 PM   #4
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Thanks for the responses CLA and Bear Islander. I sort of expected the explainations but I wasn't sure since we very grateful viewers do not know what equipment is giving us the readings. I want to thank you both and all the others who provide the pictures and info that we all enjoy.
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Old 02-26-2008, 05:32 PM   #5
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Quote:
Originally Posted by Bear Islander View Post
I think the problem is that I have a cheap weather unit. I get two air temp readings, one from the camera's add-on weather station and the other from the more accurate "Sensatronics" unit that also does water temp.
I didn't mean to say there was a problem, as scientific instruments of any type (cheap or expensive) can vary... and New England's often-localized weather just adds to the variations in weather readings between neighbors.

I have two temp probes side-by-side. The first is the one whose readings you see online. The second is made by the predecessor to Sensatronics, in the days before 'online.' Both are high quality probes and I paid just as much for each of them. Their readings sometimes deviate from each other by up to 2 degrees, and sometimes they read the same (as they are doing today).

In Boston there's a great weather instrument shop, Robert E White instruments, where I've made many purchases over the years. I remember once he steered me away from buying a more expensive instrument because it s accuracy didn't match its hype, and convinced me instead to go for something considerably cheaper, because he had found it to be more accurate. Scientific instruments are funny things!
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Old 02-27-2008, 09:36 AM   #6
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Thanks to both CLA and BI for your work keeping those instruments operating and being available for us to use.
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