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General Weather Discussion / Re: Solar Eclipse
« Last post by Steve on Today at 05:02:13 AM »
Temperature drop: Start at 1:09, peak at 2:31 with 80% eclipse. Partly cloudy skies. About a 5 drop.



Solar Radiation over the same time period. Around 4, the sun starts to go behind some trees; hence the big drop there.

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General Weather Discussion / Interesting (Re: Solar Eclipse)
« Last post by elagache on Yesterday at 11:12:38 PM »
Dear Alan and WeatherCat observers of natural phenomena,

Here's a couple of graphs where we had about 75% partiality.

Interesting!  That's a significant drop in temperature especially in the middle of the day.  I assume that skies were absolutely clear so that there was efficient radiational cooling.

Anybody else have some interesting WeatherCat eclipse data that they would be willing to share?

Cheers, Edouard
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General Weather Discussion / Re: Solar Eclipse
« Last post by awilltx on August 21, 2017, 11:10:26 PM »
Here's a couple of graphs where we had about 75% partiality.


Alan
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General Weather Discussion / "Total eclipse" by reason of fog. (Re: Solar Eclipse)
« Last post by elagache on August 21, 2017, 10:54:06 PM »
Dear Blick and WeatherCat eclipse phenomena observers,

We had a 95% partial eclipse here in Northern Utah.

Thanks for sharing the photo.  I thought it would be just as interesting to look at how the eclipse was effecting the environment as the eclipse itself.  Actually we had a 100% eclipse . . . . of the eclipse!  The fog was so thick that the disk of the sun was never visible.  Also The fog dispersed the light so evenly that even at 80% eclipse, you really couldn't notice it.  My webcam didn't show any noticeable effect, so there is no point in posting it.  I do have two graphs that are a bit interesting.  Even with the fog, the solar radiation was noticeably diminished:



The eclipse here was from roughly 9am to 12 noon with the peak at 10:20.  Also there is a leveling off in temperatures that you can see on this graph:



Beyond that, the eclipse was a complete bust in the foggy San Francisco bay area.

Cheers, Edouard
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WeatherCat Integration / Confused round #2 (Re: AWEKAS)
« Last post by elagache on August 21, 2017, 10:43:37 PM »
Dear Blick, TechnoMonkey, and WeatherCat troubleshooters,

Just talked to Davis tech support. If you enter your elevation in the Davis setup screen, the pressure is adjusted for altitude and gives you the "altimeter setting" reading. If you do not enter an elevation, the pressure is not adjusted for altitude and gives you the "sea level" reading. According to Davis, both methods are used and you pick the one you want.

But wait a minute, that just doesn't make any sense.  ??? Without the elevation the station cannot make any correction - how could it?  So this has to be reversed.  If you don't put in the elevation, then it reports the raw pressure that the sensor reports - whatever your elevation.  If you provide the elevation, the console can then compute the weight of the column of air that would exist where the pressure you are reporting at your elevation, would be at sea level.  It then adjusts the pressure for that additional weight of air.  That has to be how it works.

Personally, I have entered the elevation so my station should be reporting the pressure as if I was at sea level.

Cheers, Edouard
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General Weather Discussion / Solar Eclipse
« Last post by Blicj11 on August 21, 2017, 08:53:28 PM »
We had a 95% partial eclipse here in Northern Utah. Shadows cast by the eclipsed sun were very odd, and circular. The temperature dropped 8F in the hour preceding the highpoint (darkpoint) of the eclipse, which occurred at 11:35 AM Mountain Daylight Time. Sorry, no photos of the eclipse. I missed the last Lunar eclipse trying to take photos. But I do have a photo of the weird pattern of shadows during the eclipse. Very circular.
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New Member Introductions / Re: Hello from Parsons, TN
« Last post by Steve on August 21, 2017, 05:26:05 PM »
Welcome aboard, Dave!
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WeatherCat Integration / Re: AWEKAS
« Last post by Steve on August 21, 2017, 05:24:29 PM »
I am only at 686 feet, so there's likely not much difference between the two.

When I set up my station, I entered elevation, and then carefully adjusted the barometric pressure so that it read the average of the two airports within 20 miles of my station. I've checked this over the years and it has still been close to the average, and I usually have 98-100% rating on BP on CWOP.

I am assuming that the local airport's barometric pressure reading is at elevation, because the METAR contains "sea level pressure not available" for one of the airports. The other, Cleveland Hopkins, shows both on its METAR. Converting the listed seal level millibars to in/hg yields only .02" difference than their posted pressure.

So I'm good either way.
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WeatherCat Feature Requests / Re: Include solar radiation in webcam data?
« Last post by Blicj11 on August 21, 2017, 04:45:02 PM »
Alan, I'll be in my nineties, but maybe I'll still be eating moon pies.
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WeatherCat Integration / Re: AWEKAS
« Last post by Blicj11 on August 21, 2017, 04:42:28 PM »
Edouard:
I came up with the same conclusions you did. And I've had my elevation entered in the setup screen on my VP2 for years so I suspect that Davis does that conversion and that is why WeatherCat does not make any further adjustments for that brand.

TechnoMonkey:
Thanks for the reminder that the Cat allows everyone to calibrate their data should the need arise.

Davis Instruments
Just talked to Davis tech support. If you enter your elevation in the Davis setup screen, the pressure is adjusted for altitude and gives you the "altimeter setting" reading. If you do not enter an elevation, the pressure is not adjusted for altitude and gives you the "sea level" reading. According to Davis, both methods are used and you pick the one you want.

I copy this from a 12-year old post on another forum:

First - let's start with what is actually measured at weather stations - atmospheric pressure. As you know, the air pressure descreases rather rapidly with increasing height - so if we were to make a contour plot of station pressures - what we'd really see is a contour map of the terrain - with lower pressures at higher elevations. As you can guess - this isn't very practical for analyzing the surface weather patterns - so a method needed to be created which could remove the effect of the differences in elevation.

Two methods exist for achieving this - first is the altimeter setting, second is reduction to sea level pressure. The latter uses a math equation that requires knowledge of what the mean temperature would be of the air below the station all the way down to sea level elevation - essentially what we think the measured pressure would be if we could dig a hole down to the height of sea level and measure the station pressure there. Bad guesses as to what this temperature profile should look like can results in big errors in this calculation - so in regions of sharp terrain SLP values can still vary markedly and make analysis difficult. The altimeter setting used to be the normal method used before SLP - because temperature readings weren't available 24/7 which were needed to make reasonable guesses for the SLP reduction. So, the altimeter setting has no temperature dependence, but again uses a fancy math formula to try and guess what the air pressure measurement would be if we could move the site down to sea level elevation. It is generally thought that the SLP measurement is a better way to do this adjustment than the altimeter setting method - but not all agree.


What are you doing?
I'm interested in which method my fellow Weather Catters are reporting? Do you adjust for altitude or not?
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