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General Astronomy >> General Observing and Astronomy

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Bill McNeal
sage


Reged: 10/07/07

Clear Sky Charts Accuracy new
      #5992366 - 07/27/13 02:34 AM

CSCs are very helpful and the best observing weather resource I've found,, but are they reliable? Anyone encounter errors or discrepancy in the weather forecast, or are they consistently accurate?

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Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Clear Sky Charts Accuracy new [Re: Bill McNeal]
      #5992373 - 07/27/13 02:42 AM

They are a great at-a-glance starting point for determining whether conditions will be favorable for observing, this is where they shine. The next step for me is to always check AccuWeather, specifically the hourly forecast. AccuWeather also does their own 'Astronomy' forecast which is somewhat useful as well because you can take a look at a week at a time, unlike CSC which is only 2 days (~45 hrs), though it's not that informative overall by itself but it is still helpful I am always looking to plan observing as much in advance as possible.

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frito
Pooh-Bah


Reged: 10/05/12

Loc: Fremont, CA
Re: Clear Sky Charts Accuracy new [Re: Starman81]
      #5992378 - 07/27/13 02:50 AM

in my experince its a good guide, the weather is the weather. i've had great seeing when CSC said i'd have average and vise versa. transparency is somewhat harder to judge. overall I use it to tell me what the general condition forcast should be, if i'm really interested to know what is going on with my local forcast i will turn to convential weather sites as well as raw data feeds from the NOAA GOES sat's they are where the info ultimately comes from and the real time data is there to see

http://www.goes.noaa.gov/


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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Clear Sky Charts Accuracy new [Re: frito]
      #5992459 - 07/27/13 05:06 AM

The CSC is based on the same computer model output used as the foundation for public and aviation forecasts. The latter products do involve forecasters' brains, whereas the CSC is *just* the computer generated prediction.

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Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Clear Sky Charts Accuracy new [Re: Bill McNeal]
      #5992487 - 07/27/13 06:22 AM

Quote:

Anyone encounter errors or discrepancy in the weather forecast, or are they consistently accurate?




Surely you jest! Have you never seen or listened to a weather forecast before? Have you ever found one that is consistently accurate? Can't be done with the current state of technology, and very likely can't be done ever, for theoretical reasons.

The CSC is a fine and useful tool, but often a little wrong and occasionally very wrong, just like every other weather forecast.


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City Kid
Carpal Tunnel
*****

Reged: 05/06/09

Loc: Northern Indiana
Re: Clear Sky Charts Accuracy new [Re: Bill McNeal]
      #5992498 - 07/27/13 06:35 AM

I have found them to be fairly accurate most of the time. Like others have said, we're talking about the weather here so it's impossible to be 100% accurate but they do a pretty good job. It seems that high, thin clouds are more often than not the source of inaccuracies when it's not as transparent as the CSC predicts.

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Cotts
Just Wondering
*****

Reged: 10/10/05

Loc: Toronto, Ontario
Re: Clear Sky Charts Accuracy new [Re: City Kid]
      #5992703 - 07/27/13 10:15 AM

I like CSC very much.

I also am a fan of Skippy sky which has a nice feature: it distinguishes between low, middle and high cloud.

If you live in the LakeErie, Lake Ontario region this site is fabulous. It has all the radars, satellites etc. that you could ask for.

It's all still a bit of a coin-toss though....

Dave


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Seldom
scholastic sledgehammer


Reged: 08/05/12

Loc: N of Cedar City Light Dome
Re: Clear Sky Charts Accuracy new [Re: Cotts]
      #5992739 - 07/27/13 10:38 AM

You really need a bunch of weather sites to compare. I just added Skippy Sky to mine.

http://www.intellicast.com/National/Wind/JetStream.aspx is nice to know. So's this http://weather.gc.ca/astro/imageview/viewImage_e.html?urlpath=/data/prog/regi...

Seems we owe a great debt to Canadian weather forecasters, but what I've been seeing for the past two weeks just makes me depressed.


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BrooksObs
professor emeritus


Reged: 12/08/12

Re: Clear Sky Charts Accuracy new [Re: Seldom]
      #5992799 - 07/27/13 11:14 AM

I would give CSC about a 60% accuracy rate when it calls for clear evening skies for the NE United States.

I cannot comment precisely on elsewhere, but locate situations/terrain in the Northeast seems to strongly skew its prediction accuracy. I would note that CSC seems to me to be more accurate for daytime conditions than evening ones around here.

As somewhat of an amateur meteorologist myself, ANY "predictions" beyond 48 hours these days seems little more than a WAG. Often I can see decided flaws in the official NWS forecasts for my region. Incidentally, I've seen the NWS predict 8 clear nights here over the past two weeks. There were exactly none until last evening!

BrooksObs

Edited by BrooksObs (07/27/13 11:19 AM)


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StrangeDejavu
Carpal Tunnel
*****

Reged: 03/20/13

Loc: Florida
Re: Clear Sky Charts Accuracy new [Re: Bill McNeal]
      #5992822 - 07/27/13 11:26 AM

I have learned that the CSC is a good indicator, but ultimately one needs to rely on their own vision. I've been burned by the CSC twice when I was first starting out.

The first time, the CSC showed 5/5 Cloud Cover, 4/5 Transparency, 5/5 Seeing. My initial reaction of course was: I set up the light shade, bug sprayed up, let my Dob cooldown and that entire night, clouds filled every inch of the sky.

It goes both ways, though. The second time, the CSC showed mostly white blocks, so I didn't even bother going outside to check. It wasn't until I woke up to use the restroom at around 2:00am that I popped outside and saw 5/5 conditions. Distressed that I missed out on all that time, I quickly set up and took advantage of it until sunrise, where I went back to sleep.

It can be accurate some times, but i've learned to check the skies myself each night. You can usually stare at a bright star for 5-10 seconds and observe how bad it's "twinkling". The amount of "twinkle" tells you how steady atmospheric conditions are; little to no twinkle is preferred for DSO. I've yet to learn a good way to gauge Seeing, so I still turn to the CSC for that.


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John_G
sage


Reged: 01/18/10

Re: Clear Sky Charts Accuracy new [Re: StrangeDejavu]
      #5992841 - 07/27/13 11:37 AM

I like it for giving me an idea on which way the clouds are rolling. I find it very reliable most nights.

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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Clear Sky Charts Accuracy new [Re: John_G]
      #5992986 - 07/27/13 01:04 PM

Mitch,
Your description of the way you use the CSC, where you *seem* (?) to rely primarily or exclusively on the time-series hourly blocks, prods me to issue this *important* note to all users:

Click on at least one of those cloud cover blocks to see a forecast map of your whole part of the country.

The time series blocks represent merely a *single pixel* taken from that image. You must see the bigger picture. Do this on a few occasions and you'll soon enough see why.

And by the way, those map images can be animated.


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StrangeDejavu
Carpal Tunnel
*****

Reged: 03/20/13

Loc: Florida
Re: Clear Sky Charts Accuracy new [Re: GlennLeDrew]
      #5993005 - 07/27/13 01:14 PM

Quote:

Click on at least one of those cloud cover blocks to see a forecast map of your whole part of the country.






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WarmWeatherGuy
Carpal Tunnel
*****

Reged: 08/27/11

Loc: Orlando, FL 28° N, 81° W
Re: Clear Sky Charts Accuracy new [Re: Bill McNeal]
      #5993010 - 07/27/13 01:19 PM

Quote:

CSCs are very helpful and the best observing weather resource I've found,, but are they reliable? Anyone encounter errors or discrepancy in the weather forecast, or are they consistently accurate?




If you're referring to ClearDarkSky.com then here is what I've found here in Florida. Whatever the predicted humidity the actual humidity will be 100%. If it says the humidity will be 60% then expect dew (always expect dew).

If you click on a little square you will see a map for that time. The map will show a contour of different levels of whatever the square was (cloud cover, seeing, etc.) and a big plus sign showing your location. If you are on the edge of a contour then the prediction is less likely to be accurate. If your plus sign is in the center of a region all the same color then the prediction is more likely to be right.

Also, you can animate the map or single step forwards and backwards in time. Usually the first part of the animation has already happened. You are seeing a prediction of what has already happened. That prediction was made before it happened though and if it is way off from what eventually happened then the rest is less likely to be accurate.


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Ed Wiley
scholastic sledgehammer


Reged: 05/18/05

Loc: Kansas, USA
Re: Clear Sky Charts Accuracy new [Re: StrangeDejavu]
      #5993012 - 07/27/13 01:20 PM

2+ on Skippy Sky!

Ed


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REC
Post Laureate
*****

Reged: 10/20/10

Loc: NC
Re: Clear Sky Charts Accuracy new [Re: Cotts]
      #5993102 - 07/27/13 02:10 PM

David, thanks for the tip....just added it to use along with CSC

Bob


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GeneT
Ely Kid
*****

Reged: 11/07/08

Loc: South Texas
Re: Clear Sky Charts Accuracy new [Re: Bill McNeal]
      #5993235 - 07/27/13 04:09 PM

I find them very helpful, but often wrong. Last week, I had just received four new eyepieces. The Clear Sky Charts indicated that viewing would be good in San Antonio. I headed out to my pretty good dark sky site and set up. At sunset, the clouds and haze began to clear. I was getting ramped up. Then, 30 minutes after sunset, the clouds slowly thickened. An hour after sunset, the only thing I could see was Arcturus, through a sucker hole. I tested out the eyepieces to ensure no defects, and that there would be plenty of infocus on one of them.

Any other evening, I would have been really upset because the predictors all said the the evening skies would be clear, to include Clear Sky Charts. However, the evening was not a waste because I was able to give my new eyepieces a check ride.


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JayinUT
I'm not Sleepy
*****

Reged: 09/19/08

Loc: Utah
Re: Clear Sky Charts Accuracy new [Re: GeneT]
      #5993374 - 07/27/13 05:57 PM

Clear Sky is just one of several sites I use. I feel strong if your going to be a serious visual observer you have to become an amateur weather forecaster for the sites you use. Time/experience/knowing how to use some websites helps one to know if a site is good to use or not. Here are the sites.
1 SkippySky Astronomy

2. NWS Activity Planner I enter my data that I want to capture with the latitude and longitude of my site's location and I get this information, link. This information is about 90% accurate.

3. Intellicast provides a quick look at info for that day and a few days ahead. Matches with 2 above for me.

4. Next Gen Weather Lab. I like this site because I can click on region on the left side, go to my region and select visible for that satellite image, vapor which for me is critical to know.

6. NWS Mesonet Reports. This is critical in making a determination of how a site is looking. I pick a site near to my observing site and can read wind, direction, temp., relative humidity and dew point, It helps me to know what to wear, will I need dew protection, do I camp over or come home etc., as I look at the current and historical data by examining the site and clicking on it etc.

7. wunderground.com is a forecast site that is relatively accurate.

Edited by JayinUT (07/27/13 05:58 PM)


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herrointment
Post Laureate
*****

Reged: 03/12/11

Loc: North of Hwy. 64
Re: Clear Sky Charts Accuracy new [Re: GeneT]
      #5993379 - 07/27/13 05:57 PM

I have always felt that the accuracy of the CSC was dependent on the users knowledge of current weather beyond what is presented in the chart and the users ability to interpret the data that is in the CSC.

It's a great personalized product and Mr. Danko offers it to you at no charge. I would hate to be without it.


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star drop
contra contrail
*****

Reged: 02/02/08

Loc: Snow Plop, WNY
Re: Clear Sky Charts Accuracy [Re: herrointment]
      #5993955 - 07/28/13 12:23 AM

None of the forecast models really work in my area. The Clear Sky Chart gives me a heads up that the sky might be clear. The seeing is guaranteed to always be worse than predicted. Then it drops back to past experience and hourly checking by eye.

Example: In the winter the Doppler radar in Buffalo sees a few flurries thirty miles out in my direction. At my location twenty miles further out it might be clear, flurries or three inches of snow per hour for hours on end.


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