Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

General Astronomy >> General Observing and Astronomy

Pages: 1 | 2 | (show all)
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Clear Sky Charts Accuracy new [Re: GeneT]
      #5994201 - 07/28/13 06:40 AM

Quote:

I find them very helpful, but often wrong.




Yep, that's it in a nutshell.

Quote:

Last week, I had just received four new eyepieces. The Clear Sky Charts indicated that viewing would be good in San Antonio.




Well, that's a special case. A human forecaster, knowing that you had just bought new equipment, would have forecast clouds regardless of what the weather models said. But you can hardly expect that from a computer . . .


Post Extras: Print Post   Remind Me!   Notify Moderator  
sg6
professor emeritus


Reged: 02/14/10

Loc: Norfolk, UK.
Re: Clear Sky Charts Accuracy new [Re: Tony Flanders]
      #5994238 - 07/28/13 07:49 AM

A useful guide.
They are not produced for the spot that you will be observing from. Not sure of the US but that is usually not comprehended here in the UK.

What is clear? Listening to a program a few weeks back and one of the weather presenters or the the Met Office happened to drop the comment that less then 1mm of rainfall was not considerded as rain. So it can be cloudy, "rain" and you can get wet, but if less then 1mm fell then it wasn't rain and so I suspect you didn't get wet.

Does Clear mean a particular time? If it is not clear at say 10:00pm and you go to sleep, but is clears at say 02:00 then was it a clear night?

What to a Met Office is "clear"? I can often see stars but only the brighter ones. Does high thin cloud/moisture that acts as a slight veil not lumpy cloud rate as clear?

I am still amazed by the number of people that simply do not look outside themselves. I have read many complaints of: "The forecast said cloud, then when I looked out before bed it was clear and I missed an evenings viewing." are many and numerous.


Post Extras: Print Post   Remind Me!   Notify Moderator  
BrooksObs
professor emeritus


Reged: 12/08/12

Re: Clear Sky Charts Accuracy new [Re: sg6]
      #5994283 - 07/28/13 08:36 AM

If one wishes to talk about forecasters' misuse of terminology these days, I can offer an interesting situation that speaks to their growing uncertainty about what is going on.

It used to be that if a clear night was predicted, the forecast would distinctly employ the term "Clear". Now, almost without exception, I see this has been replaced by "Mostly Clear", or "Generally Clear", even when clear skies can unquestionably be anticipated. It's kinda hedging your bets, I suppose.

Likewise, I find only one TV channel (a very local one) that is willing to acknowledge that the presence of considerable cirrus renders the sky no longer "Clear". The other all seem to disregard the fact. I've also seen the major forecasting channels report local conditions as clear even though the entire sky is already solid with cirrus and there is no possibility of change in many hours to come.

I have a good friend who is an on-camera professional meteorologist and we do have some very interesting exchanges sometimes!

BrooksObs

Edited by BrooksObs (07/28/13 10:48 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Clear Sky Charts Accuracy new [Re: BrooksObs]
      #5994988 - 07/28/13 03:44 PM

There is a distinction between forecasts for the aviation community and the public. In the latter case, thin cirrus cloud, through which stars can be seen, is treated as clear.

But the computer models upon which the CSC is based does consider cirrus. And forecasters are very tuned into all cloud types and coverage. Just be aware of the simplifications made in the public forecast.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Madratter
Postmaster


Reged: 01/14/13

Re: Clear Sky Charts Accuracy new [Re: GlennLeDrew]
      #5995277 - 07/28/13 06:28 PM

I find them very useful. BUT, you have to remember that weather predictions are based on a very course grid of input data. There aren't weather stations every mile, etc.

Weather is also a chaotic system meaning that small changes in inputs make for significant changes in the outputs. That is exacerbated by the first problem, but even with very fine grids would still be problematic.

Don't forget a computer actually has to be able to finish the forecast in a useful amount of time as well. So even if we had perfect input information, you couldn't use it.

On top of that, from a global point of view a miss on where the cloud line is going to be by 5 miles is a very accurate forecast. But if you happen to be near the line, as I was the other night, the forecast can be completely wrong for you.

We aren't stirring livers anymore, but the tendency is to have rather unrealistic expectations about weather predictions.

I can tell you that aviation forecasts even 2 hours out are imperfect enough to have operational impacts.

This stuff is REAL hard to get completely right.

EDIT: Just to relate something else, THE hardest course I took in college was physical oceanography. It was dealing with things like the physics of ocean currents, etc. The physics of weather is very similar.

The guys that build these models are very very smart and I have a great deal of respect for them.

Edited by Madratter (07/28/13 06:32 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
brianb11213
Postmaster
*****

Reged: 02/25/09

Loc: 55.215N 6.554W
Re: Clear Sky Charts Accuracy new [Re: Madratter]
      #5995311 - 07/28/13 06:58 PM

Quote:

I find them very useful. BUT, you have to remember that weather predictions are based on a very course grid of input data.



More to the point, the weather forecasts supplied for public use are for locations which may be some considerable distance from your actual location, and take no account of microclimate variations due to local topography. If you learn to listen to the forecasts for the surrounding areas as well as your own, taking account of the local weather patterns you observe over a few years experience, you can do a lot better than the forecasters.

The atmosphere is chaotic enough that however complete and accurate the measurements fed into the predication are, however fine the grid and however much computer power is thown at the prediction, the accuracy is going to fall off as the prediction length increases. Actually for gross weather events like frontal precipitation the forecasts have got quite good, even the 5 day forecasts are now about as good as the 24 hour forecasts used to be 40 years ago ... but whilst showery airstreams may be accurately predicted, predictions of the exact position, timing and intensity of the showers are still very poor indeed - the best bet is to extrapolate from a short series of recent infra-red satellite and rainfall radar images ... that should get you an hour or two's notice of clear patches and/or significant showers heading your way.

Seeing forecasts: in my experience totally useless, apart from the jet stream forecast: it's simply not possible for any forecast to take into account all the small scale influences that affect local seeing.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Astrodj
professor emeritus
*****

Reged: 08/24/11

Loc: Missouri
Re: Clear Sky Charts Accuracy new [Re: herrointment]
      #5995846 - 07/29/13 01:00 AM

Quote:

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.




+1.

In addition to my lifelong love of Astronomy, I am a 2nd generation air traffic controller so being able to accurately determine the weather conditions for anywhere from several hours or less into the future is a major part of my life. My dear old dad, 1st gen ATC, taught me more about interpreting available weather data than most so called meteorologist's know (some are very knowledgeable but many more seem to be nit-wits).

I "out-forecast" the forecasters all the time just like dad use to. He had a saying, "I think it's time they amend the forecast to reflect the current conditions", which if you watch closely, they actually do all the time.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Madratter
Postmaster


Reged: 01/14/13

Re: Clear Sky Charts Accuracy new [Re: Astrodj]
      #5996295 - 07/29/13 10:42 AM

Local knowledge can certainly be a huge advantage in interpreting the forecast. In my area, snow forecast to come in from the West tends to fizzle out. However, snow forecast to come from a storm from the South is much more likely to be the real deal.

Post Extras: Print Post   Remind Me!   Notify Moderator  
REC
Post Laureate
*****

Reged: 10/20/10

Loc: NC
Re: Clear Sky Charts Accuracy new [Re: Madratter]
      #5996946 - 07/29/13 04:33 PM

Well I just checked mine here in NC and got a 3/5 for transparent, but a 4/5 on seeing which we rarely get, so watch out Saturn! Hope it's accurate?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Clear Sky Charts Accuracy new [Re: star drop]
      #5998657 - 07/30/13 03:31 PM

Great info on clicking on the hourly squares. I'm gonna try that for sure.

David


Post Extras: Print Post   Remind Me!   Notify Moderator  
ev2
member


Reged: 07/01/13

Loc: Light Polluted Sunnyvale, CA
Re: Clear Sky Charts Accuracy new [Re: Bill McNeal]
      #5998686 - 07/30/13 03:47 PM

My own experience with them is that they are grossly inaccurate - at least for my specific observing location(s). The nearest chart available to me is for San Jose, CA, but I live in Sunnyvale - several miles to the northwest and closer to the SF bay. So it's not really the fault of the clearsky chart, it's just that where I live, the weather can vary substantially over just a few miles. Those of us closer to the bay have to deal with fog (which has been a curse all week).

I check the clearsky chart once in a while, but generally prefer http://www.wunderground.com/ to really see what's going on and what to expect.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Clear Sky Charts Accuracy new [Re: ev2]
      #5999603 - 07/31/13 06:55 AM

Quote:

My own experience with them is that they are grossly inaccurate - at least for my specific observing location(s). The nearest chart available to me is for San Jose, CA, but I live in Sunnyvale - several miles to the northwest and closer to the SF bay.




Right, the San Francisco Bay Area surely has the most intensely local weather of any densely populated place in the continental U.S. A quarter mile can often cause a 10F shift in temperature and a change from totally clear skies to complete cloud cover.


Post Extras: Print Post   Remind Me!   Notify Moderator  
derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Clear Sky Charts Accuracy new [Re: Tony Flanders]
      #6000387 - 07/31/13 06:19 PM

I wish sites like cleardarksky and 7timer would put up information about how accurate the forecast has been in the past. One problem is they can't get complete feedback. For instance, cleardarksky "transparency" is based solely on atmospheric moisture. The forecaster has only limited information on what the transparency actually was.

It's unreasonable to expect perfection from these services. SkippySky has a good statement on not expecting too much, and why.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Feidb
Carpal Tunnel


Reged: 10/09/09

Loc: Nevada
Re: Clear Sky Charts Accuracy new [Re: derangedhermit]
      #6001239 - 08/01/13 10:03 AM

What is it they say about the Pirate Code? Guidelines? Aaarrrgh. That's how I look at it. At least here in Las Vegas, the Clear Sky Clock is usually pretty close, but they get it wrong about as often as every other weather prediction. However, sometimes, they can be a bit more accurte than the local forecast, especially when it comes to a specific spot rather than a general area. I use it all the time. Once in a while, I'll click on the detail to expand say wind, or cloud cover to see the overal map of that specific forecast, then put it in motion to see if my observing spot is on the cusp of something. That may give me a better idea if I'm going to have trouble. Then again, if I haven't been out in a long time, I just go outside, look up, stick my finger in the air, look at my palm trees...

Post Extras: Print Post   Remind Me!   Notify Moderator  
Bill Weir
Carpal Tunnel
*****

Reged: 06/01/04

Loc: Metchosin (Victoria), Canada
Re: Clear Sky Charts Accuracy new [Re: Tony Flanders]
      #6002421 - 08/02/13 12:40 AM

Quote:

Quote:

My own experience with them is that they are grossly inaccurate - at least for my specific observing location(s). The nearest chart available to me is for San Jose, CA, but I live in Sunnyvale - several miles to the northwest and closer to the SF bay.




Right, the San Francisco Bay Area surely has the most intensely local weather of any densely populated place in the continental U.S. A quarter mile can often cause a 10F shift in temperature and a change from totally clear skies to complete cloud cover.




Right. This is exactly what I experience living on the southern tip of Vancouver Island. While I find the CSC for the observatory I use (which you can have one made for your location, just email the site) reasonably accurate it is that precise micro climate thing that can make going further afield a bit of a gamble. For that part just before it gets dark I log into a local surfer website where there are a whole bunch of cameras located around the island. That way it's like sticking my head out the window for a look but now I have a really loooong neck. A 45 minute drive to a "Black zone" with fog is not as good as a 5 minute drive to "Green" with clear.

Bill


Post Extras: Print Post   Remind Me!   Notify Moderator  
derangedhermit
Pooh-Bah


Reged: 10/07/09

Loc: USA
Re: Clear Sky Charts Accuracy new [Re: Bill Weir]
      #6002552 - 08/02/13 03:22 AM

Quote:

This is exactly what I experience living on the southern tip of Vancouver Island. [...]

Bill




What a great place to live! My wife and I spent a week in and around Victoria on vacation and fell in love with the place. Best Vacation Ever!

Lee


Post Extras: Print Post   Remind Me!   Notify Moderator  
JoeR
Pooh-Bah
*****

Reged: 03/07/10

Loc: Columbus, OH
Re: Clear Sky Charts Accuracy new [Re: Widespread]
      #6005681 - 08/04/13 12:55 AM

Mine is solid blue right now and yet it's totally cloudy outside. The CSC is useless around here always inaccurate.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Silver Bear
member


Reged: 04/02/13

Loc: Brazos Valley in Texas
Re: Clear Sky Charts Accuracy new [Re: JoeR]
      #6009229 - 08/06/13 11:33 AM

Our local CSC is about the most accurate of our local weather predicters.

Of course, in Texas in the summer, a weatherman can be right all season long by simply saying "Mostly clear, high in the 90's/100's, with a 10-20% chance of a thunderstorm"...except this summer, where we've far more high cloudiness at night in the summer skies than I've seen in over 15 years. The CSC seems to pick up on that pretty good.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | (show all)


Extra information
6 registered and 11 anonymous users are browsing this forum.

Moderator:  cildarith, panhard, tecmage 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 1589

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics