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An additional Seeing forecast product

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#1 Kiwi Paul

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Posted 25 November 2021 - 08:08 PM

Hi all,

 

I was recently having a look around the web site of my old employer (Environment Canada, the umbrella organisation for the Canadian Weather Service) and I found that they produce a number of products for Astronomy.

Amongst others are Seeing and Sky Transparency forecasts. I haven't heard anyone refer to these so I thought I would post a link.

 

Take a look at: https://weather.gc.c...o/index_e.html 

 

It seems to me one way to use these would be to:

1. Take a look through the Cloud cover animation to see what is coming your way for some observation window you have in mind.

2. Then view the Sky Transparency Loop and look in particular at the times of interest (this panel accounts for the total cloud distribution).

3. Have a look at the Seeing loop and in particular your target observation times. You can then evaluate the forecast seeing. The legend is in the notes preceding the Seeing panel but white is Cloudy, grey is very poor Seeing ranging to Dark Blue which indicates Excellent Seeing.

 

Here are some sample panels:

Env Canada Total Cloud Fcst T+12.jpg Env Canada Sky Transparency Fcst T+12.jpg Env Canada Seeing Fcst T+12.jpg

 

For the cloud panel, there is an Eastern Canada image as well. You can probably find a North America wide one on the site.

 

I would be interested to hear how the Seeing and Transparency forecasts perform. (BQ you might be interested in these?)

 

Cheers Paul

 


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#2 gatsbyiv

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Posted 25 November 2021 - 08:43 PM

I believe these are the forecasts that http://www.cleardarksky.com/ is based upon.  In fact, if you click on a specific hour block on cleardarksky, it takes you to the maps above.


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#3 Kiwi Paul

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Posted 25 November 2021 - 09:14 PM

Thanks, I have heard about Clear Dark Sky but didn’t know they used these maps. How to they perform?
Paul

#4 wrvond

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Posted 25 November 2021 - 10:03 PM

Thanks, I have heard about Clear Dark Sky but didn’t know they used these maps. How to they perform?
Paul

I find it very reliable. It has become my preferred forecasting tool.


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#5 Look at the sky 101

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Posted 25 November 2021 - 10:06 PM

Hi all,

 

I was recently having a look around the web site of my old employer (Environment Canada, the umbrella organisation for the Canadian Weather Service) and I found that they produce a number of products for Astronomy.

Amongst others are Seeing and Sky Transparency forecasts. I haven't heard anyone refer to these so I thought I would post a link.

 

Take a look at: https://weather.gc.c...o/index_e.html 

 

It seems to me one way to use these would be to:

1. Take a look through the Cloud cover animation to see what is coming your way for some observation window you have in mind.

2. Then view the Sky Transparency Loop and look in particular at the times of interest (this panel accounts for the total cloud distribution).

3. Have a look at the Seeing loop and in particular your target observation times. You can then evaluate the forecast seeing. The legend is in the notes preceding the Seeing panel but white is Cloudy, grey is very poor Seeing ranging to Dark Blue which indicates Excellent Seeing.

 

Here are some sample panels:

attachicon.gifEnv Canada Total Cloud Fcst T+12.jpgattachicon.gifEnv Canada Sky Transparency Fcst T+12.jpgattachicon.gifEnv Canada Seeing Fcst T+12.jpg

 

For the cloud panel, there is an Eastern Canada image as well. You can probably find a North America wide one on the site.

 

I would be interested to hear how the Seeing and Transparency forecasts perform. (BQ you might be interested in these?)

 

Cheers Paul

I think they're very good .


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#6 Benschop

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Posted 25 November 2021 - 10:10 PM

That is correct. Allan Rahill is the meteorologist behind the forecast data, while Attilla Danko is the Clear Sky Clock owner / programmer who put the data into location specific forecast pages for us.

Both are fellow amateur astronomers and are delivering a great service to our hobby. 

 

I believe these are the forecasts that http://www.cleardarksky.com/ is based upon.  In fact, if you click on a specific hour block on cleardarksky, it takes you to the maps above.


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#7 james7ca

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Posted 26 November 2021 - 01:50 AM

In my location (southern California and near to the coast) these forecasts are completely unreliable. So, YMMV depending upon your location.

 

The only reliable way I've found to forecast cloud cover is to use the realtime Nighttime Microphysics satellite imagery to see what is actually coming my way (in terms of clouds). Here is a link to one source for that service:

 

  https://weather.cod....orbar=undefined

 

-- and here --

  

  https://www.star.nes...ysics&length=12

 

As for the seeing conditions, there is really no way of knowing other than to understand your own weather patterns. For example, many of the clear nights we get here in coastal San Diego county happen under the so-called Santa Ana wind conditions which are virtually guaranteed to produce very poor seeing conditions. Thus, since I know my local weather patterns I can count on having poor seeing whenever there is a Santa Ana. Otherwise, when we have a marine influence the seeing can be pretty good, but the marine layer usually (almost always) brings low clouds at around sundown and most nights are 100% overcast.

 

Thus, I have only a handful of nights each year that are both clear of clouds and with good seeing conditions. To get that kind of night you need the following:

 

1.) No Santa Ana condition.

2.) No marine layer clouds (obviously, but we have clouds on most nights). 

3.) Wait at least 24-hours after the passage of any cold front.

4.) Pray that the marine layer doesn't arrive within the next 30 minutes (it can move amazingly quickly from offshore, in some cases the clouds can precipitate out of a clear sky).


Edited by james7ca, 26 November 2021 - 02:47 AM.

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#8 Kiwi Paul

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Posted 26 November 2021 - 04:06 AM

Thanks for your comments above folks.

 

james7ca, I agree with you whole heartedly about how you need to know your local weather patterns. You explain your situation well.

 

In my case I know that ahead of a frontal band moving up and approaching from the southwest over the South Island, both the low level and upper level winds (the JetStream) will strengthen, and seeing will be very poor. The front goes by and the low level winds switch around to the south (north for you) and gradually ease with the sky clearing. The Jet Stream winds have also backed around to the south west and eased, As the low level winds move further around to the east and northeast (coming over modestly hilly terrain) and drop off to light, I know I have a very good chance of good seeing. But as soon as the low level winds strengthen out of the northwest (flow across some ranges) the seeing will deteriorate whether the Jet Stream winds increase or not. These ideas are rather like your circumstances. If winds are light at all levels under settled anticyclonic conditions, then seeing will likely be very good.

 

But in general, I do keep an eye on Meteoblue for trends in the various elements, especially Jet Stream wind speeds. When the Seeing Indices drop, I know conditions are usually not going to be good especially for Index 2 dropping to 2 or less even while Index 1 is 4. I use Windy.com to look at the low level wind behaviour (usually at 925 hPa).

 

So we need to take a mixed approach.

 

Cheers Paul


Edited by Kiwi Paul, 26 November 2021 - 04:08 AM.


#9 RedLionNJ

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Posted 26 November 2021 - 10:32 AM

Thanks, I have heard about Clear Dark Sky but didn’t know they used these maps. How to they perform?
Paul

Next to useless, in my experience. They may do ok for some parts of North America, but in the NE US they're absolutely unreliable - in both directions.




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