Cloud Free Night - User survey & feedback

[sharptrack2 (Kevin)]

Originally Posted by philiphart

What else do you look at apart from 300hPa wind? Does good seeing correlate better with light winds, no wind or strong wind at ground level? This last point can probably vary a lot between sites.

Phil

If tonight has any basis to measure by, winds at 10m is extremely relevant to good seeing.

Last week I took note that the jet stream was westerly and reasonably steady, and tonight, while it is southerly over Sydney, it was again steady and the steadiness seems to be more relevant than the direction, given that the lower level winds last week were also steady, onshore at the time. Tonight the lower level winds are all over the shop, splitting across the Blue mountains and seemingly having a mind of their own all the way up the coast.

There was an evening recently where the lower level winds were calm but the jet stream was influenced by an upper level high and was a bit of a mess over Sydney. The seeing was still reasonable to me but maybe not good enough for photography.

Tonight the views were mediocre at best, disregarding the crescent moon. The late arriving clouds didn't help either...

[skysurfer]

Originally Posted by cfn

But, there are currently no plans to release a CFN app.

Indeed, that is not needed when a website is properly designed (and CFN is). Website-replacing apps are just obsolete clutter-ups of your cellphone.
Is it a problem to get worldwide info ? There are now lots of sites such as Meteoblue which cover worldwide.

[speach (Simon)]

I'm a convert to cfn from skippy

[cfn]

Originally Posted by skysurfer

Indeed, that is not needed when a website is properly designed (and CFN is). Website-replacing apps are just obsolete clutter-ups of your cellphone.
Is it a problem to get worldwide info ? There are now lots of sites such as Meteoblue which cover worldwide.

Most providers use the GFS model which is free. Wider coverage comes down to cost and resources. Contributions to help cover running costs are most welcome to help keep us cost neutral.

[marc4darkskies (Marcus)]

Originally Posted by philiphart

Glad we've got you convinced Marcus

I haven't imaged at long focal lengths so seeing has rarely bothered me and consequently I'm no expert on the topic. Do you notice a good correlation between seeing and other forecast parameters? It's easy to create a seeing index based on high altitude wind speeds but only worth doing if it yields meaningful results. What we don't want to do is create a black box formula which spits out impressive numbers without a good basis.

What else do you look at apart from 300hPa wind? Does good seeing correlate better with light winds, no wind or strong wind at ground level? This last point can probably vary a lot between sites.

Phil

Hi Phil,

I confess I'm no expert on these matters either! I don't really know what parameters contribute to seeing conditions but just recently, as suggested above, I overlaid surface winds with jet-stream maps and that seemed OK. That is, low surface winds plus low jet-stream winds = good seeing (on two nights). I haven't tried this often enough to be sure it's a reasonable measure though but so far so good. I imagine it's not that simple though. EG: I'd guess perhaps convection from warm surface temperatures into a cold sky will throw a spanner in the works even when there is no wind (??). Also, even small amounts of intermittent high level cloud seem to mess up seeing - esp at a FL of 3.1m.

The great news is that so far CFN has produced very reliable short term cloud forecasts. Longer term maps aren't bad but I generally only look at the short term maps anyway so I know whether to bother going out.

[Phil Hart]

Originally Posted by skysurfer

Is it a problem to get worldwide info ? There are now lots of sites such as Meteoblue which cover worldwide.

The unique feature that CFN offers is forecasts based on the BoM ACCESS model. The high resolution version is only available for Australian region so there's not really any point to expanding the service.

Also the BoM data is only available for non-commercial purposes so need to keep the focus on what is realistic with volunteer resources. Better to do one thing well than try to be all things to everyone in my book!

Phil

[Phil Hart]

Originally Posted by sharptrack2

If tonight has any basis to measure by, winds at 10m is extremely relevant to good seeing.

Last week I took note that the jet stream was westerly and reasonably steady, and tonight, while it is southerly over Sydney, it was again steady and the steadiness seems to be more relevant than the direction, given that the lower level winds last week were also steady, onshore at the time. Tonight the lower level winds are all over the shop, splitting across the Blue mountains and seemingly having a mind of their own all the way up the coast.

There was an evening recently where the lower level winds were calm but the jet stream was influenced by an upper level high and was a bit of a mess over Sydney. The seeing was still reasonable to me but maybe not good enough for photography.

Tonight the views were mediocre at best, disregarding the crescent moon. The late arriving clouds didn't help either...

What do you mean by the jetstream being steady? I'm not sure that we can characterise what you mean from model data.

Your comments sound realistic in terms of the complexity of factors involved but also indicate that much is related to the synoptic situation and how it interacts with local factors. Very hard to boil down to a "seeing index" based on model parameters that can be used at all locations.

Phil

[multiweb (Marc)]

Originally Posted by marc4darkskies

... I overlaid surface winds with jet-stream maps and that seemed OK. That is, low surface winds plus low jet-stream winds = good seeing (on two nights). I haven't tried this often enough to be sure it's a reasonable measure though but so far so good. I imagine it's not that simple though.

+1 I used the same technique for the SPSP2016 and it worked beautifully for me too. Seeing is probably depending on a whole lot more factors including local conditions but this overlay does the job to at least give you a good 'maybe' and certainly a strong 'no-no' when both wind vectors are too long.

[sharptrack2 (Kevin)]

Originally Posted by philiphart

What do you mean by the jetstream being steady? I'm not sure that we can characterise what you mean from model data.

Phil

Simplistic term for all in one direction and equal velocity across a large area. No disturbances such as when the jet stream has drifted north and you get the less uniform flow under the curve when it exists. I guess the observation I was trying to illustrate was that as long as the upper level winds are of relatively constant velocity, in one direction, the next major contributor to seeing will most certainly be low level winds, as they would have a higher thermal variation from being close to the ground, and when unstable, would be very similar to thermal disturbances on a hot day. If moving at a relatively constant velocity and direction, the variations might be less apparent. All very subjective, based on recent observations.

I also agree that individual experiences will vary according to the micro-climates that exists. I'm slowly building a perception of which macro weather patterns positively influence my immediate micro-climate in the Gosford area. One day soon I'll actually start capturing daily data locally and correlating it to the larger area forecasts, to be able to make a go/no-go decision about setting up for a evening of observing.

[cfn]

Some very exciting news we'd like to share with our supporters in the upcoming survey in spring 2016 about the launch of myCFN, a totally new user experience on Cloud Free Night packed with new features and extensive customisation.