Now that's what I call answering the question. Can't get the links to work at present but I'll come back to it later. Interesting stuff. I seems there are 500 of these stations worldwide.
Thanks for taking the time to put this together! I was able to try it out last weekend with some success. It will take some more practice to get used to examining the data.
I don't know. One of the site admins must have attached that image for use on the front page. The primary photo I used is courtesy of Natural. I would assume it is in Brazil.
wtfo, I commend you on putting a lot of effort into this. By reading this article, I can tell you have spent some time studying the weather. However, as a meteorologist myself, I have to make the following comments on the content.
These guidelines you are showing are useful as rough estimates for determining if clouds will be present and at what level. However, I think you should mention that these are rules of thumb and are not strictly based on pure science.
For example: In order for a cloud to be present, the relative humidity MUST reach 100%. You state that a relative humidity of 70% should be used to determine if there is a cloud. This appears to be misleading, as the pure science says this is impossible. In reality, humidity can vary over short distances so that one spot can have 100% and a cloud, while the nearby sounding may have 90% humidity at that level and no cloud. Therefore, your 70% threshold can be used to find the "possibility" of clouds. However, I personally would use a threshold of 80 or 90%. One other thing, 70% humidity usually corresponds to a dewpoint depression of about 10 F (not 5F). I assume this might have been a typo.
Anyway, there are several other "rules of thumb" that you use that would better be explained as such. (e.g., finding out if a cloud is raining.)
First thing to consider here is that this quick lesson is intended for the layman to use, not a meteorologist. My 5F, 70% method is a quick rule generally applicable at all levels of the atmosphere. Of course these numbers change some with temperature, but I was trying to simplify for average folks. Second, I don't know where you got the 100% RH necesssary for cloud formation figure from, but I assure you that the 70% threshold is and has been the accepted threshold (at least in my 20 years as an aviation met and operational met). I believe I proved this in my Quillayute example above. Saying 100% RH is a requirement for clouds is like saying the same for fog formation. And that is totally untrue. If you adopt a 100% RH threshold to locate clouds, you will miss more than you find.
Although Joegrim is right, that you need 100% RH for clouds to form, it depends on other factors as well. For example, in rising air parcels, it's just all too possible that at say, 10,000 foot, such a pocket will be 10C with a RH of 70%, where the surrounding air will have a T of 5C with an RH of 90%. When that parcel will cool off, you'll have nice cumuli forming, because the air gets oversaturated with moisture. In this not too uncommon instance, there are spots where the RH reaches 100%, whereas the surrounding air never gets over 90.
I think this is a good and usable article, because it explains a few guidelines that folks, who don't know shite about the physics of weather systems, are being explained what to look for. In essence, it can prevent people from doing stupid shite.
About Quillayute, i tend to follow this rule: "If it's not raining right now, it will in a wee bit" From September to June, that rule tends to have a higher success rate than any other weather model.
I have been using soundings for operational forecasts for a long time. If I waited for 95% or higher RH to forecast clouds, I would be wrong way more than right. The balloon would have to go right through the cloud to pick up the 100%.
Charles - Jun 9, 2006 12:53 pm - Voted 10/10
thanksI´ll need some time to digest this!
Cheers
Charles
dadndave - Jun 13, 2006 11:37 am - Voted 10/10
CrikeyNow that's what I call answering the question. Can't get the links to work at present but I'll come back to it later. Interesting stuff. I seems there are 500 of these stations worldwide.
mvs - Jun 14, 2006 7:53 am - Voted 10/10
awesome articleGreat tutorial format, thank you!
Fettster - Jun 14, 2006 3:07 pm - Hasn't voted
Thanks!Thanks for taking the time to put this together! I was able to try it out last weekend with some success. It will take some more practice to get used to examining the data.
Thanks again!
montana boy - Jun 16, 2006 4:01 am - Hasn't voted
Nice!This is fantastic information. Thanks!
TempestPeace - Jun 20, 2006 7:21 pm - Hasn't voted
Very interestingThat is very very interesting information..But I must ask Where is that Pic that is displayed on the next to the Article on the Homepage?
wtfo - Jun 22, 2006 5:21 am - Hasn't voted
Re: Very interestingI don't know. One of the site admins must have attached that image for use on the front page. The primary photo I used is courtesy of Natural. I would assume it is in Brazil.
joegrim - Jul 7, 2006 11:21 pm - Voted 6/10
Not quite rightwtfo, I commend you on putting a lot of effort into this. By reading this article, I can tell you have spent some time studying the weather. However, as a meteorologist myself, I have to make the following comments on the content.
These guidelines you are showing are useful as rough estimates for determining if clouds will be present and at what level. However, I think you should mention that these are rules of thumb and are not strictly based on pure science.
For example: In order for a cloud to be present, the relative humidity MUST reach 100%. You state that a relative humidity of 70% should be used to determine if there is a cloud. This appears to be misleading, as the pure science says this is impossible. In reality, humidity can vary over short distances so that one spot can have 100% and a cloud, while the nearby sounding may have 90% humidity at that level and no cloud. Therefore, your 70% threshold can be used to find the "possibility" of clouds. However, I personally would use a threshold of 80 or 90%. One other thing, 70% humidity usually corresponds to a dewpoint depression of about 10 F (not 5F). I assume this might have been a typo.
Anyway, there are several other "rules of thumb" that you use that would better be explained as such. (e.g., finding out if a cloud is raining.)
Thanks for your hard work on this article!
wtfo - Jul 10, 2006 10:21 pm - Hasn't voted
Re: Not quite rightFirst thing to consider here is that this quick lesson is intended for the layman to use, not a meteorologist. My 5F, 70% method is a quick rule generally applicable at all levels of the atmosphere. Of course these numbers change some with temperature, but I was trying to simplify for average folks. Second, I don't know where you got the 100% RH necesssary for cloud formation figure from, but I assure you that the 70% threshold is and has been the accepted threshold (at least in my 20 years as an aviation met and operational met). I believe I proved this in my Quillayute example above. Saying 100% RH is a requirement for clouds is like saying the same for fog formation. And that is totally untrue. If you adopt a 100% RH threshold to locate clouds, you will miss more than you find.
Proterra - Oct 28, 2007 6:25 am - Voted 10/10
Re: Not quite rightAlthough Joegrim is right, that you need 100% RH for clouds to form, it depends on other factors as well. For example, in rising air parcels, it's just all too possible that at say, 10,000 foot, such a pocket will be 10C with a RH of 70%, where the surrounding air will have a T of 5C with an RH of 90%. When that parcel will cool off, you'll have nice cumuli forming, because the air gets oversaturated with moisture. In this not too uncommon instance, there are spots where the RH reaches 100%, whereas the surrounding air never gets over 90.
I think this is a good and usable article, because it explains a few guidelines that folks, who don't know shite about the physics of weather systems, are being explained what to look for. In essence, it can prevent people from doing stupid shite.
About Quillayute, i tend to follow this rule: "If it's not raining right now, it will in a wee bit" From September to June, that rule tends to have a higher success rate than any other weather model.
It wouldn't mind to make that link work, btw.
wtfo - Jul 11, 2006 5:31 pm - Hasn't voted
Re: 100% RH is requiredI have been using soundings for operational forecasts for a long time. If I waited for 95% or higher RH to forecast clouds, I would be wrong way more than right. The balloon would have to go right through the cloud to pick up the 100%.