<p>The website <a href="https://www.ventusky.com/?p=20.31;-155.35;6&amp;l=clouds" rel="nofollow noreferrer">ventusky.com</a> offers three models to produce cloud estimate: <a href="https://www.mpimet.mpg.de/en/science/models/icon/" rel="nofollow noreferrer">ICON</a>, <a href="http://www.nco.ncep.noaa.gov/pmb/products/gfs/" rel="nofollow noreferrer">GFS</a> and <a href="https://en.wikipedia.org/wiki/Global_Environmental_Multiscale_Model" rel="nofollow noreferrer">GEM</a>. They extract a fractional cloud number, shown in percentage.</p>

<p>From the <a href="http://coastwatch.pfeg.noaa.gov/erddap/griddap/NCEP_Global_Best.html" rel="nofollow noreferrer">ERDDAP portal</a> to the GFS model (NCEP_Global_Best), the only relevant data regarding clouds is:</p>

<ul>
<li>dlwrfsfc (net downward longwave radiation flux, $Wm^{-2}$) </li>
<li>dswrfsfc (net downward shortwave radiation flux, $Wm^{-2}$) </li>
</ul>

<p>Is there a way to estimate fractional cloud coverage from these two parameters or does GFS offer some other product for global cloud coverage?</p>

<p>Is there a GRIB or other type of portal with an API to access cloud coverage estimates?</p>

<hr>

<p>Edit:  I tried openDap as suggested, but the help pages are not clear.  And I don't understand the ranges on the time specifications. Let's say I want to look at 22N, 155W (just 1 point) and look at a 24-hour time frame. I tried <a href="https://rda.ucar.edu/thredds/dodsC/aggregations/g/ds084.1/1/ds084.1-2017/TwoD?lat[88:1:88],lon[820:1:820],time[301950:1:301970],Total_cloud_cover_entire_atmosphere_Mixed_intervals_Average[0:1:0][0:1:0][0:1:0]" rel="nofollow noreferrer">this</a>.</p>

<p>Lat 88, lon 820, time 301950-301970 (I just assumed, probably incorrectly that it ends at the current offset from  2015-01-15T00:00:00Z).  But the results are not what I would expect.  </p>

<p>Any help would be appreciated.</p>

CC BY-SA 3.0
2017-04-08T08:19:25.587Z
@gansub that something is on topic elsewhere on the internet does not make it off topic here.
Semidiurnal Simon
CC BY-SA 3.0
2017-04-08T11:46:28.583Z
@gansub that something is on topic elsewhere in Stackexchange does not make it off topic here ;-)

More seriously, I would argue that while providing detailed support on OpenDAP in a way that was not earth science specific would be off-topic here, simply suggesting that OpenDAP might be a solution to an earth science problem is not.
Semidiurnal Simon
CC BY-SA 3.0
2017-04-08T19:46:00.953Z
@gansub This forum seemed a little slow, so I thought it would be ok to discuss the mechanics of how to access the data which was part of my original question.  While OpenData might help with the technical bits I think there are weather specific questions about what OPeNDAP settings and results are.
user6972
CC BY-SA 3.0
2017-04-08T23:22:58.023Z
@gansub ah, apologies - I hadn't spotted the sequence of edits. I still probably wouldn't complain about off-topicness in this case, but I'm not any sort of authority :-)
Semidiurnal Simon
<meteorology><measurements><clouds><open-data>
How are global cloud cover estimates generated and how is the data accessed?
user6972
# How are global cloud cover estimates generated and how is the data accessed?

(Asked by: username_0 on 2017-04-07)

The website [ventusky.com](https://www.ventusky.com/?p=20.31;-155.35;6&l=clouds) offers three models to produce cloud estimate: [ICON](https://www.mpimet.mpg.de/en/science/models/icon/), [GFS](http://www.nco.ncep.noaa.gov/pmb/products/gfs/) and [GEM](https://en.wikipedia.org/wiki/Global_Environmental_Multiscale_Model). They extract a fractional cloud number, shown in percentage.

From the [ERDDAP portal](http://coastwatch.pfeg.noaa.gov/erddap/griddap/NCEP_Global_Best.html) to the GFS model (NCEP\_Global\_Best), the only relevant data regarding clouds is:

* dlwrfsfc (net downward longwave radiation flux, $Wm^{-2}$)
* dswrfsfc (net downward shortwave radiation flux, $Wm^{-2}$)

Is there a way to estimate fractional cloud coverage from these two parameters or does GFS offer some other product for global cloud coverage?

Is there a GRIB or other type of portal with an API to access cloud coverage estimates?

---

Edit: I tried openDap as suggested, but the help pages are not clear. And I don't understand the ranges on the time specifications. Let's say I want to look at 22N, 155W (just 1 point) and look at a 24-hour time frame. I tried [this](https://rda.ucar.edu/thredds/dodsC/aggregations/g/ds084.1/1/ds084.1-2017/TwoD?lat[88:1:88],lon[820:1:820],time[301950:1:301970],Total_cloud_cover_entire_atmosphere_Mixed_intervals_Average[0:1:0][0:1:0][0:1:0]).

Lat 88, lon 820, time 301950-301970 (I just assumed, probably incorrectly that it ends at the current offset from 2015-01-15T00:00:00Z). But the results are not what I would expect.

Any help would be appreciated.

**Tags:** meteorology, measurements, clouds, open-data

> **Comments:**
> **username_1**: @gansub that something is on topic elsewhere on the internet does not make it off topic here.  
> **username_1**: @gansub that something is on topic elsewhere in Stackexchange does not make it off topic here ;-)  More seriously, I would argue that while providing detailed support on OpenDAP in a way that was not earth science specific would be off-topic here, simply suggesting that OpenDAP might be a solution to an earth science problem is not.  
> **username_0**: @gansub This forum seemed a little slow, so I thought it would be ok to discuss the mechanics of how to access the data which was part of my original question.  While OpenData might help with the technical bits I think there are weather specific questions about what OPeNDAP settings and results are.  
> **username_1**: @gansub ah, apologies - I hadn't spotted the sequence of edits. I still probably wouldn't complain about off-topicness in this case, but I'm not any sort of authority :-)  

---

## 0 answers

