I recently started using the Climate Forecast System Reanalysis (CFSR) 6-hourly products (http://rda.ucar.edu/datasets/ds093.0/), and I noticed many values of relative humidity are negative. Is this an error in the dataset? If not, how should I interpret negative values?

  • $\begingroup$ Have you tried accessing the data through a THREDDS data server: nomads.ncdc.noaa.gov/thredds/dodsC/modeldata/cmd_pgbh/2011/…? That usually provides information about valid ranges $\endgroup$
    – arkaia
    Commented Jan 24, 2015 at 2:27
  • $\begingroup$ @aretxabaleta thanks for the comment - No I have not, is this can FTP server? I typed that address in my browser and it says "Unrecognized request". By "valid ranges", do you mean valid humidity ranges, date ranges or else? But I'll look it up and see what I can find. $\endgroup$
    – user2490
    Commented Jan 24, 2015 at 3:27
  • $\begingroup$ @aretxabaleta is it the link you wanted to give nomads.ncdc.noaa.gov/thredds/dodsC/modeldata/cmd_pgbh/2011/… ? I got an "Unrecognized request" as well with yours. $\endgroup$
    – plannapus
    Commented Jan 24, 2015 at 12:04
  • $\begingroup$ Yes, that is it. Sorry. I just posted the one I use to get the data directly. I tend to use THREDDS and Matlab and the function ncgeodataset (code.google.com/p/nctoolbox/wiki/ncgeodataset) to subsample the netcdf without having to dowload large datasets $\endgroup$
    – arkaia
    Commented Jan 24, 2015 at 15:11
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    $\begingroup$ Can you please post a filled contour plot of global RH, with the range of 0 to 1 (or 0 to 100, if RH is a percentage), at the time when you find negative values? This should show where it is negative (out of range being white). Since RH is a positive definite quantity, I suspect this is an issue of either nonconservative advection scheme or nonconservative convection or microphysics parameterization schemes, although the latter typically employ hard limiters on positive definite quantities to make sure they stay in range. $\endgroup$ Commented Jan 25, 2015 at 23:45

1 Answer 1


I am also getting negative relative humidity from the GFS (Global Forecast System): 36-hour predicted atmosphere dataset (Provider: NOAA/NCEP/EMC, their website: http://www.emc.ncep.noaa.gov/index.php?branch=GFS)

I found this link that answers as to why relative humidity is possible in their dataset:


This might apply to the one you have access too.

Let me know if this helps.


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