Problems contouring sparse array

Hello,

I am having issues contouring an array of snowfall accumulation data that is generally sparse and also contains very small values. I manipulated WRF output files to end up with 6-hourly accumulated snowfall ("SNOW_6HR") over a 100 x 100 grid. "okay.nc" contains one time period where the plot is okay. "bad.nc" contains a different time period where I get the error messages:

warning:ContourPlotInitialize: scalar field is constant; ContourPlot not possible:[errno=1102]
warning:ContourPlotSetValues: Data values out of range of levels set by EXPLICITLEVELS mode

I looked at "bad.nc" with ncview, and also dumped out values using "ncl_filedump -v SNOW_6HR bad.nc", and in both cases non-zero data showed up. I have similar output every 6 hours over this entire month, and "bad.nc" represents the only time this month where this problem occurred. It has the sparsest grid (least amount of non-zero values) of the entire month. Note that I also tried setting cnLevelSelectionMode to "AutomaticLevels", and still got the first error message. I also tried converting the array to double precision, which did not help either. There are some very small values in there (down to 10^-41), but when I manipulated the data array in NCL to set all zero values to some multiple of one of the array indices (and left the extremely small values alone), it plotted with no errors. So this has me thinking that the large expanses of zeros across the domain might be an issue.

If anyone can help me with this I would appreciate it. Thank you!

Daniel Steinhoff
Polar Meteorology Group
Byrd Polar Research Center
The Ohio State University

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