Modified NUCAPS Soundings-FSD

Noticed some issues with the modified NUCAPS soundings in the FSD area.  In some of the cases where the odd errors in the soundings.  Not sure what caused them or why they showed up but here are some examples.

First pass of NOAA-20.

Note the odd look of the temperature trace in the mid levels (note the sharp increase in temp just above 700mb).  This was noticed in a number of the neighboring dots.  This error seemed to get better the further away you got from this location.  We were hoping this would improve when the second pass came overhead later at 20Z.  Below is an example of this error from the second pass.

Second pass NOAA-20.

As can be seen from the image above, the second pass still had this error (note the sudden change in the temperature trace at about 600mb).  After looking at the conditions in the area, several questions as to why this was occurring came up.  It appeared the surface temperatures were rather reasonable and the atmospheric conditions were also close to what the sounding may be trying to depict.  There was some thought the modified NUCAPS may be having difficulty with the moisture trace rather than the temperature trace.

It was also noted that when using the “pop up skew-T” function it would not see this error.  It was discovered the reason for this is the “pop up skew-T” function would not see the modified soundings that Nsharp would display.  

Why this was occurring I really could not tell.  One of the PIs indicated the algorithm may not be handling the moisture trace well.  It was also noticed the surface wind fetch was coming from the southwest and that is coming off the sandhills of Nebraska.  This is a very wet area and is perpetually wet.  Is it possible that some localized moisture advection was not accounted for?  Can’t say for sure but mention it here to indicate what could be going one.  


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