As a previous blog from today showed the success of the experimental NUCAPS retrieval modification in indicating the cap at LBF, this note points out a limitation of the product.  Because the algorithm always creates low levels that are well-mixed in both temperature and moisture, if the low levels are in fact not well mixed, an error will result.  Today a special 2000 UTC radiosonde launched from Rapid City, SD indicated that the low levels were well mixed in temperature, but not in water vapor:

Compare the experimental NUCAPS retrieval from around 1900 UTC:

This issue will be part of the "next steps" in the experimental NUCAPS project.

You may also notice that the surface values of temperature and mixing ratio differ quite a bit between the two profiles.  Remember, the NUCAPS retrieval is from 1900 UTC and the special radiosonde is from 2000 UTC.  Over that hour the temperature at Rapid City increased from 84 to 92 and the dewpoint decreased from 57 to 52.

Jack Dostalek