Total precipitable water measurements from GOES sounder derived product imagery

Statistics are compiled comparing calculations of total precipitable water (TPW) as given by GOES sounder derived product imagery (DPI) to that comput ed from radiosonde data for the 12-month period March 1998-February 1999. I n order to investigate the impact of the GOES sounder data, these results a re evaluated against statistics generated from the comparison between the f irst guess fields used by the DPI (essentially Eta Model forecasts) and the radiosonde data. It is found that GOES data produce both positive and nega tive results. Biases in the first guess are reduced for moist atmospheres, but are increased in dry atmospheres. Time tendencies in TPW as measured by the DPI show a higher correlation to radiosonde data than does the first g uess. Two specific examples demonstrating differences between the DPI and E ta Model forecasts are given.