More on Issues with GPS and Sounding Precipitable Water

We've posted a few times about discrepancies between precipitable water measured by GPS and National Weather Service Soundings (e.g., How Moist Is It?).  Bob Maddox, former director of the National Severe Storms Lab, discusses how these two measurements compared during summer 2010 in today's post on his Madweather blog.

Given that the differences are sometimes quite large, I wonder how much of an impact the sounding precipitable water, which frequently looks to be too low in the afternoon, impacts numerical forecasts and reanalyses.

And, in case you are wondering, the precipitable water in soundings from KSLC has ben substantially lower than that measured by GPS for the last two days.

Source: NOAA/ESRL