Shown above are the GPS precipitable water estimates for the TWC (Tucson) sounding site for the past five days. Note that there is a slight dry bias for the morning soundings during this period, but the afternoon RRS sonde data dry bias is very large. My contention is that these are unacceptably inaccurate data for use in short-term forecasting (often the most critical public forecasts that the NWS makes).
On the evenings of August 4, and again on the 5th (00Z on the 5th and 6th), strong storms were approaching the Tucson metro area from higher terrain. The observed and transmitted soundings for TWC have absolutely no CAPE available for storms. This is because of the extreme dryness indicated by the RRS sondes in the deep boundary layers. The sounding on the 6th appears to have "missed" 5/10s to 6/10s of an inch of the actual precipitable water present.
My second contention is that there is no way that a forecaster can quickly guess what the actual sounding structure might be - this is of course a game with infinite solutions. Strong storms, gusty winds and restricted visibilities due to blowing dust occurred on both evenings. Who knows how some future researcher might interpret the archived, official, RRS upper-air data with the observed weather?
The bad data, of all types, in the RRS soundings constitute a serious problem that no one in NWS management seems to want to talk about, much less formally warn the external user community.
Personal note - I'll be out of town witout computer access tomorrow.
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