Paul from Phoenix comments on the post about last evening's TWC sounding that was very dry relative to GPS value: I am sure the NWS forecasters are very aware of the issue with "dry" soundings and can easily account for the discrepancy when analyzing the sounding. Impacts on the short term forecast should be negligible at best.
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I think that the above assessment is a bit optimistic. I have been documenting problem cases on the blog for about three years now and think the problem is fairly serious. Many forecasters (as indicated by things like their forecast discussions) do accept the bad data as being accurate. For example, consider the FD from Tucson NWS early last Sunday morning:
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...KTWC SOUNDING SHOWED A CONSIDERABLE DECREASE IN MOISTURE WITH A PWAT OF 1.15 INCHES [GPS PW was 1.45 inches] COMPARED TO 1.60 INCHES FROM SATURDAY MORNING...AND 1.50 INCHES [GPS PW was 1.80 inches] FROM FRIDAY EVENING. WITH THAT SAID I EXPECT MOST OF THE SHOWERS AND THUNDERSTORMS TO OCCUR MAINLY OVER MY EASTERN ZONES.....
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Blue inserts are my annotations. Clearly this forecaster believed the RRS data to be accurate and factored it into his/her forecast. I feel that my contention that these bad RRS data do impact some NWS forecasts negatively (both subjective and numerical forecasts) is valid.
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