II. Problems With the TWC Soundings on 23 June 2008

Problems with the data from the RRS sondes are again starting to impact the analysis of the soundings taken at TWC and the forecasting of convection here in southeastern Arizona.

The FSL time series comparison of GPS IPW versus TWC IPW since the 19th of June indicates that 5 soundings were apparently too dry, while one sounding (1200 UTC 19 June) was very wet relative to GPS IPW. See Figure 1. Careful monitoring of the remotely sensed IPW continues to be the best way to make an initial assessment of how accurate a given TWC sounding might be.

The 00Z sounding last evening (see Figure 2) indicated a deep, well-mixed boundary layer extending up to 500 mb; however, the moisture structure was quite questionable, with very dry conditions off the surface and no recovery to a well-mixed value. This led to the "dry" sounding wrt IPW.

The 12Z sounding this morning (see Figure 3) indicates a very deep residual boundary layer, but the moisture structure is extremely erratic. The IPW values correspond well. Given the unrealistic physical nature of the Td data, I suspect that the agreement of the two IPW values is essentially a coincidence this morning. If the afternoon BL mixes toward 5 g/kg, then there is a small amount of CAPE present; however, if it mixes toward 4 g/kg then there is no CAPE present. Given the erratic Td data trace it is very hard to make a subjective forecast of the late afternoon sounding.