NUCAPS 850mb Theta-E: A rough comparison to SREF and RAP13 850mb Theta-E

There's isn't really a good "real data" comparison one can make for 850mb Theta-E values (at least, not that I know of). It would be easier to make the comparison at the surface, but I don't believe NUCAPS allows this (it doesn't really do too well in the boundary layer). So...I did a rough comparison of NUCAPS 850mb Theta-E (top left) to both the SREF 850mb Theta-E (top right) and RAP13 850mb Theta-E (bottom left). I say "rough" because with the pass occurring just after 19Z, that's when the NUCAPS data are valid, but the SREF data are valid for 18Z and the RAP13 data are valid at 20Z.

There is, naturally, some disagreement within the model data regarding 850mb Theta-E values, so the NUCAPS data don't match up "perfectly" with either model in many locations around the country. (The amount of cloud cover and the reliance on microwave retrieval may also be playing significant roles, since there were a lot of "yellow" sounding dots.) Still, there are areas where it is close, especially where the values are lower in non-/fewer-cloud areas, such as across N MN, E WI, MI, and down into E IL, IN and OH. (Perhaps somewhat due to a dry bias, per the developer.)

As Theta-E numbers get higher, there will obviously be more moisture in the atmosphere, so the satellite signal is probably being scattered, etc. a bit more, leading to some skewing to the numbers. Areas where clouds are abundant and/or thick are actually pretty easy to discern as they show up as some anomalously low Theta-E values, such as what is observed in NE MT, NW ND and cntrl MN. Other areas where there are cu fields or where there is patchy cloud cover (such as across NE), are not so easy to discern within the Theta-E values.

At this point, my recommendation for the NUCAPS 850mb Theta-E product is: "Use with extreme caution" as more testing needs to be accomplished on this product.

- Thomas Bell