I made some comparisons between a NUCAPS sounding at 1824z near Charleston, SC and the 12z observed sounding at Charleston, SC. Both soundings were manually modified to a surface temp/dew point of 87/72 (modified NUCAPS soundings were unavailable at this location). Overall the NUCAPS sounding matches the overall profile fairly well with mid-level drying and a fat CAPE profile aloft, with similar SBCAPE, PWATs, and DCAPE values.  I did notice a warm layer centered near 700mb (the base of what appears to be an elevated mixed layer), which resulted in higher MLCIN values and higher 700-500mb lapse rates. This could indicate more capping than is actually present, though perhaps stronger convection where the cap does break. This warm layer also appears warmer than in an 18z HRRR initialized sounding at the same location.

I also looked at Gridded NUCAPS 700mb temperature data compared to 18z 700mb temperatures from the RAP and GFS. While there was some missing data in the area of interest from Gridded NUCAPS, the values just south of that area are higher than what the models were showing.

Late day update: the modified NUCAPS soundings eventually filled in.

It was a few degrees cooler at the surface, but that may be because it went off the 17z RTMA rather than the 18z METARs at that time.

– Barry Allen