UNR - Mesoscale Discussion

1930Z: Quite the difference in moisture across the UNR CWA with dewpoints in the mid-60s across central & northern SD, mid to upper 50s across western SD, & only in the 40s across NE WY & the Black Hills. The all-sky LAP CAPE mirrors this moisture distribution with CAPE values from 700-1000 J/kg across the northern part of the UNR CWA, & well under 500 J/kg across the rest of the area. Spatially, all-sky CAPE matches up well with the MLCAPE on SPC mesoanalysis but is a few 100s J/kg lower, all in all they compare quite well. MLCAPE values are not forecast to increase much, maybe up to 1000 J/kg across SW SD & 1500 J/kg across the northern CWA.
All-sky CAPE at 19Z:

While CAPE looks meager shear may be able to make up for it with 40-45 kts of effective bulk shear expected to be in place by late afternoon.
No real noticeable forcing mechanisms are evident via a surface analysis with the main show expected to be with storms forming over the mountains in SE WY & moving into the southern CWA. However I'm able to pick out what appears to be a dry intrusion on the all-sky sfc-900 mb PW product across SW SD. Along with the storms moving in from WY the HRRR initiates a supercell south of the Black Hills this evening right where this feature is located so it'll be interesting to see if the all-sky products are picking up on a subtle feature not identifiable due to the lack of sfc obs in the area. 
 All-sky SFC-900 mb PW:

Most favorable for severe weather will be the steep mid-level lapse rates with SPC mesoanalysis showing 700-500 mb lapse rate values of 8-8.5 C/km associated with an EML moving into SW SD. Unfortunately the NUCAPS soundings are not available yet so I can't compare them to the mesoanalysis values but will do so as soon as they are available.
All in all I think a general low-end hail & wind threat today is possible with the storms moving in from WY, primarily as a result of the steep lapse rates. If any storms are able to develop with the feature across southern SD I would expect more of a larger hail threat given the likely supercell mode.

Peter Sunday