afischer
EF4
A couple of recent aircraft soundings from Jamestown, ND show a deep moist layer only weakly capped by 700 temps of 9.5-10 degrees C. SBCINH calculated off the soundings is 50 j/kg at best... probably fully eroded elsewhere where stronger surface heating has occurred. Looks like the SPC mesoanalysis has a good handle on these fields. I'd shoot for the surface boundary like Brian described above.
