Mixing Height and cloud convection in the Canadian prairies

The Mixing Height (MH), Convective Condensation Level (CCL), and Convective Available Potential Energy (CAPE) are computed with different methods and we examined whether these parameters can help to discriminate between weak and strong convection. The observational data set contains soundings released from Stony Plain in Alberta and The Pas in Manitoba for the summers of 2006 and 2007. The major findings were: (1) The Mixing Height values computed with the Heffter method were reliable provided the critical inversion criterion was adjusted for Prairie conditions. (2) The Mixing Height values computed with the Moist Mixed layer method were in good agreement with Mixing Heights computed with the Heffter method. (3) The Mixing Height values computed with the Holzworth parcel method were less useful in that often the potential temperature did not decrease with height above the ground. (4) Observed convective cloud base heights tended to be lower than the CCL computed using the surface parcel method, the 50 mb mixed parcel method, and the moist mixed parcel method. (5) The MH, the sounding-based CCL, and the CAPE did not differentiate between weak and strong convection. (6) We derived a new parameter: the difference between the convective cloud base and the Moist Air Mixing Height. This parameter did discriminate between the likely occurrence of strong and weak convection.