MESOSCALE CONVECTIVE SYSTEMS IN WEAKLY FORCED LARGE-SCALE ENVIRONMENTS .2. GENERATION OF A MESOSCALE INITIAL CONDITION

A series of five mesoscale convective systems (MCSs) developed within a weakly forced large-scale environment on 11 and 12 May 1982. Two of these systems had a large component of motion against the midtroposphe ric how and propagated in a direction nearly opposite to that of the t raveling upper-level disturbances. This description of the evolution o f convection is very different from traditional ones in which convecti on develops and moves more or less in phase with traveling upper-level disturbances. Observations indicate that the initiation and evolution of convection are tied to mesoscale features that are not well observ ed by the conventional observing network, making the structure of the model initial condition a potentially crucial factor in the success or failure of any subsequent numerical simulation. It is found that the initial conditions created using the conventional initialization proce dure of The Pennsylvania State University-National Center for Atmosphe ric Research Mesoscale Model do not include several of the mesoscale-s ized features observed at 1200 UTC 11 May 1982. 9 h before the develop ment of the first MCS. This is attributed to the lack of observed data with mesoscale resolution, and, therefore, likely is a deficiency in most initialization procedures in use today. Although it is true that new operational observing systems, such as the WSR-88D radar and the 4 04-MHz radar wind profilers, provide more detailed information, the da ta density on the mesoscale remains subcritical. A methodology to incl ude mesoscale features, based upon using subjective interpretations of all the available observations, is developed. It is found that the me soscale initial condition created using this subjective approach produ ces a more reasonable representation of the observed mesoscale feature s in comparison with the conventionally produced initial condition.