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972 JOURNAL OF APPLIED METEOROLOGY VOLUME 20 HIGH PLAINS COOPERATIVE PROGRAM (HIPLEX) RAWINSONDE SITES r-h- \ ~ ~ ~"-" I L__ .r---'- ." \ GJ' IllLS. PLoo WILES CITY SA --- BILO ~_._--- .._-1..\ SPKo ~._- ~IC \ -GOODLAND --~,--- -r---\ \ L J 'OS i ----- 0 '~G SPRINGS LJ---~ wAf ~. FIG. 1. Map of HIPLEX field sites and special rawinsonde sites and networks used in this study. and concurrent satellite observations of mesoscale cloud structure. The summary is based on cloud characteristics and thermodynamic conditions diag- nosed by a simple one-dimensional, steady-state Lagrangian parcel model, the Great Plains Cloud Model (GPCM), developed by Hirsch (1971). In addition, important thermodynamic features re- lated to cloud-base height, required surface heating, , and stability and moisture profiles are analyzed for all soundings. The results are qualified by taking into account 1) the limitations of one-dimensional, steady-state cloud models and 2) problems related to the natural variability of thermodynamics af- fecting cloud growth. 2. Data a. Rawinsonde observations Rawinsondes were launched regularly at a number of locations throughout the High Plains of the United States as part of the HIPLEX during the summer months from 1975 to 1977 (Fig. 1). The number distribution of soundings by location and year is shown in Table 1. All soundings were checked for hydrostatic consistency and accuracy and only those that passed the checks and which reached beyond the 20 kPa level were accepted for model analysis.! Soundings were made routinely on all days during the field season except when the operation stood down for rest periods and major equipment repairs. These standdown periods were scheduled during periods of no convective activity (generally 10% of each field season). On intensive case study days, soundings were launched every 3 11; however, on most days soundings were launched in the morn- ing between 1200 and 1500 GMT and in -the early afternoon between 1800 and 2000 GMT at sites shown in Fig. 1. In 1975, special mesonet observations from three sites located on a triangular grid of nearly 85 km separation north and east of Miles City, Montana, were analyzed. Days when the three soundings were launched simultaneously were used in this study to examine the spatial variability of thermo- dynamic controls of convection. Limited data sets were obtained from August and September at Good- land on 47 days in 1975. Data from June to September were collected at Big Spring on 57 days when convective activity was expected. In 1976, HIPLEX rawinsondes were also collected at Baker, Montana, located about 75 km east of Miles City, to determine significant variations east of Miles City. Soundings were collected in Montana from May to August. At Goodland, Kansas, and Big Spring and Midland, Texas, observations were taken from May to September. During 1977, special HIPLEX soundings were also observed at Billings, Montana, -225 km west- southwest of Miles City to study conditions in the vicinity of mountain-generated convective clouds and storms. Soundings were collected from May to August in Montana. Special mesoscale rawinsondes were collected for the Goodland HIPLEX site to study the generation and propagation of convective systems from the central Colorado Rockies to western Kansas. These soundings were collected at Limon and South Park, Colorado, from July to mid- August, 1977.2 Goodland and Big Spring soundings were collected from May to September. The GPCM model was initialized using soundings from these data sets on days when satellite observa- tions of cloud types were available in 1976 and 1977. Care was taken that only one sounding per day I .1 1 Matthews, D., and F. Politte, 1981: HIPLEX rawinsonde skew T-Iog P analyses, 1977. Tech. Rep., Water and ,Power Resources Service, Denver, CO 80225, 220 pp. 2 Danielson, K. S., W. R. Cotton and L. Grant, 1978: The transition and propagation of mesoscale convective systems on the High Plains. Final Report to U.S. Bureau of Reclamation by Colorado State University under Contract 7.07-83- V0005.