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<br />November 1, 1973, to September 30, 1980, have been archived on magnetic <br />tape. Data for 53 grid blocks, covering Oklahoma and the Texas panhandle for <br />April 1 to September 30 for the years 1974 to 1980, were used in this study. <br />The data were derived from radars located in Amarillo and Stephenville, <br />Texas; Garden City and Wichita, Kansas; Little Rock, Arkansas; Monett, <br />Missouri; and Oklahoma City, Oklahoma. The MDR code number represents the <br />rainfall intensity and the areal coverage of echoes for each block. These <br />code numbers range from 0, indicating no echoes observed in the block, to 9, <br />indicating heavy to intense rainfall over more than half the block. In 1978, <br />a new MDR reporting grid was implemented, which has grid blocks about 40 km <br />on a side. The highest intensity code of the four new blocks, which corres- <br />pond most nearly with one old block, was recorded, and an analysis of code <br />frequencies indicated that the new data are compatible with the old data. <br />The Oklahoma Climatological Survey prepared "calendars" (26 weeks by 24 <br />hours) of echo frequencies and selected echo intensities for each of the <br />53 study blocks as shown in figure 5. Analysis of the frequency calendars <br />indicated that the study area could be divided into six diurnal rainfall <br />regimes. <br /> <br />The panhandles of both Texas and Oklahoma are characterized by a strong <br />diurnal rain cloud frequency pattern throughout the year. The maximum in <br />rain cloud frequency occurs between 1800 and 1900 l.s.t (local standard <br />time); the minimum occurs around 0800 l.s.t. The pattern is most pronounced <br />in late July and early August. <br /> <br />Northwest Oklahoma also has a pronounced diurnal variation in rain cloud <br />frequency, but there the pattern is strongest in the spring .and autumn, with <br />the lowest rain cloud frequencies found in June and July. The autumn maximum <br />occurs approximately 2 hours earlier than that of the spring (1630 l.s.t. vs. <br />1830 1. s . t. ) . <br /> <br />In southwest Oklahoma, as in the panhandles, <br />in late summer and is weakest in the spring. <br />maximum in summer occurs around 1500 l.s.t. <br /> <br />the diurnal variation is strongest <br />The rain cloud frequency <br /> <br />22 <br />