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Meso-f3 Scale Analysis I Grid I"" I PO +0 + + 33. Rain gage network I I + BG MA 0+ + + +SE . 31.8N 102. 101' 100.6. 1---94km---j / / / / 102.4.W IAM/ I / ~/PO-' S~ LA 0 SN o I BG0 / MA 0 SE / f,) 0Y -"-..r / GSW ~ r ~I 472 km Synoptic-scale network vcr ~ ~ Synoptic Rowinsonde Site o Meso-f3 Rowinsonde Site + Surfoce Automotic Weother Stations (PROS E) Figure 3.1-Map of the Texas HIPLEX field site showing mesoscale networks. is given in the final report to the Bureau by Texas DWR (Riggio et al.. 1 983); details can be found in the annual reports and in numerous reports by subcon- tractor groups. This section of the present report is intended only to summarize some of the major pro- gram accomplishments. 3.2 Rainfall Characteristics West Texas is noted for the extreme variability of its weather. Although two-thirds of Big Spring's mean annual rainfall of 442 mm (17.4 in) comes during the half year. April through September. droughts are not uncommon during this same period. When the rain- fall does come. during the spring and summer months. it is usually from several relatively large storm systems that migrate across the region. drenching some localities and missing adjacent ones. Substantial rainfalls in September usually re- flect the movement of tropical depressions into the region from the Gulf of Mexico. The early years of Texas HIPLEX stressed rainfall characteristics as estimated by radar and rain gages. Rain gage data were recorded on Belfort weighing instruments. digitized at 1 5-minute intervals. and stored in the Bureau's EON (Environmental Data Network). The density of recording gages increased from one gage per 104 km2 initially to one gage per 25 km2 during the 1979 and 1980 field seasons. 32. The west Texas rainstorms were found to be highly variable. Rain volumes ranged from as much as 5.1 x 109 m3 (419 000 acre-h) to as little as 1.1 x 105 m3 (87 acre-ft) per storm. Rainfall events were classified using radar and rain gage data by scientists at Texas Tech University. Four categories of convective storms were established based upon the scale of organization: (1) convective cells. (2) small convective clusters. (3) large convective clusters. and (4) nested convective clusters. includ- ing lines. Figure 3.2 shows an example of the rain gage analysis of a typical cluster event which pro- duced 57 x 106 m3 of rainfall. These studies. sum- marized in table 3.2. found. as expected. that a few rainstorms were responsible for a large percentage of the area's total rainfall. 3.3 Cloud Sizes Studies were carried out to show more exactly how the well-known correlation between cloud size and rainfall production per storm applies in west Texas. Estimates of cloud size were based on satellite pho- tographs and on recorded radar echoes. It was recognized that radar echoes correspond to precip- itation volumes within the clouds rather than to the entire cloud-filled volume. Satellite cloud photographs were obtained from the National Weather Service in Lubbock. Texas. in 1979 and 1980. These real-time visible and infrared satellite images were obtained at the project opera- tions office in Big Spring every 30 minutes during the field season. Figure 3.3 shows typical convective clouds viewed from the satellite on May 28. 1979. Digital satellite imagery was collected at CSU (Colo- rado State University) (Reynolds et al.. 1979) during the periods of interest and analyzed by Jurica and Chi (1979) and Jurica etal. (1981) using the CSU digital imagery processing system. Sutherland et al. (1980). estimated the radar echo top temperatures as measured by the M-33 radar and rawinsondes. Tops colder than -5 0 C. which is often considered a condition necessary for ice-phase seeding. were rare in isolated cells but were the rule in organized clusters. The more organized systems were deeper and lasted longer than the isolated cells. Jurica et al. (1981) found that practically all radar echoes from showers reached to more than 8.7 km (28000 ft) above sea level. Matthews (1983) found that 46 percent of the echoes observed in 1979 12