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6 2.1.4 Convergence PMP for Adjoining Regions The Southwest States Region is bounded on the west by the Pacific Ocean drainage of California. Convergence PMP estimates for that drainage (HMR No. 36) were based on multiplying greatest observed ratios of p/M by ~ (observed precipitation, P, divided by storm moisture, M , multipl~ed by maxi- mum moisture, ~). The P/Ms ratios were associated withSrains at least-oro- graphic locations such as on the floor of the Central Valley of California. Enveloping values of P/M and a regional pattern of M were used to determine a basic convergence PMP ~ndex map for 10 mi2 (26 km2)xfor 6 hours duration. For the Columbia River drainage to the north (HMR No. 43), similar proce- dures for estimating convergence PMP were used. The major difference from HMR No. 36 was that regional patterns of convergence PMP were determined for each month, October through June. These monthly maps incorporated the sea- sonal variations of maximum observed I-day precipitation at groups of least- orographic stations as well as the seasonal variation of maximum moisture. In developing convergence PMP for the present study, reasonable consistency was maintained with values for the two adjoining regions. Also of some interest are PMP estimates for the United States east of the 105th meridian (Schreiner and Riedel 197B, and Riedel et al. 1956). For these studies, the effects of steepening slopes near the 105th meridian in Colorado and New Mexico were not taken into account. Thus, the PMP estimates to the east of the steep slopes of the Rocky Mountains should be considered nonorographic. The steep slopes east of the Continental Divide separate by distances up to 300 miles (483 km), the region of those studies from that of the present study. Sharp gradients in precipitation potential are expected in this intervening region that do not allow detailed comparisons of PMP be- tween the two studies. Some overall general consistency checks can be made, such as the effect of moisture sources on PMP patterns, etc. Checks of this nature have been considered in this study. 2.1.5 Summary of Procedure The approach for convergence PMP in this study follows after but is not identical with that for HMR Nos. 36 and 43. Instead of developing P/Ms ratio envelopes, the greatest moisture-maximized observed rainfalls for least-oro- graphic locations were enveloped. This is equivalent to the previous studies [ (P IMs) envelope x Mx = (P x M,./Ms) envelope]. Monthly patterns of highest moisture and seasonal trends in maximum observed .precipitation were used as guides in interpolating between locations of highest moisture-maximized rain- falls. The resulting patterns are consistent with patterns of convergence PMP in HMR No. 43 and No. 36. The 1000-mb (lOO-kPa) convergence PMP esti- mates were then reduced for effective elevation and barrier. Depth-duration (from 6 to 72 hours) and depth-area ~rom 10 to 5,000 mi2, 26 to 12,950 km2) relations were based on maximum observed precipitation in least-orographic areas of the Southwestern States and those from eastern states data respec- tively. These procedures are in general agreement with those used in HMR No. 36 and HMR No. 43.