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11 The major nonsummer general storms such as February 3-8, 1937, November 25-28, 1905 and December 14-17, 1908, also indicated less than 3 inch (76 mm) total storm amounts for least-orographic stations. Taken collectively, and excluding the Porter storm, the amounts listed in table 2.1 are the greatest known general-storm convergence point rainfalls for the Southwest. The storm values were adjusted to a common elevation and duration, and to optimum moisture conditions. The adjustments are as follows: a. Adjustment for elevation. The events of table 2.1 were adjusted to sea level (assumed 1000 mb, 100 kPa). This adjustment is the ratio of the avail- able precipitable water above 1000 mb (100 kPa) to that available above the surface. Where adjustments were necessary, the precipitable water was de- termined using the storm l2-hr persisting 1000-mb (lOO-kPa) dew point and assuming a pseudo-adiabatic saturated atmosphere ( U. S. Weather Bureau 1951a). b. Adjustment for duration. A generalized durational variation determined for convergence PMP was applied to obtain a common duration of 24 hours for all the storms. Reference is made to figures and tables discussed in section 2.4 for the generalized relation. A monthly 6/24-hr ratio was interpolated from the appropriate map (figs. 2.25 to 2.27) at the location of storm rain- fall. Entering table 2.7 or figure 2.20 with the 6/24-hr ratio and the dura- tion of the rain amount gives the factor by which the rain amount needs to be adjusted to provide an estimated amount for the 24-hr duration. c. Adjustment for maximum moisture. One of the steps in estimating PMP is to adjust observed storms to the maximum moisture potential for the storm location and date. Maximum l2-hr persisting 1000-mb (lOO-kPa) general-storm dew points (Schwarz and Hansen 1978) were used in this adjustment. The ad- justment assumes a pseudo-adiabatic lapse rate with a saturated atmosphere and is the ratio of precipitable water for the maximum 1000-mb (lOO-kPa) dew point to that for the storm. dew point at a location representative of the inflow moisture. A further maximization was made by allowing the maximum l2-hr persisting 1000-mb (lOO-kPa) dew point to be read 15 days toward the seasonal maximum. 2.2.2 Enveloping l2-hr Persisting Dew Points Enveloping l2-hr persisting dew points have been developed and presented in HMR Nos. 36 and 43 and on a national basis in the Climatic Atlas ~nvironment- al Science Services Administration 196B). The companion volume to the present study (Schwarz and Hansen 1978) updates the data for the Southwest and develops both general-and local-storm l2-hr maximum persisting 1000-mb (lOo-kPa) dew points. 2.2.3 Regional Patterns The adjusted storm amounts in the last column of table 2.1 were plotted at their respective locations on a map (not shown). The few data points pro- vided the lowest level of convergence PMP to be considered at 'these locations but were insufficient to define a regional pattern.