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<br />. <br /> <br />.~ <br /> <br />. <br /> <br />0748 <br /> <br />. <br /> <br />19.. Major Storms. - The principal requisite for the occurrenQ€ of <br /> <br /> <br />major storms is the presence of mari ti,ue tropical air from the Gulf of <br /> <br /> <br />1~xioo. This air, when subjected to violent lifting, is productive of <br /> <br /> <br />heavy precipitation. The mechanism effectin~ the vertical displacement <br /> <br /> <br />of the moist air may be convection, orographic lifting, frontal lifting, <br /> <br /> <br />or a combination thereof. During a major storm period, precipitation <br /> <br /> <br />may result from two or more of these different feature~; the most in- <br /> <br /> <br />tense precipitation is usually caused by a single phase of lifting, that <br /> <br /> <br />which characterizes the type of storm. Often a general storm is accom- <br /> <br /> <br />panied or preceded by thunderstorms of either orographic or convective <br /> <br /> <br />cause. This condition was true in the case of the storm of September 29- <br /> <br /> <br />30, 1904. The major portion of the precipitation was produced by the <br /> <br /> <br />formation of a staole wave on a cold front which had become stationary <br /> <br /> <br />across northern New l1exico and southeastern Colorado. Convective and <br /> <br /> <br />orographic instability showers occurred from the 26th to 29th but the <br /> <br /> <br />intensities were not sufficient to produce a large runoff even from <br /> <br /> <br />small areas. With the passage of the front, the combined effect of the <br /> <br /> <br />orographic barrier along the southern drainage divide plus the frontal <br /> <br /> <br />lifting of the cold wedge caused precipitation of such intensities as <br /> <br /> <br />to result in the maximum peak discharge of the Purgatoire River at <br /> <br /> <br />Trinidad. <br /> <br /> <br />20. The storm of July 22, 1925, is a good example of the high <br /> <br /> <br />intensity precipitation that occurs as the result of convective in- <br /> <br /> <br />stgbility. The storm was local in nature reaching cloudburst proportions <br /> <br /> <br />in the area from Weston to Segundo. These local convective type storms <br /> <br /> <br />may be aided in lifting by orographic effects. Other examples of this <br /> <br /> <br />type of storm are the storms of August 7, 1929, and September 15, 1934. <br /> <br /> <br />21. Antecedent conditions to the storm of April 23, 1942, con- <br /> <br /> <br />sisted of an anticyclone over the southeastern states carrying maritime <br /> <br /> <br />tropical air into southeastern Colorado and resulting in orographic <br /> <br />2l <br /> <br />APPENDIX B <br /> <br />. .'~ '" . <br /> <br />"';,. <br /> <br />,_,;b_~ ~ -;, " <br /> <br />