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<br />Surruner showers and thunderstorms, with lTIo'isture pulled in from the Gulf <br />of Nexico and/or the Pacific Coast, occur most commonly from June through <br />September, although thunderstorms can occur as early as late March and as <br />latE~ as October. The local geography and cl irnate is sufficient to provide <br />the atmospheric disturbances and uplift necessary to produce thunderstonns. <br />The corrunon thunderstorms produce less than an 'inch of rainfall, with most <br />yielding less than a half inch. The potentiail exists, hOWeVel" , for. develop- <br />ment of a thundercell which could deposit signHicantly more rainfllll in a <br />shol'1: time. <br />During the early fall (September and early October), there are occasional <br />genet'al rainstorms and thunderstorms caused by dying major Pacific stonns. <br />TheSE! warm air masses, heavily laden with moisture, move in from thE! San <br />Die~o or Baja California area, passing through California, across Ar'izona <br />and 'into Southwestern Colorado. The orographic: lift of the San Jua,n Mountains <br />resul t in general precipitation throughout thE! area, and often thunderstorms <br />in the regions such as the Uncompahgre Va'lley ~Ihere autumn temperat.ures <br />remain high. Here too, the orographic banier's limit the availab'le, moisture <br />within the study area. <br />B. Records <br />There are two sources of precip'itation data for the Montrose area: <br />that maintained by the Uncompahgre Water Users Association (UWUA) and that <br />of the National Weather Service (NWS). <br />The UWUA has kept records for 54 yeal"S, a nd as such is an excell ent and <br />reliable source of 24 hour rainfall data. Additionally, supplemental data <br />is available from which certain intensity relat'ionships may be obtained. <br /> <br />. <br /> <br />5 <br />