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<br /> <br />-28- <br /> <br />simultaneous. The original-observat~on form (WE Form 612-14, formerly <br />1009) has a space for indicating the beginning and ending of precipitation. <br />Many observers keep meticulous records in this regard; this information, <br />Which is not published, can be of considerable assistance in special <br />studies. If such information is desired, a copy of the records can be <br />obtained from the respective State Climatologists. <br /> <br />Also, an erroneous date of observation may have been entered in the <br />record. Errors and inconsistencies ?uch as those here described can, in <br />many instances, be disclosed by constructing isochronal maps. <br /> <br />Consistency; of records <br /> <br />No record of precipitation should be assumed to be consistent <br />throughout, unless it is known to be: devoid of changes in exposure, <br />observer, location, and equipment. Available information on such changes <br />is contained in the substation histories published by the Weather Bureau <br />("Key to Meteorological Records Documentation No. 1.1"). These histories <br />were compiled from information available at the time of publication <br />(early fifties); they were not the product of a concerted program to <br />accumulate such information over the; entire period of recordo Some <br />apparent inconsistencies in the Observed records might be explained if <br />the historic information were complete. <br /> <br />Especially in the mountainous West, even a small move in gage <br />location may cause a substantial change in the relative catch of precipi- <br />tation. However, some records have been published under one name for <br />a long period of time, even though the station may have been moved about <br />within the vicinity, either, short or long distances. Changes in exposure <br />such as the construction, of buildings, and the cutting or growth of trees <br />and plants, may cause a change in the precipitation catch. Installation <br />of a windshield often will increase the catch. This increased catch may <br />be more nearly equal to the actual precipitation at the gage site, but <br />will not be consistent with the catch prior to use of the windshield. <br /> <br />In testing a precipitation record for consistency, the first step <br />should be a review of the station-history information. Next, the record <br />should be compared with those from nearby stations considered to be in <br />the same environment, either by double-mass plotting or by the ratio <br />method. The latter method compares ,the records for various periods of <br />time to determine whether the ratio 'is consistent. When the source of <br />moisture changes substantially from :winter to summer as in the Southwest, <br />it is desirable to test consistency for each season separately. Double- <br />mass analysis has been used in most areas of the Southwest to test the <br />consistency of winter records (October-April); the ratio method to test <br />Summer records (May-September totals). <br /> <br />If inconsistencies are apparent" appropriate adjustments sometimes <br />9lre warranted. However, caution should be used in such adjustment and <br />the safest approach, is to adjust only if presumptive causes coincide <br />With dates of inconsistencies. <br />