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<br />001400 <br /> <br />Unnoted change in location of station.- As will be treated at <br />greater length, a change in location of a station may divide a <br />precipitation record into parts that are not consistent one with <br />another. If the changed location is overlooked or is not of record~ <br />a substantial error may result. <br /> <br />Recording gages at remote stations.- At high, remote sites where <br />precipitst~on MAY fall as either rain or snow, and where several months <br />may elapse,between servicing trips, presently available recording gages <br />commonly fail to operate continuously. Consequently there are serious <br />gaps in knowledge of short-term precipitation rates at such sites, with <br />resultant possible errors in interpretation. <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 Sub-Station Histories (Key to Meteorological Records <br />Documentation No. 1.1) recently published by the Weather Bureau. These <br />histories were compiled from information available at the time of publica.tion <br />(early :fifties); they were not the product of a concerted program to <br />accumulate'such information over the entire period of record. Some apparent <br />inconsistencies in the observed records might be explained if the historic <br />information were complete. <br /> <br />Especially in the mountainous West, even a small move in gage location <br />may cause ~ substantial change in the relative catch of precipitation. <br />However, some records have been published under one name for a long period <br />of time, even though the station may have been moved about within the <br />vicinity, either short or long distances. Changes in exposure, such as the <br />cutting of trees, construction of buildings, or the gradual growth of trees <br />and plants may cause a change in the precipitation catch. Installation of <br />a windshield often will increase the catch. This increased catch may be <br />more nearJi equal to the actual precipitation at the gage site, but will <br />not be consistent with the catch prior t.o 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 ~ompared with those from nearby stations, either by double-mass <br />plotting or by the ratio method. The latter method compares' the records <br />for variou$ perio<t of time to determine whether the ratio has changed. <br />When the source of moisture changes substantially from season to season <br />as in the Southwest, it is desirable to test consistency for each season <br />separately. The double-mass technique has been used in most areas of the <br />Southwest to test the consistency of winter records (October-April); the <br />ratio method. to test summer records (May-September totals). <br /> <br /> <br />11.4 <br />