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<br />4.5 Advection <br /> <br />It initially seemed advantageous to use a wind advection scheme to select the range bin or bins most <br />likely to have produced the larger snow particles reaching the surface measurement. A wind advection <br />scheme was developed for the SAA as described by Super and Holroyd (1 997a) It used the vertical wind <br />profile calculated by the V AD (Velocity Azimuth Display) technique and assumed constant fall <br />velocities representative of large snow particles. The scheme was abandoned when comparisons revealed <br />that it failed to increase the degree of association (correlation coefficient) with surface observations over <br />simply using the nearest neighbor range bin. <br /> <br />4.6 Winter Observations <br /> <br />4.6.1 Observations/rom the 1994-95 Winter <br /> <br />As discussed in more detail in the early quarterly reports to the OSF and by Super and Holroyd (1996), <br />only a limited number ofNEXRAD systems were equipped with functioning Level II recorders during <br />the 1994-95 winter, and those systems were typically located in the southern half of the continental U.S. <br />Precipitation gage data were also vastly inadequate for proper analysis. Instead, it was decided to <br />concentrate on data collection during the 1995-96 winter when many more WSR-88Ds would be <br />equipped with Level II recorders. <br /> <br />4.6.2 Observations/rom the 1995-96 Winter <br /> <br />Networks of precipitation gages were deployed around Denver, Cleveland, and Albany. Details are given <br />in Super and Holroyd (1996 and 1997a). The Albany network was operated by the NWS there. These <br />data provided the data used for determining the constants in the equation relating reflectivity to snowfall. <br /> <br />4.6.3 Observations/rom the 1996-97 Winter <br /> <br />As reported by Super and Holroyd (1997a), snowfall observations continued during the 1996-97 winter at <br />Albany with hourly reports from about a hundred volunteer observers. Cleveland also had numerous <br />volunteers who made twice daily observations. Only limited use was made of these observations for <br />SAA development. Denver area observations by Reclamation were discontinued because of the need to <br />deploy equipment elsewhere. <br /> <br />Reclamation gages were moved to a line west-northwest of the Minneapolis radar for the winter of <br />1996-97 for comparison with Ze observations from that radar. <br /> <br />Three Reclamation gages were operated relatively close to the Grand Junction radar on top of the Grand <br />Mesa in the preferred small clearings in the widespread conifer forest. The most intense snowfall rates <br />of any location were observed by these gages. Previous experience at this location indicates that the <br />abrupt forced orographic uplift enhances precipitation on the Grand Mesa. <br /> <br />Measurements from gages maintained by other agencies will be used with radar observations in the <br />Sierra Nevada Mountains as observed from Buell AFB in California, the Northern Cascade Mountains as <br />observed from Seattle, and the areas around Anchorage, Alaska. These observations are described in <br />section 9. <br /> <br />10 <br />