WMOD00459

• Title: Snow Accumulation Algorithm for the WSR-88D Radar, Version 1
• Date: 6/1/1996
• Weather Modification - Doc Type: Report

Development of the initial prototype Algorithm is the subject of sections 10 to 13,
although calculations of a and P coefficients is discussed in section 9.

4. Collect high-quality observations of Sand SD during the winter/spring of 1995-96 near
Denver, Colorado. In the context of the MOU, snow depth refers to the depth of freshly-
fallen snow in the absence of melting, compaction by surface heating or other factors, or
redistribution by the wind. These S measurements (5 locations) and SD measurements
(1 location) will be used for further Algorithm testing and refinement. This task is
discussed in section 3.3.

5. Obtain good-quality observations of Sand SD in a climatological area with WSR-88D
coverage other than the Denver area during the winter/spring of 1995-96. This
observational program, called. "more limited" (than Denver's program) in the SOW, ended
up in the Albany, New York, area. The Albany WFO (Weather Forecast Office) of the
NWS (National Weather Service) installed and operated a large volunteer observer
network, which is discussed in section 3.2. Availability of the Albany Sand SD
measurements has been delayed by quality ~ontrol checking. Observations of S from the
Cleveland, Ohio, area, scheduled for November 1, 1996, delivery, have been substituted
for Albany observations in this report.

6. Based on the MOU Supplement No.1 of August 1995, install and maintain five Belfort
Universal recording precipitation gages from mid-November 1995 through March 1996
between the near and far ranges of the Cleveland WSR-88D. The gages were deployed
parallel to the south shore of Lake Erie. The main purpose of this line of gages was to
investigate lake effect storms and the ability of the WSR-88D system to detect snow and
estimate snowfall accumulation as a function of range. The Cleveland measurement
program is discussed in section 3.4.

2. Observations from the 1994.95 Winter

As discussed in more detail in the quarterly reports, only a limited number of NEXRAD
systems was equipped with functioning Level II recorders during the 1994-95 winter, and
those systems were typically located in the southern half of the continental U.S. A key
measurement provided on Level II data tapes is Ze for each l-km by r range bin out to a
.230-km range. A range bin is the basic spatial unit for which these data are recorded.
Doppler velocities and spectrum width are also provided, but at 0.25-km by 10 resolution.

Denver was the northernmost radar with Level II data during the winter in question (the
Boise, Idaho, Level II recorder was not functional). Other radars with operational Level II
recorders, located even farther south and at lower elevations than Denver, likely observed
frequent bright band returns associated with melting snowflakes. Dry snowfall cases were
probably infrequent at those locations and no effort was made to obtain data from them.
Instead, it was decided to concentrate on data collection during the 1995-96 winter when
many more WSR-88Ds would be equipped with Level II recorders.

The high-resolution (0.0 I-inch) Belfort Universal gage at the Denver (Stapleton Airport) WFO
was discontinued with the March 1, 1995, opening of DIA (Denver International Airport).
The convention in this nation of using English units for measurement of precipitation and
snow depth is followed throughout this report. The DIA ASOS (automated surface
observation station) non-heated tipping bucket gage does not provide suitable observations

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