WMOD00561

• Title: Snow Accumulation Algorithm for the WSR-80D Radar: Final Report
• Date: 7/1/1998
• Weather Modification - Doc Type: Report

high ridge; KCLE, next to the Cleveland NWS FO; KFTG, 40 km east of Denver on the plains; KGJX,
30 kIn E of Grand Junction, CO, on the 3 kIn elevation Grand Mesa; and KMPX, at the NWS FO in the
Minneapolis suburb of Chanhassen.

Support was provided for a single winter of special data collection of Sand SD for each of the 5 sites.
That winter was 1995-96 for Albany, Cleveland and Denver and 1996-97 for the Grand Mesa and
Minneapolis. Preliminary results from Albany, Cleveland and Denver were presented in previous reports
(Super and Holroyd, 1996, 1997a). However, previously presented data sets have all been reanalyzed
and new data sets have been included. Somewhat different approaches have been used in this report and
the results herein should be considered to supersede those previously reported.

3.3 Radar Calibrations

Radar engineers calibrated KFTG during late January 1996 and found the previous calibration to be
0.3 dB low. This minor adjustment was applied in processing of Ze measured before the OSF calibration
date. Technicians from the Cleveland NWS FO asked for assistance during May 1996, after the winter
of special data collection. The OSF engineers found the radar was seriously out of calibration and fixed
the problem. This raises doubt about whether KCLE was in proper calibration during the 1995-95 winter
or not. One of the OSF engineers involved in the May 1996 calibration examined the "delta system
calibration" record and suggested a correction for each individual storm, in the range +0.6 to + 1.2 dB.
As discussed by Super and Holroyd (1997a), these corrections were applied during KCLE data
processing and analysis. However, analysis of a November 1996 storm, to be discussed, suggests the
corrections may have been in the wrong direction. Consequently, for the reanalysis ofKCLE
measurements done herein, it has been assumed that KCLE was in proper calibration during the 1995-96
winter and that the problem developed after that winter. That is, the suggested dBZ corrections were
removed from the earlier radar data file.

Uncertainty still remains about the results from the Cleveland analysis, especially since the Ze-S relation
developed there has the largest coefficient of the 5 radars. That relation mayor may not be appropriate
for the lake effect storms that affect the "snow belt" region east-northeast of Cleveland where special
gages were operated. It would be desirable to test the Cleveland relation with more recent observations.
This has been possible to do with a single 48 hour period during a major lake effect storm which took
place during November 1996,6 months after the OSF calibration. The special storm study is described
in section 6.8.

Because of its remote location, KGJX is equipped with two separate transmitters and receivers sharing
the same waveguide and antenna. This allows for continued operation if one radar malfunctions during
weather conditions unsuitable for travel to the site. One of the transmitter/receiver pairs was used during
the first portion ofthe 1996-97 winter and the other was used thereafter. Calculation of Ze-S relations for
each transmitter/receiver yielded essentially identical results so all data for the winter have been
combined. The most probable conclusion from this finding is that both radars were properly calibrated.
To the authors' knowledge, there is no reason to suspect that the locally calibrated KENX and KMPX
units were not in proper calibration.

3.4 Additional Regions

Additional data sets will be processed for the Sierra Nevada and Cascade mountain ranges of the western
U.S. and from Alaska. As described later in section 9, the data sets obtained so far from those regions

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