WMOD00463

• Title: Final Report on an Investigation of Precipitating Ice Crystals from Natural and Seeded Winter Orographic Clouds
• Date: 6/1/1976
• Weather Modification - Doc Type: Report

seeding material to reach the cloud over Wolf Creek Pass was about one

hour, depending on the wind. Measurements of ice nuclei from airborne

and ground ice n~cleus concentrations with time after generators are

turned on shows nearly a six-hour period is required before concentrations

reach a quasi-steady-state. After generators are turned off, a period of

about 24 hours i~ required before ice nucleus concentrations return to

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the normal backg~ound counts. These estimates are complicated by the

presence of trapping inversions, convection, and variable winds.

Due to wide flucrluations in crystal characteristics during individual

storms and since only portions of many of the storms were seeded, it was

decided to subdivide the storms into three-hour blocks for statistical

investigation. Each three-hour block was identified with. a Durango or

Pagosa Springs sounding. The number of soundings taken during periods

of ice crystal collection determined the number of blocks. Sixty-six

blocks were obtained from the 22 storms, of which 39 were seeded and 27

nonseeded, based upon a criteria to be discussed in the analysis section.

During 1972-73 clogging of the belt channel with snow occurred occasionally.

It was quite obv~ous from the patchiness of ice crystals on the belt when

clogging had occurred. Normally, there was an abrupt end to the presence

of ice crystals on the belt when it became clogged. A few chunks of snow

and crystal fragments would sometimes appear on the belt later. No data
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were analyzed when clogging was evident. A simple modification to the

photographic replica tor allowing for more room above the belt on entering

the camera solved this problem for the following winters.

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