WMOD00306 ‎(2)‎

• Title: Discusison of "Weather Modification in Arizona in 1971" by Herbert A. Osborn
• Date: 6/1/1972
• State: AZ
• Weather Modification - Doc Type: Report

On the basis of these observations. there were 23 days when the positive
rainfall anomalies were downwind from the seeding (to south and west)
and only 3 days when downwind was in the direction of negative anomalies
(north and east). Of the latter 3 days (July 19 and 20 and August 7).
none appears to fall in the top quintile of the daily rainfall distribu-
tion. and it may therefore be assumed they contributed little to the
pattern of anomalies. Thus the facts exactly contradict Osborn's thesis.

Osborn questions the possibility of making a more rigorous analysis
than his map of anomalies. McDonald (1969) noted that the anomaly method
gave way about 1952-53 for purposes of weather modification evaluation
to the much more powerful method of target/control regression, with this
and other methods undergoing progressive refinement since that time. A
number of evaluation procedures based on precipitation measurements at
the ground not involving randomization. and therefore applicable to
ARIDROP, have been put forward (e.g.. Howell, 1951; Nason and Lopez.
1967; Stidd, 1967; Elliott. 1969). There are numerous examples in the
open scientific literature of elegant and highly informative applica-
tions of such methods to rainfall data poorer than that available in
Arizona.

The Santa Catalina Experiments

Osborn's second grounds are inferences from experiments reportedly

indicating "apparent loss" of rain associated with seeding, chief 8JIOJlg

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