WMOD00284

• Applicant: Thompson, J.R., G.W. Wilderson, and D.A. Griffith, North American Weather Consultants
• Sponsor Name: USBR
• Title: Cloud Seeding Data Collection, and Analysis Assoc. with the Colo River Augmentation Demonstration Program
• Prepared For: USBR, Divison of Atmospheric Research
• Prepared By: Thompson, Wilderson, Griffith
• Date: 12/1/1987
• State: AZ
• Weather Modification - Doc Type: Scientific Study

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tat ion statistics. The comparisons of the precipitation chara-
cteristics are remarkably similar, suggesting that there may
not be a very significant difference in the precipitation
patterns within winter storms in the two areas. Figure 3.1
reveals that over half of the hours had amounts less than
0.03 inch, which produced less than 20 percent of the storm
total. The exact same result was found in the Grand Mesa
study. Moreover, half the precipitation total was produced
with hourly rates of about 0.09 inches or more, but these
rates only occurred 20 percent of the time. Super et ale
(1986) reported the comparable hourly rate that produced half
the precipitation total was 0.06 inches or more, which also
occurred 20 percent of the time. In Arizona, 20 percent of
the precipitation resulted from the 5 percent of the hours
with intensities greater than 0.17 inch, whereas in Colorado,
20 percent of the precipitation also resulted from 5 percent
of the hours but the hourly rates were considerably less;
that is, greater than 0.11 inch. This difference in rate
during the more intense precipitation periods could be attributed
to the fact that more organized convection appears to occur
in Arizona winter storms than in Colorado, or it could simply
mean that stronger storms, with or without convection, were
sampled in the Arizona data-set. Higher precipitation rates
do not necessarily imply convection. In fact, in Colorado
the highest rates were more often observed to be from stratiform
cloudiness. A similar analysis has not been done for the
Arizona storms but clearly the weather episodes (discussed
in Section 3.1), which produced the most precipitation, and
possibly with the highest hourly intensities, were those classified
as synoptic stratiform (SS).

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