WMOD00285 ‎(2)‎

• Title: Feasibility Study of Wintertime Cloud Seeding to Augment Arizona Water Supplies
• Date: 1/1/1987
• State: AZ
• Weather Modification - Doc Type: Report

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information useful for description of conditions where clouds developed
and the precipitation process took place. Such knowledge is useful in
estimating cloud seeding potential. Rawinsonde data enable the study of
the temperature, moisture and wind structurE! over a vertical distance
exceeding 12 km (39,000 ft) within which most important weather occurs.

Historical rawinsonde data were available for Winslow and Tucson in
Arizona. The analyses which follow in this and the following section on
precipitation event studies employ primarily the data collected at
Winslow. Data analyses were performed on the Tucson information as well
but results are employed as a supplement on"ly due to suspected lesser
representativeness at northern locations.

Analyses based on Winslow rawinsonde data must be carefully interpreted
since nearly always the weather balloon relE~ases take place downwind of
the Mogollon Rim (easterly winds change this). Cloud seeding potential
can best be estimated with data collected on the upwind side and over
the barrier of interest. The air layers of interest will generally be
descending over Winslow. Since air warms and dries as it descends, fine-
feature analyses, the results of which are to be extrapolated to the
upwind slope where the air is cooling as it rises and moisture conden-
sation is taking place, must be cautiously l~mployed. This is par-
ticularly true with instability estimates. It is felt such analyses
should be performed on rawinsonde data colll~cted upwind of the barrier.

Additi onally, resul ts from analyses based on wi nd estimates near the
700 mb (about 3 km or 10,000 ft) level obtained from the 1200 Z
(Greenwich Mean Time) rawinsonde ascent must be cautiously employed
since at that time there is a rather deep temperature inversion in the
valley where Winslow is located (Winslow is on the valley floor at
1420 m). A number of wind measurements at this level indicate effects
of the inversion thus yielding, at times, questionable estimates of the
wind and temperature upwind of the barrier. After some examination of
the twice daily rawinsonde data for the period 1976 through the spring
of 1986, it was decided to select for study the months November through
April, since this period appears likely to encompass most cases with
augmentation potential.

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