WMOD00454

• Title: Preliminary Analysis of the Hypotheses Used in the Utah Operational Weather Modification Program - Final Report
• Date: 11/1/1983
• Weather Modification - Doc Type: Report

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these measurements, vertical time sections of temperature, dewpoint depression,

potential temperature, equivalent potential temperature, and wind speed were

constructed. These are shown in Figures 6, 7, and 8. In conjunction with

Ku-band radar, these analyses were used to determine the mesoscale structure

of the evolving storm system.

3. Frontal Structure

Figure 6 shows the vertical potential temperature and wind speed

time section for storm 9. Surface frontal passage is evident between

l800Z and 2000Z. The precise time of frontal passage at Adamsville

was 1940Z. Winds were southwesterly and relatively weak throughout

the depth of the atmosphere until well after trough passage. After

trough passage winds shifted to northwesterly, gradually increasing in

speed throughout the period. Ridge development to the west of Utah,

combined with the deepening trough to the east, led to the development

of a high-level northwesterly jet in the upper troposphere by the end

of the storm. This had no significant effect on the storm characteristics,

since virtually all precipitation occurred in the pre-trough environment.

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b. Moisture

The rawinsonde time-section analysis of temperature and dewpoint-

depression for 8 February 1983 is displayed in Figure 7. The pre-frontal

environment during this storm was characterized by saturated conditions

extending from the surface to 450 mb. The depth of this moisture

coincided well with observed radar cloud tops during the period. At or

near frontal passage, a rapid transition to a much dryer airmass occurred

at all levels above 600 mb. The lower levels of the atmosphere remained

saturated throughout the episode. Isolines in Figure 7 result from a

linear interpolation between rawinsonde measurements and do not reflect