An Investigation of Clouds and Precipitation for the Texas High Plains Page: 45
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4.5
effective, since once the necessary vertical motion is provided, the precip-
itation follows almost without exception. The highly localized nature of the
precipitation is associated with the equally localized fields of vertical
motion. The one hope which modification might hold is that these disturbances,
often accompanied by hail and violent winds, could be made less violent by
cloud seeding operations. Hail suppression experiments in the Soviet Union
(Sokol, 1967) utilizing control areas and statistical analysis have suggested
that seeding may reduce hail losses by as much as 90%.
Summer rainfall in the plains area is made up of scattered showery
developments which depend mainly upon daytime heating, low-level moisture,
and the absence of subsidence aloft. During much of the summer, the extension
of the Atlantic anticyclone westward brings upper-level stability and inhibits
vertical development in any but isolated cases. As will be discussed in the
next section, general rainfall covering large areas and whose duration is
greater than a few hours, is associated, even during the summer season, with
frontal activity.
Heavy late summer and early autumn rainfall over most of Texas is
mainly the result of tropical disturbances moving northward and westward from
the Gulf of Mexico. In the plains area, frontal passages are becoming more
frequent, and this, coupled with the Gulf moisture leads to an extension of
the summer rainy season into the early fall. Late autumn and winter rains
are usually the result of warm moist Gulf air overrunning continental polar
air which is associated with a strong winter anticyclone.
The period from early November until mid-April is characteristically
dry in the plains. Precipitation averages over a 50-year period (Portig, 1962)
indicate that more than 80% of the annual rainfall occurs during the seven
month period, April thru October. It is this rainy season which is of primary
concern here.
Rainfall records at Amarillo are complete since 1892 while the period
of record at Lubbock dates from 1911. These data are available in the climatic
summaries of the United States published by the United States Department of
Commerce Weather Bureau (1932, 1955, 1965). Frequency distributions of precip-
itation based on these periods of record are illustrated by percentage ogives
in Figure 16 for Amarillo and Figure 17 for Lubbock. The ordinate in the
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Haragan, Donald R. An Investigation of Clouds and Precipitation for the Texas High Plains, report, March 1970; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth839452/m1/57/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.