An Investigation of Clouds and Precipitation for the Texas High Plains Page: 22
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22
Altocumulus (A ) is one of.the two dominant cloud types in the area.
It is present at each station in sizable amounts throughout the year. The
maximum is associated with the intense convective activity of summer and
is usually due to the merging of slightly developed cumulus clouds at middle
levels. Altocumulus clouds are not usually associated with significant
amounts of precipitation.
Altocumulus castellatus (Acc) is observed frequently in the spring
and summer but is practically non-existent during the remainder of the year.
Cirrus (Ci) is the other dominant cloud type in the area, occurring
in significant amounts during each month of the year. The maximum occurrence
during summer is related to the anvils of cumulonimbus clouds. The space
distribution of cumulonimbus is such that its occurrence may not be reported
at a station even though the cirrus from distant cumulonimbus may be.
Cirrostratus (Cs) and Cirrocumulus (Cc) have been combined due to
their low frequency of occurrence in the area. The combination is dominated
by cirrostratus, cirrocumulus having the lowest frequency of occurrence among
those clouds considered in this investigation. Since cirrostratus is associated
with the frontal activity of winter, the combination shows a mid-winter maximum
and a pronounced minimum during late summer and early fall. The cirrocumulus
which is reported is associated with summer convective activity.
The diurnal variation of seven of the most common cloud types is
shown in Figures 9a, 9b, 9c, and 9d. Mean monthly frequency of occurrence is
plotted against the time of day for each month of the year. Thus, the maxi-
mum frequency at any particular three-hour interval is 30. Midland is not
included in the figures due to its shorter period of record for cloud-type
observations. The statistics for Amarillo and Lubbock are based once again
on 10 years of data.
Cirrus is the dominant cloud type during Januy, occurring nearly
15 times per month during the daylight hours and falling off to a minimum
frequency of about 5 or 6 times per month in the early pre-dawn hours. This
nighttime decrease is probably exaggerated somewhat due to observational
difficulties during darkness. The second most prevalent cloud type is alto-
cumulus. It also has a daytime maximum with peaks at 9 a.m. and 6 p.m. LST.
Weak convective activity is probably producing some late afternoon cumulus.
Stratus, which occurs only 2 or 3 times per month appears to be slightly more
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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/m1/34/: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting UNT Libraries Government Documents Department.