Geoscience Reference
In-Depth Information
Fig. 3.7. Average maximum temperatures, 1981-2010. the
highest maximum temperatures correspond approximately
with the longest frost-free periods and the highest rates of
potential evapotranspiration. From Wyoming Water Resources
Data System, prepared with PRiSM climate Group data,
oregon State University (http://www.prism.oregonstate.edu/
terms.phtml). cartography by christopher nicholson.
Temperature, Frost-Free Period, and Evaporation
rapid warming and cooling even in the lowlands, espe-
cially when there are few or no clouds.
Historically, the mean frost-free period varies from
125 days to fewer than 25 days, with the longest peri-
ods occurring in the Bighorn Basin, in a small area near
Riverton in the Wind River Basin, and on the eastern
plains (see fig. 3.7). Such areas have the largest amount
of cropland. crop plants generally do not tolerate frost,
though many native plants do. Significantly, although
temperature has an important effect on the initiation of
plant growth in the spring, the termination of growth
is more often caused by drought, especially in the low-
lands where precipitation is lower. native plants can tol-
erate short growing seasons; most crop plants require
irrigation. Fallow dryland farming is an alternative,
which allows such crops as wheat to benefit from 2 years
of soil moisture accumulation rather than 1 year.
the July mean daily high temperature ranges from 90°F,
such as on the Great Plains and in the Bighorn Basin, to
less than 75°F in the higher mountains. 10 the July mean
annual low temperature is 55°F on the plains and near
freezing in the alpine zone, where frost at night is com-
mon even in the summer (fig. 3.7). During a 24-hour
period, variation is most extreme in the alpine tundra,
where air temperature near the ground may be 80°F or
more during the day and below freezing at night. Such
extreme variation is caused by rapid heating of the soil
during the day (stemming from reduced water vapor in
the atmosphere of the alpine zone), and, for the same
reason, rapid cooling at night. Although most plants
can acclimate to cold temperatures, many cannot adapt
to such extreme diurnal cycles. notably, the whole
region is comparatively high and dry, with relatively
 
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