|
EXHIBIT K Climate Information
<br />Source: USDA Soil Conservation Service, Soil Survey of Logan County, Colorado Issued July 1977
<br />SOIL SURVEY
<br />The South Platte River flows diagonally through the
<br />county in a southwest to northeast direction. It drains the
<br />area to the north and west through many intermittent
<br />tributaries; the most important are Pawnee Creek, Lewis
<br />Creek and Cedar Creek. Areas south and east of the
<br />South Platte River drain mainly to the east into the
<br />upper Frenchman tributary of the North Republican
<br />River. In the northwest and northeast parts of the coun-
<br />ty, natural drainageways are well defined, particularly by
<br />the creeks that are entrenched into the underlying shale
<br />formations and gravelly alluvium. The sandhill area paral-
<br />leling the South Platte River on the south side has poorly
<br />defined drainageways.
<br />The valley of the South Platte River varies in width
<br />from 1 mile to 4 miles. Adjacent to the river are the
<br />nearly level bottomlands and low terraces with fluctuat-
<br />ing water tables at depths of 20 to 60 inches. The well
<br />drained higher terraces, mainly on the north side of the
<br />river, are some of the best irrigated soils in the area.
<br />The larger tributaries, Pawnee, Lewis and Cedar
<br />Creeks, have narrow valleys of loamy alluvial deposits
<br />and enter the river from the north. Pawnee creek joins
<br />the river near the town of Atwood, Cedar Creek between
<br />Sterling and Iliff, and Lewis Creek between Iliff and
<br />Proctor.
<br />The area along the north side of the valley floor from
<br />Sterling to the eastern county line is a nearly level to
<br />strongly sloping, high lying old terrace deposit of
<br />stratified alluvium mantled with loamy eolian materials.
<br />This area is divided by many small drainageways that
<br />flow toward the river in a southeasterly direction.
<br />In the northern part of the county, the "Peetz Table,"
<br />as it is known locally, represents a separate physiographic
<br />area in the form of a high, gently rolling plateau which
<br />slopes eastward. In the southeastern part of the county,
<br />the large "Kelley-Leroy Table" is a similar area with
<br />respect to geology and topography. These plateaus are
<br />underlain by calcareous sandstone and stratified sandy
<br />and gravelly old alluvium. Both areas are mantled by a
<br />thin loess deposit that has been reworked by water.
<br />Bordering the Peetz Table on the southwest are the
<br />steep to nearly vertical "Chimney and Lewis Canyons,"
<br />consisting of siltstone exposures capped by calcareous
<br />sandstone of the Ogallala Formation. Southeast of the
<br />"Peetz Table" is a strongly sloping and steep area of red-
<br />dish colored gravelly alluvium occurring as ridges and
<br />resembling remnants of old high terraces. This is dis-
<br />sected by many intermittent drainageways flowing to the
<br />southeast.
<br />In the northwest part of the county, mainly south of
<br />the Chimney and Lewis Canyon area, is a nearly level to
<br />moderately sloping , area with deposits of materials
<br />derived from siltsU a and interbedded sandstone and
<br />shale. Outcrops of shale and siltstone are common in this
<br />area, especially on ridges bordering intermittent
<br />drainageways.
<br />North and west of Sterling is a nearly level to
<br />moderately sloping area that is mantled by a thin veneer
<br />of loess and eolian calcareous sandy materials.
<br />Paralleling the south side of the South Platte River is
<br />an extensive, thick eolian sand deposit with dunelike
<br />topography. This deposit grades into the tableland area in
<br />the southeast part of the county.
<br />Climate
<br />The climate of Logan County is semiarid continental.
<br />Because the county is separated from major sources of
<br />moisture by large distances and mountain ranges, its cli-
<br />mate is characterized by low humidity, wide variations in
<br />precipitation and temperature, and abundant sunshine.
<br />Logan County is usually warm in summer with
<br />frequent hot days. The highest temperature occurs during
<br />July and August. In winter, periods of very cold weather
<br />are caused by Arctic air moving in from the north or
<br />northeast. Cold periods alternate with milder periods that
<br />occur often when westerly winds are warmed as they
<br />move downslope. Most precipitation falls as rain during
<br />the warmer part of the year and is normally heaviest in
<br />late spring and early summer. Winter snowfalls are
<br />frequent, but snow cover usually disappears during mild
<br />periods.
<br />The mean annual precipitation in Logan County ranges
<br />from 13 inches in the western part to nearly 19 inches in
<br />the eastern part. Most of the precipitation occurs during
<br />the growing season, commonly as thunderstorms. Not all
<br />of this precipitation is effective for plant growth because
<br />of high runoff.
<br />Table 1 gives data on temperature and precipitation for
<br />Logan County, as recorded at Sterling for the period 1951
<br />to 1973. Table 2 shows probable dates of the first freeze
<br />in fall and the last freeze in spring. Table 3 provides data
<br />on length of the growing season.
<br />In winter the average temperature is 27.5 degrees F,
<br />and the average daily minimum is 13.7 degrees. The
<br />lowest temperature on record, -29 degrees, occurred at
<br />Sterling on February 1, 1951. In summer the average
<br />temperature is 71 degrees, and the average daily max-
<br />imum is 86.3 degrees.
<br />Growing degree days, shown in table 3, are equivalent
<br />to "heat units." During the month, growing degree days
<br />accumulate by the amount that the average temperature
<br />each day exceeds a base temperature. The normal
<br />monthly accumulation is used to schedule single or succes-
<br />sive plantings of a crop between the last freeze in spring
<br />and the first freeze in fall.
<br />Of the total annual precipitation, 12.27 inches, or 81
<br />percent, usually falls in April through September, which
<br />includes the growing season for most crops. In 2 years
<br />out of 10, the April-September rainfall is less than 10
<br />inches. The heaviest 1-day rainfall during the period of
<br />record was 4.88 inches on August 15, 1968. Thun-
<br />derstorms occur on about 45 days each year, and most
<br />occur in June and July.
<br />Average seasonal snowfall is 29.9 inches. The greatest
<br />snow depth at any one time during the period of record
<br />was 20 inches. On the average, 12 days have at least 1
|