The Climate of the
South Platte Basin
Colorado Climate Center
http://climate.atmos.colostate.edu
Key Features of the Climate of
the South Platte Basin
Temperature




Cold winters
Hot summers
Large daily changes
Temperature
decrease with altitude,
especially in summer
Mild zone near
eastern base of
Rockies
Daily Temperatures - Denver, CO
Water Year 2001
120
Temperature (deg F)

100
80
60
40
20
0
-20
Oct
Nov
Dec
Jan
Feb
High
Mar
Low
Apr
Ave High
May
Jun
Ave Low
Jul
Aug
Sep
Humidity

Low humidity but with occasional
intrusions of more humid air
Precipitation

Precipitation varies greatly with topography
Precipitation

Highly seasonal, but seasonal pattern
varies with topography
• High mountains wet in winter-spring and
•
again in later summer
Foothills and eastern plains very dry in winter,
wet in spring and early summer
Precipitation
Monthly Average Precipitation for Selected Sites
in the South Platte Basin
4.00
Hoosier Pass
Denver Stapleton
Sterling
3.50
Precipitation (inches)
3.00
2.50
2.00
1.50
1.00
0.50
0.00
Oct
Nov
Dec
Jan
Feb
Mar
Apr
Month
May
Jun
Jul
Aug
Sep
Precipitation

A few storms contribute a large fraction
of annual precipitation while many small
events contribute a small fraction
Precipitation

A few storms contribute a large fraction
of annual precipitation while many small
events contribute a small fraction
Other Climate Factors

Occasional severe storms
• Tornadoes
• Hail
• Blizzards
• Dust storms
• Front Range Windstorms
• Cold waves
• Etc.
The Pulse of Colorado’s Climate

Tracking long-term variations
Temperature
Seasonal Trends
Fort Collins Winter Average Temperature
(December - February)
Winter Total
7 year running mean
40.0
35.0
Temperature (Deg. F)
30.0
25.0
20.0
15.0
10.0
5.0
0.0
90
18
00
19
10
19
20
19
30
19
40
19
50
19
Years
60
19
70
19
80
19
90
19
00
20
Temperature
Seasonal Trends
Fort Collins Summer Average Temperature
(June - August)
Summer Total
7 year running mean
74
72
Temperature (Deg. F)
70
68
66
64
62
60
58
56
89
18
99
18
09
19
19
19
29
19
39
19
49
19
Years
59
19
69
19
79
19
89
19
99
19
Temperature
Seasonal Trends
Niwot Ridge D-1 Winter Average Temperature
(December - February)
Winter Total
7 Year Running Mean
20
Temperature (Deg. F)
15
10
5
0
-5
-10
90 94 98 02 06 10 14 18 22 26 30 34 38 42 46 50 54 58 62 66 70 74 78 82 86 90 94 98 02 06 10
18 18 18 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 20 20 20
Years
18
90
18
94
18
98
19
02
19
06
19
10
19
14
19
18
19
22
19
26
19
30
19
34
19
38
19
42
19
46
19
50
19
54
19
58
19
62
19
66
19
70
19
74
19
78
19
82
19
86
19
90
19
94
19
98
20
02
20
06
20
10
Temperature (Deg. F)
Temperature
Seasonal Trends
Niwot Ridge D- 1 Summer Average Temperature
60
( June - August)
Summer Average
7 Year Running Mean
50
40
30
20
10
0
Years
Temperature
Akron 4E Winter Average Temperature
(December - February)
Winter Total
7 year running average
40.0
35.0
25.0
20.0
15.0
10.0
5.0
0.0
19
72
19
73
19
74
19
75
19
76
19
78
19
79
19
80
19
81
19
82
19
83
19
84
19
85
19
86
19
87
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
Temperature (Deg. F)
30.0
Years
Temperature
Akron 4E Summer Average Temperature
(June - August)
Summer Total
7 year running average
73.0
72.0
70.0
69.0
68.0
67.0
66.0
65.0
64.0
Years
20
01
19
99
19
97
19
95
19
93
19
91
19
89
19
87
19
85
19
83
19
81
19
79
19
76
19
74
63.0
19
72
Temperature (Deg. F)
71.0
Temperature

Winter warming, spring warming,
summer nighttime warming, fall little
change. Changes with elevation and
location. Trends not consistent
20
03
20
01
19
99
19
97
19
95
19
93
19
91
19
89
19
87
19
85
19
83
19
81
19
79
19
77
19
75
19
73
19
71
19
69
19
67
19
65
19
63
19
61
19
59
19
57
19
55
19
53
19
51
Frequency of Extremes
Longmont
Number of days of 90 degrees and above
90
80
70
60
50
40
30
20
10
0
18
90
18
94
18
98
19
02
19
06
19
10
19
14
19
18
19
22
19
26
19
30
19
34
19
38
19
42
19
46
19
50
19
54
19
58
19
62
19
66
19
70
19
74
19
78
19
82
19
86
19
90
19
94
19
98
20
02
Number of Days
Frequency of Extremes
Fort Collins Winter Season
(July - June)
Total Number of Days of 0 F and lower
40
35
30
25
20
15
10
5
0
Years
18
89
18
93
18
97
19
01
19
05
19
09
19
13
19
17
19
21
19
25
19
29
19
33
19
37
19
41
19
45
19
49
19
53
19
57
19
61
19
65
19
69
19
73
19
77
19
81
19
85
19
89
19
93
19
97
20
01
20
05
Length by number of days
Growing Season
Fort Collins Growing Season Length
(at 32 Degrees F)
Growing Season Length
Years
7 year running mean
200
180
160
140
120
100
80
60
40
20
0
Precipitation
18
90
18
93
18
96
18
99
19
02
19
05
19
08
19
11
19
14
19
17
19
20
19
23
19
26
19
29
19
32
19
35
19
38
19
41
19
44
19
47
19
50
19
53
19
56
19
59
19
62
19
65
19
68
19
71
19
74
19
77
19
80
19
83
19
86
19
89
19
92
19
95
19
98
20
01
Precipitation (inches)
Precipitation
Water Year Totals for Cheesman
30.00
25.00
20.00
15.00
10.00
5.00
0.00
Year
Growing Season Evaporation
Precipitation
Snow Pack
APRIL 1 SNOWPACK COLORADO STATEWIDE
160
148 146
140
130
127
126
120
114
Percent of Average
109
109
104
100
126
120
119
106
112 114
105
104 104
99
97
95
91 93
87
85 87
80
90
89
84
87
74
65
59
60
53
46
40
20
0
68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02
Year
Snow Pack
April 1 Snow Water Equivalent (SWE)
at Hoosier Pass - Elevation 11,400 feet
SWE (in)
40
30
20
10
0
1936 1942 1948 1954 1960 1966 1972 1978 1984 1990 1996 2002
Year
Snow Pack
April 1 Snow Water Equivalent (SWE)
at Deadman Hill - Elevation 10,220 feet
SWE (in)
40
30
20
10
0
1937 1942 1947 1952 1957 1962 1967 1972 1977 1982 1987 1992 1997 2002
Year
Conclusions




Some evidence of warming over past
century in most seasons, magnitude
small to modest except in cities
Warming most apparent at night and
in/near Front Range Cities
Data not as consistent as we would like
Conclusions uncertain
Conclusions



Precipitation highly variable
Precipitation had been showing signs of
increasing, until recent drought
Not all sites show same trends
Conclusions

Evaporation
• Had shown signs of decreasing, until recent
drought

Cloudiness
• Had shown signs of increasing, until recent
•
drought period
Clearly we have more high cirrus clouds than
50 years ago – likely related to aircraft cirrus
Conclusions

Snow pack
• Also varies among observing sites; no
obvious trends

Indication of early snowmelt?
• Still doing analysis – preliminary analysis
shows no trend