Colorado Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colorado Skies Observatory clear sky chart from 2005-11-06 to 2024-03-08.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
61%
24473
27%
80020
22%
24384
67%
24384
38%
42920

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
57%
748
26%
4031
24%
736
66%
736
23%
2164
January11th to 20thNight
56%
757
29%
4031
28%
740
65%
740
26%
1933
January21st to endNight
56%
825
21%
4348
27%
814
64%
814
22%
2330
February1st to 10thNight
53%
760
29%
2470
24%
760
63%
760
41%
1266
February11th to 20thNight
52%
741
28%
2350
21%
740
62%
740
37%
1286
February21st to endNight
46%
628
32%
1860
21%
628
57%
628
39%
1037
March1st to 10thNight
53%
750
30%
2062
20%
750
61%
750
42%
1167
March11th to 20thNight
55%
720
29%
1980
20%
720
61%
720
40%
1155
March21st to endNight
49%
792
27%
2178
14%
792
59%
792
38%
1277
April1st to 10thNight
49%
546
27%
1806
19%
546
60%
546
35%
947
April11th to 20thNight
48%
533
28%
1777
20%
533
61%
533
35%
920
April21st to endNight
52%
540
31%
1800
22%
540
66%
540
40%
894
May1st to 10thNight
57%
540
30%
1693
25%
540
65%
540
42%
860
May11th to 20thNight
59%
531
25%
1594
21%
531
63%
531
36%
903
May21st to endNight
58%
583
28%
1604
20%
582
65%
582
43%
892
June1st to 10thNight
71%
540
32%
1440
25%
540
74%
540
55%
727
June11th to 20thNight
72%
540
33%
1440
26%
540
75%
540
60%
713
June21st to endNight
76%
540
29%
1440
24%
540
79%
540
55%
744
July1st to 10thNight
76%
525
17%
1504
15%
525
76%
525
35%
896
July11th to 20thNight
76%
522
18%
1566
16%
522
77%
522
31%
951
July21st to endNight
73%
591
14%
1674
13%
558
74%
558
24%
1141
August1st to 10thNight
74%
537
19%
1602
17%
534
75%
534
30%
991
August11th to 20thNight
72%
534
23%
1683
24%
534
73%
534
33%
991
August21st to endNight
75%
594
23%
1980
25%
594
77%
594
34%
1096
September1st to 10thNight
72%
540
25%
1800
28%
540
74%
540
32%
1018
September11th to 20thNight
71%
558
33%
1818
33%
558
74%
558
39%
966
September21st to endNight
71%
720
33%
2054
26%
720
75%
720
51%
1056
October1st to 10thNight
63%
720
28%
2160
21%
720
68%
720
40%
1182
October11th to 20thNight
71%
720
38%
2160
28%
720
78%
720
59%
991
October21st to endNight
67%
792
40%
2376
27%
792
76%
792
54%
1133
November1st to 10thNight
73%
740
39%
2220
30%
740
79%
740
57%
1025
November11th to 20thNight
66%
895
39%
2415
26%
895
73%
895
62%
1160
November21st to endNight
60%
950
33%
2645
23%
950
66%
950
46%
1415
December1st to 10thNight
56%
950
28%
2660
20%
950
62%
950
43%
1476
December11th to 20thNight
51%
948
24%
3142
18%
948
57%
948
31%
1861
December21st to endNight
50%
1023
14%
4657
16%
1012
55%
1012
24%
2356

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
45%244345%5%7%57%
78740
Night
5%6%2442445%6%57%
80875
TransparencyDay
25%6%11%21%24%13%
78465
Night
27%6%10%21%24%13%
80671
SeeingDay
7%10%26%33%20%4
14168
Night
8%420%42%23%3
24513

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
37%36%4345%6%7%53%
2858
11th to 20thDay
46%244345%6%7%55%
2860
21st to endDay
6%8%35%425%45%6%52%
3146
February1st to 10thDay
37%25%5%3345%5%57%
1710
11th to 20thDay
5%8%35%5%43446%51%
1717
21st to endDay
5%9%45%5%35%46%6%50%
1591
March1st to 10thDay
6%7%25%5%3346%8%51%
2058
11th to 20thDay
47%35%4345%6%8%51%
1980
21st to endDay
5%6%35%4345%5%7%51%
2178
April1st to 10thDay
44246%445%5%6%57%
2153
11th to 20thDay
34344345%6%8%56%
2131
21st to endDay
4424435%5%5%7%58%
2160
May1st to 10thDay
442443445%7%59%
2263
11th to 20thDay
5%4245%35%6%7%9%52%
2301
21st to endDay
432342445%7%63%
2667
June1st to 10thDay
32233235%5%6%66%
2520
11th to 20thDay
2212223445%74%
2520
21st to endDay
21124345%7%7%65%
2520
July1st to 10thDay
3214446%6%8%10%51%
2405
11th to 20thDay
33145%5%7%7%7%10%48%
2340
21st to endDay
6%425%6%5%8%8%8%11%38%
2545
August1st to 10thDay
5%425%6%46%6%9%10%44%
2328
11th to 20thDay
4425%6%46%7%7%8%49%
2216
21st to endDay
5%324435%6%7%9%51%
2376
September1st to 10thDay
7%4135%35%6%6%8%52%
2160
11th to 20thDay
5%223435%5%5%6%59%
2138
21st to endDay
6%312323346%68%
1904
October1st to 10thDay
8%41443445%7%58%
1800
11th to 20thDay
421322223475%
1800
21st to endDay
4314323235%70%
1980
November1st to 10thDay
4311313337%70%
1859
11th to 20thDay
3322313446%70%
1744
21st to endDay
6%6%1332333464%
1531
December1st to 10thDay
7%7%33323247%59%
1520
11th to 20thDay
7%7%245%345%6%8%49%
1926
21st to endDay
6%8%35%3245%46%54%
2835
January1st to 10thNight
37%49%7%44446%50%
4097
11th to 20thNight
49%34323346%59%
4110
21st to endNight
6%8%36%5%23346%53%
4521
February1st to 10thNight
5%8%24422346%61%
2470
11th to 20thNight
7%7%24423346%57%
2349
21st to endNight
6%9%25%423335%58%
1860
March1st to 10thNight
5%5%345%3435%7%56%
2062
11th to 20thNight
5%7%25%42445%6%55%
1980
21st to endNight
6%7%24434446%55%
2178
April1st to 10thNight
6%5%245%3445%7%56%
1806
11th to 20thNight
7%5%25%4235%5%6%57%
1777
21st to endNight
6%5%133245%5%6%60%
1800
May1st to 10thNight
6%424323446%60%
1693
11th to 20thNight
7%5%25%42446%6%54%
1594
21st to endNight
6%5%2342445%6%59%
1604
June1st to 10thNight
2324323347%68%
1440
11th to 20thNight
3313323346%70%
1440
21st to endNight
2212425%5%6%9%61%
1440
July1st to 10thNight
34245%5%6%6%7%10%47%
1549
11th to 20thNight
4425%6%47%7%8%10%45%
1620
21st to endNight
5%437%8%5%8%9%10%10%33%
1773
August1st to 10thNight
3326%8%45%7%7%9%46%
1611
11th to 20thNight
5%5%35%6%35%6%6%9%47%
1683
21st to endNight
4425%5%35%6%8%10%48%
1980
September1st to 10thNight
5%326%5%45%6%7%9%46%
1800
11th to 20thNight
6%425%5%35%446%57%
1818
21st to endNight
7%313322345%67%
2054
October1st to 10thNight
10%424323445%59%
2160
11th to 20thNight
4313212335%74%
2160
21st to endNight
431332234470%
2376
November1st to 10thNight
5%31221345%5%71%
2220
11th to 20thNight
2322212345%74%
2415
21st to endNight
8%5%23322245%63%
2645
December1st to 10thNight
7%6%24423345%61%
2660
11th to 20thNight
8%7%25%4345%5%6%52%
3271
21st to endNight
8%9%35%423335%55%
4859

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
27%8%17%27%17%3
2859
11th to 20thDay
26%7%18%32%14%3
2860
21st to endDay
29%8%13%30%18%2
3146
February1st to 10thDay
28%6%14%25%20%7%
1710
11th to 20thDay
33%5%10%25%23%3
1726
21st to endDay
33%6%8%17%29%7%
1591
March1st to 10thDay
29%6%8%23%26%7%
2058
11th to 20thDay
28%6%11%24%25%7%
1980
21st to endDay
30%5%9%23%26%6%
2178
April1st to 10thDay
26%5%8%20%27%14%
2153
11th to 20thDay
24%6%9%20%25%16%
2134
21st to endDay
24%6%8%22%29%12%
2160
May1st to 10thDay
23%5%9%19%32%13%
2263
11th to 20thDay
26%8%11%18%25%11%
2304
21st to endDay
20%5%10%14%30%22%
2667
June1st to 10thDay
17%5%8%17%28%26%
2520
11th to 20thDay
12%45%12%24%42%
2520
21st to endDay
16%5%8%14%23%34%
2520
July1st to 10thDay
23%9%14%15%15%24%
2341
11th to 20thDay
24%10%16%19%17%14%
2271
21st to endDay
32%13%20%19%11%4
2404
August1st to 10thDay
30%10%17%13%14%16%
2313
11th to 20thDay
28%8%13%16%18%16%
2216
21st to endDay
25%8%13%19%22%12%
2376
September1st to 10thDay
27%7%11%14%22%19%
2160
11th to 20thDay
22%7%11%15%24%20%
2138
21st to endDay
19%47%16%34%19%
1904
October1st to 10thDay
25%7%11%17%23%18%
1800
11th to 20thDay
15%2418%38%22%
1800
21st to endDay
19%49%23%35%11%
1980
November1st to 10thDay
16%39%27%36%10%
1859
11th to 20thDay
16%48%30%36%6%
1744
21st to endDay
25%37%27%28%9%
1531
December1st to 10thDay
27%5%15%28%18%7%
1520
11th to 20thDay
33%7%12%28%18%2
1924
21st to endDay
29%7%13%18%27%7%
2835
January1st to 10thNight
32%8%11%27%20%2
4097
11th to 20thNight
28%6%15%30%18%3
4110
21st to endNight
32%7%11%30%16%3
4521
February1st to 10thNight
26%412%28%21%9%
2470
11th to 20thNight
29%49%24%26%7%
2350
21st to endNight
30%38%18%30%11%
1860
March1st to 10thNight
27%5%7%24%28%9%
2062
11th to 20thNight
28%6%7%23%24%12%
1980
21st to endNight
29%5%9%21%28%8%
2178
April1st to 10thNight
28%47%18%28%15%
1806
11th to 20thNight
27%47%17%26%19%
1777
21st to endNight
24%47%19%31%15%
1800
May1st to 10thNight
24%48%17%33%14%
1693
11th to 20thNight
28%7%9%19%23%13%
1595
21st to endNight
25%5%9%16%23%22%
1604
June1st to 10thNight
18%48%15%24%31%
1440
11th to 20thNight
16%37%10%18%46%
1440
21st to endNight
17%6%9%14%20%34%
1440
July1st to 10thNight
29%9%14%13%10%25%
1504
11th to 20thNight
32%9%13%16%12%18%
1566
21st to endNight
38%14%19%15%9%5%
1674
August1st to 10thNight
31%12%15%13%13%16%
1602
11th to 20thNight
31%8%14%14%14%18%
1683
21st to endNight
28%9%14%19%17%13%
1980
September1st to 10thNight
30%8%13%16%14%19%
1800
11th to 20thNight
27%5%10%15%18%26%
1818
21st to endNight
21%46%13%31%26%
2054
October1st to 10thNight
26%6%8%15%21%24%
2160
11th to 20thNight
15%45%13%36%27%
2160
21st to endNight
18%36%21%35%16%
2376
November1st to 10thNight
16%36%25%37%13%
2220
11th to 20thNight
15%27%29%38%9%
2415
21st to endNight
25%37%23%33%9%
2645
December1st to 10thNight
27%313%28%22%6%
2660
11th to 20thNight
32%7%12%26%20%3
3272
21st to endNight
32%411%19%25%9%
4859

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
11%10%31%31%17%1
270
11th to 20thDay
12%14%31%27%14%1
270
21st to endDay
6%6%28%39%17%4
297
February1st to 10thDay
7%13%36%33%11%1
270
11th to 20thDay
10%12%40%27%10%
270
21st to endDay
12%17%39%25%6%
246
March1st to 10thDay
9%17%39%22%12%
449
11th to 20thDay
9%20%31%26%12%2
420
21st to endDay
12%27%36%17%7%1
462
April1st to 10thDay
11%19%36%23%9%2
420
11th to 20thDay
12%26%29%23%8%1
412
21st to endDay
9%26%34%24%7%1
420
May1st to 10thDay
7%21%39%24%9%
423
11th to 20thDay
8%14%33%27%17%2
448
21st to endDay
6%12%31%31%17%3
622
June1st to 10thDay
36%22%42%24%3
630
11th to 20thDay
27%26%38%22%4
630
21st to endDay
25%22%41%28%3
630
July1st to 10thDay
3314%40%34%6%
511
11th to 20thDay
2113%37%35%12%
444
21st to endDay
6%110%36%37%10%
487
August1st to 10thDay
6%315%38%32%6%
447
11th to 20thDay
3420%39%27%7%
437
21st to endDay
6%215%41%29%7%
495
September1st to 10thDay
6%417%36%28%8%
450
11th to 20thDay
4422%44%22%5%
450
21st to endDay
7%6%26%30%22%7%
374
October1st to 10thDay
8%9%23%24%27%9%
270
11th to 20thDay
6%12%17%37%21%6%
270
21st to endDay
9%8%24%33%23%3
297
November1st to 10thDay
8%11%26%32%21%2
270
11th to 20thDay
5%6%30%38%18%3
270
21st to endDay
10%9%26%32%18%5%
270
December1st to 10thDay
10%12%24%37%11%6%
270
11th to 20thDay
8%11%26%35%16%3
270
21st to endDay
15%11%31%31%10%1
297
January1st to 10thNight
9%324%43%18%3
760
11th to 20thNight
8%324%42%20%2
760
21st to endNight
9%424%41%19%3
836
February1st to 10thNight
10%5%28%44%13%1
760
11th to 20thNight
10%429%45%12%1
744
21st to endNight
12%5%32%43%7%
628
March1st to 10thNight
7%5%30%43%13%2
750
11th to 20thNight
8%5%25%40%21%1
720
21st to endNight
8%9%29%39%15%1
792
April1st to 10thNight
8%9%30%43%10%
546
11th to 20thNight
10%10%27%40%14%
533
21st to endNight
7%9%30%41%14%
540
May1st to 10thNight
8%5%26%44%17%1
540
11th to 20thNight
9%421%44%20%2
531
21st to endNight
9%5%24%41%20%1
584
June1st to 10thNight
3417%49%25%1
540
11th to 20thNight
3318%49%25%2
540
21st to endNight
2314%46%34%1
540
July1st to 10thNight
418%43%42%2
525
11th to 20thNight
417%37%45%6%
522
21st to endNight
5%17%35%47%6%
591
August1st to 10thNight
416%34%48%8%
537
11th to 20thNight
6%28%41%38%4
534
21st to endNight
6%17%38%43%5%
594
September1st to 10thNight
6%19%43%37%4
540
11th to 20thNight
7%111%46%33%2
558
21st to endNight
8%313%41%31%4
720
October1st to 10thNight
11%317%42%24%3
720
11th to 20thNight
4217%49%24%3
720
21st to endNight
6%419%43%24%5%
792
November1st to 10thNight
6%316%48%25%4
740
11th to 20thNight
3423%45%20%4
895
21st to endNight
10%6%20%38%22%4
950
December1st to 10thNight
9%5%24%43%16%2
950
11th to 20thNight
12%5%25%38%18%1
950
21st to endNight
12%6%24%43%13%1
1031
Page generated at 2024-03-05 05:24:00. Version ac07

Copyright © 2024 Attilla Danko.


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