This page made possible by the sponsorship of: Steven D. Schlagel.

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 2005-11-05 to 2018-02-22.

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
65%
16429
29%
48961
24%
16390
70%
16390
41%
26661

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 15thNight
64%
777
30%
2522
28%
776
70%
776
43%
1267
January16th to endNight
64%
832
32%
2704
31%
832
70%
832
42%
1368
February1st to 15thNight
60%
760
27%
2483
25%
759
67%
759
40%
1287
February16th to endNight
55%
660
34%
1991
25%
660
66%
660
39%
1105
March1st to 15thNight
61%
720
33%
1980
23%
720
68%
720
45%
1089
March16th to endNight
57%
768
28%
2112
19%
768
63%
768
42%
1191
April1st to 15thNight
50%
542
24%
1801
18%
542
59%
542
33%
980
April16th to endNight
53%
540
31%
1800
24%
540
66%
540
39%
900
May1st to 15thNight
59%
539
25%
1667
21%
539
64%
539
39%
897
May16th to endNight
60%
562
27%
1588
20%
561
66%
561
40%
893
June1st to 15thNight
69%
540
31%
1440
25%
540
72%
540
56%
725
June16th to endNight
79%
540
29%
1440
25%
540
81%
540
57%
732
July1st to 15thNight
71%
510
13%
1483
12%
510
72%
510
27%
954
July16th to endNight
74%
564
15%
1593
15%
531
74%
531
23%
1092
August1st to 15thNight
75%
539
19%
1611
19%
536
75%
536
29%
1013
August16th to endNight
75%
573
22%
1905
24%
573
76%
573
32%
1105
September1st to 15thNight
71%
540
23%
1800
24%
540
73%
540
29%
1067
September16th to endNight
74%
668
36%
1983
31%
668
77%
668
49%
1012
October1st to 15thNight
69%
720
32%
2160
26%
720
73%
720
48%
1092
October16th to endNight
74%
768
40%
2304
30%
768
80%
768
55%
1090
November1st to 15thNight
73%
787
36%
2307
29%
787
77%
787
54%
1122
November16th to endNight
66%
975
37%
2655
27%
975
71%
975
52%
1370
December1st to 15thNight
60%
975
26%
2730
20%
975
65%
975
43%
1510
December16th to endNight
56%
1030
23%
2902
19%
1030
59%
1030
34%
1800

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
5%42342445%7%56%
49275
Night
5%413323446%58%
49157
TransparencyDay
26%5%10%21%23%11%
48970
Night
26%410%22%24%12%
48963
SeeingDay
7%10%25%33%19%3
6052
Night
8%316%41%26%3
16438

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 15thDay
6%6%14323345%58%
1746
16th to endDay
6%6%23313235%61%
1872
February1st to 15thDay
37%25%422445%57%
1710
16th to endDay
6%7%34435%45%5%49%
1626
March1st to 15thDay
46%23422348%57%
1980
16th to endDay
44343235%46%55%
2112
April1st to 15thDay
5%4245%34447%52%
2146
16th to endDay
44133245%5%6%57%
2160
May1st to 15thDay
4423425%46%7%53%
2280
16th to endDay
421232445%8%59%
2522
June1st to 15thDay
3212323446%66%
2520
16th to endDay
1131345%6%70%
2520
July1st to 15thDay
32145%47%6%8%11%44%
2382
16th to endDay
5%325%6%5%8%7%8%11%36%
2467
August1st to 15thDay
5%425%6%36%6%8%8%42%
2340
16th to endDay
5%324436%7%7%10%45%
2295
September1st to 15thDay
7%3145%35%6%7%7%46%
2160
16th to endDay
6%212313325%65%
1974
October1st to 15thDay
6%23313346%62%
1800
16th to endDay
421332222470%
1920
November1st to 15thDay
4311313236%67%
1867
16th to endDay
5%4121233469%
1632
December1st to 15thDay
7%6%22313347%57%
1560
16th to endDay
7%10%34324446%48%
1684
January1st to 15thNight
5%5%23222235%64%
2522
16th to endNight
7%5%1331223464%
2704
February1st to 15thNight
5%7%14312246%60%
2472
16th to endNight
5%7%14423335%58%
1991
March1st to 15thNight
4423423246%60%
1980
16th to endNight
5%5%24323446%58%
2112
April1st to 15thNight
6%4235%23447%53%
1801
16th to endNight
6%413313345%62%
1800
May1st to 15thNight
5%424423446%57%
1667
16th to endNight
7%41332345%6%57%
1588
June1st to 15thNight
231333246%69%
1440
16th to endNight
11222446%8%63%
1440
July1st to 15thNight
3425%6%5%6%7%7%9%40%
1573
16th to endNight
4326%8%5%8%8%9%9%33%
1701
August1st to 15thNight
4425%6%35%6%7%8%45%
1620
16th to endNight
3325%5%36%7%7%10%44%
1905
September1st to 15thNight
6%326%6%45%6%6%9%43%
1800
16th to endNight
6%31331324465%
1983
October1st to 15thNight
7%21321234465%
2160
16th to endNight
421321233470%
2304
November1st to 15thNight
431221235%5%67%
2307
16th to endNight
6%41221223468%
2655
December1st to 15thNight
7%5%13313335%60%
2730
16th to endNight
7%9%24424335%51%
2902

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 15thDay
28%414%35%16%2
1747
16th to endDay
26%411%32%21%3
1872
February1st to 15thDay
28%5%16%28%15%4
1710
16th to endDay
35%5%8%20%28%2
1626
March1st to 15thDay
26%49%27%28%4
1980
16th to endDay
28%48%23%28%7%
2112
April1st to 15thDay
29%47%21%25%10%
2146
16th to endDay
24%5%8%22%26%12%
2160
May1st to 15thDay
27%6%9%19%28%9%
2280
16th to endDay
22%5%10%15%31%15%
2525
June1st to 15thDay
17%45%14%26%31%
2520
16th to endDay
13%36%11%25%39%
2520
July1st to 15thDay
29%9%14%14%14%17%
2243
16th to endDay
32%12%18%19%10%5%
2312
August1st to 15thDay
33%8%15%15%15%11%
2325
16th to endDay
29%8%13%19%18%9%
2295
September1st to 15thDay
31%7%12%16%20%12%
2160
16th to endDay
21%47%14%32%18%
1974
October1st to 15thDay
22%48%21%29%13%
1800
16th to endDay
19%37%22%35%12%
1920
November1st to 15thDay
18%39%28%32%8%
1867
16th to endDay
19%27%33%28%7%
1632
December1st to 15thDay
28%416%30%14%5%
1560
16th to endDay
36%7%16%24%13%1
1684
January1st to 15thNight
24%312%33%23%2
2522
16th to endNight
25%210%33%23%3
2704
February1st to 15thNight
27%314%30%17%6%
2483
16th to endNight
29%37%20%32%6%
1991
March1st to 15thNight
25%36%28%28%7%
1980
16th to endNight
26%47%20%29%11%
2112
April1st to 15thNight
30%48%18%24%13%
1801
16th to endNight
25%3420%29%16%
1800
May1st to 15thNight
27%49%18%29%10%
1668
16th to endNight
26%5%9%16%24%16%
1589
June1st to 15thNight
18%26%11%22%37%
1440
16th to endNight
16%47%10%20%39%
1440
July1st to 15thNight
36%9%13%11%9%19%
1483
16th to endNight
40%11%14%17%8%6%
1593
August1st to 15thNight
33%10%13%12%14%14%
1611
16th to endNight
30%8%16%18%16%10%
1905
September1st to 15thNight
34%7%12%17%12%15%
1800
16th to endNight
22%36%14%28%23%
1983
October1st to 15thNight
21%46%18%28%20%
2160
16th to endNight
17%26%17%38%16%
2304
November1st to 15thNight
18%37%25%34%10%
2307
16th to endNight
21%16%27%33%8%
2655
December1st to 15thNight
26%314%29%20%4
2730
16th to endNight
36%415%25%16%1
2902

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 15thDay
23%5%20%28%20%1
135
16th to endDay
8%9%20%34%23%4
144
February1st to 15thDay
8%8%25%36%19%
135
16th to endDay
10%19%32%22%14%
112
March1st to 15thDay
10%20%32%20%15%1
270
16th to endDay
7%28%31%21%9%1
288
April1st to 15thDay
12%22%33%19%8%2
269
16th to endDay
12%30%32%20%3
270
May1st to 15thDay
7%21%39%22%9%
288
16th to endDay
7%11%32%28%16%4
423
June1st to 15thDay
47%22%38%24%2
495
16th to endDay
1118%40%31%5%
495
July1st to 15thDay
4317%44%24%5%
347
16th to endDay
7%14%41%27%8%
327
August1st to 15thDay
7%17%43%25%4
315
16th to endDay
8%219%40%24%4
332
September1st to 15thDay
5%327%40%17%4
315
16th to endDay
9%429%38%12%5%
264
October1st to 15thDay
7%8%22%30%22%8%
135
16th to endDay
8%6%20%29%27%7%
144
November1st to 15thDay
8%9%18%31%29%2
135
16th to endDay
11%9%26%34%17%1
135
December1st to 15thDay
8%6%22%46%13%2
135
16th to endDay
13%9%22%35%15%2
144
January1st to 15thNight
9%217%44%22%3
780
16th to endNight
10%317%41%23%4
832
February1st to 15thNight
10%120%48%15%1
764
16th to endNight
10%5%25%47%11%
660
March1st to 15thNight
6%322%43%21%1
720
16th to endNight
7%6%23%39%21%
768
April1st to 15thNight
8%8%27%41%14%
542
16th to endNight
8%8%25%40%16%
540
May1st to 15thNight
7%422%45%18%1
540
16th to endNight
9%420%39%24%1
563
June1st to 15thNight
4319%45%27%1
540
16th to endNight
1112%44%37%1
540
July1st to 15thNight
39%36%44%4
510
16th to endNight
5%5%31%49%6%
564
August1st to 15thNight
5%431%50%8%
539
16th to endNight
6%6%30%48%7%
573
September1st to 15thNight
7%8%40%38%3
540
16th to endNight
8%111%38%34%5%
668
October1st to 15thNight
8%115%45%25%4
720
16th to endNight
5%212%41%30%6%
768
November1st to 15thNight
5%214%44%28%4
787
16th to endNight
8%417%39%24%5%
975
December1st to 15thNight
10%419%45%18%1
975
16th to endNight
13%418%42%18%2
1030
Page generated at 2018-02-23 09:21:36. Version ac04

Copyright 2018 A. Danko


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