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 2017-09-10.

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%
15731
28%
46871
23%
15692
70%
15692
40%
25685

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%
717
29%
2327
28%
716
70%
716
43%
1177
January16th to endNight
62%
768
31%
2496
30%
768
68%
768
40%
1285
February1st to 15thNight
60%
700
26%
2288
25%
699
67%
699
40%
1190
February16th to endNight
55%
632
33%
1905
24%
632
66%
632
39%
1058
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%
525
22%
1750
24%
525
73%
525
28%
1048
September16th to endNight
75%
612
35%
1818
30%
612
78%
612
51%
913
October1st to 15thNight
69%
660
33%
1980
26%
660
73%
660
46%
1024
October16th to endNight
73%
704
38%
2112
29%
704
80%
704
54%
1008
November1st to 15thNight
73%
725
37%
2125
30%
725
77%
725
53%
1034
November16th to endNight
65%
900
35%
2451
25%
900
70%
900
52%
1272
December1st to 15thNight
59%
900
25%
2520
19%
900
63%
900
42%
1411
December16th to endNight
55%
951
22%
2679
17%
951
58%
951
32%
1694

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%55%
47741
Night
5%423423446%57%
47067
TransparencyDay
26%5%11%21%23%11%
47436
Night
27%410%21%23%12%
46873
SeeingDay
8%10%24%33%19%3
5542
Night
8%317%41%26%3
15740

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
7%6%14213335%58%
1611
16th to endDay
7%7%23313235%59%
1728
February1st to 15thDay
37%24422445%57%
1575
16th to endDay
6%7%24435%45%5%49%
1566
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
8%4145%35%6%7%7%46%
2097
16th to endDay
5%212313335%66%
1809
October1st to 15thDay
7%34313346%61%
1650
16th to endDay
421322223469%
1760
November1st to 15thDay
4311313236%67%
1720
16th to endDay
5%4121233468%
1507
December1st to 15thDay
7%6%32313336%56%
1440
16th to endDay
8%10%34324346%47%
1554
January1st to 15thNight
5%6%2422313464%
2327
16th to endNight
7%5%1341223462%
2496
February1st to 15thNight
5%7%24312336%59%
2277
16th to endNight
5%7%1442332459%
1905
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%8%42%
1750
16th to endNight
5%31331333466%
1818
October1st to 15thNight
8%31321234463%
1980
16th to endNight
421321233470%
2112
November1st to 15thNight
431221235%467%
2125
16th to endNight
6%42221223468%
2451
December1st to 15thNight
7%6%13313335%59%
2520
16th to endNight
8%9%34424435%49%
2679

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
27%414%35%15%1
1612
16th to endDay
28%412%30%20%3
1728
February1st to 15thDay
28%5%17%27%16%4
1575
16th to endDay
34%5%8%20%28%2
1566
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%15%19%12%
2097
16th to endDay
20%48%15%32%18%
1809
October1st to 15thDay
23%47%22%30%11%
1650
16th to endDay
20%27%22%36%11%
1760
November1st to 15thDay
18%39%27%32%8%
1720
16th to endDay
19%28%33%28%7%
1507
December1st to 15thDay
30%417%31%13%2
1440
16th to endDay
38%7%16%24%12%1
1554
January1st to 15thNight
25%312%33%23%2
2327
16th to endNight
27%310%31%23%3
2496
February1st to 15thNight
27%314%29%17%7%
2288
16th to endNight
29%37%19%33%6%
1905
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
35%7%12%16%12%16%
1750
16th to endNight
20%37%14%29%24%
1818
October1st to 15thNight
23%47%18%28%19%
1980
16th to endNight
18%26%18%38%16%
2112
November1st to 15thNight
18%37%25%34%11%
2125
16th to endNight
22%17%26%33%9%
2451
December1st to 15thNight
27%315%30%20%2
2520
16th to endNight
37%415%25%15%1
2679

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
34%5%17%25%16%
90
16th to endDay
11%10%20%33%18%5%
96
February1st to 15thDay
8%5%21%40%23%1
90
16th to endDay
9%20%30%22%16%1
93
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%427%41%16%4
294
16th to endDay
8%425%40%13%6%
208
October1st to 15thDay
6%5%17%34%24%11%
90
16th to endDay
10%5%20%31%25%7%
96
November1st to 15thDay
10%10%11%31%34%3
90
16th to endDay
15%13%26%28%15%
90
December1st to 15thDay
11%7%24%50%6%
90
16th to endDay
19%11%20%32%15%
96
January1st to 15thNight
9%217%43%22%4
720
16th to endNight
11%317%41%22%4
768
February1st to 15thNight
10%120%48%16%2
704
16th to endNight
9%5%25%46%11%
632
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%41%38%3
525
16th to endNight
7%110%37%36%6%
612
October1st to 15thNight
9%114%43%26%4
660
16th to endNight
6%213%42%29%6%
704
November1st to 15thNight
5%314%42%29%4
725
16th to endNight
8%5%18%38%23%5%
900
December1st to 15thNight
11%420%45%17%1
900
16th to endNight
14%419%41%18%2
951
Page generated at 2017-09-11 17:35:30. Version ac04

Copyright 2017 A. Danko


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