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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 2017-05-24.

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
64%
15410
28%
45923
23%
15371
69%
15371
40%
25143

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%
541
25%
1532
19%
540
65%
540
40%
865
June1st to 15thNight
69%
495
33%
1320
26%
495
72%
495
55%
672
June16th to endNight
78%
495
26%
1320
22%
495
79%
495
55%
686
July1st to 15thNight
70%
465
14%
1352
12%
465
71%
465
27%
871
July16th to endNight
74%
522
15%
1467
15%
489
75%
489
24%
995
August1st to 15thNight
76%
494
21%
1476
20%
491
76%
491
29%
924
August16th to endNight
76%
525
21%
1745
23%
525
77%
525
32%
1011
September1st to 15thNight
70%
495
23%
1650
25%
495
72%
495
27%
996
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%
46336
Night
5%423423446%57%
46119
TransparencyDay
26%5%11%21%23%11%
46031
Night
27%410%21%24%12%
45925
SeeingDay
8%10%25%33%18%3
5074
Night
8%317%41%26%3
15419

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
421332445%8%59%
2421
June1st to 15thDay
3212323446%65%
2310
16th to endDay
1232445%6%69%
2310
July1st to 15thDay
3215%446%6%8%11%44%
2184
16th to endDay
5%3245%5%8%8%8%11%36%
2285
August1st to 15thDay
5%425%5%46%6%7%9%42%
2145
16th to endDay
5%324435%7%7%10%45%
2103
September1st to 15thDay
8%3145%25%6%7%7%47%
1980
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%41332445%6%56%
1532
June1st to 15thNight
231233245%68%
1320
16th to endNight
112325%5%6%9%61%
1320
July1st to 15thNight
3435%6%5%6%7%7%9%40%
1442
16th to endNight
4325%7%5%8%8%9%9%33%
1575
August1st to 15thNight
3425%7%35%6%7%7%46%
1485
16th to endNight
3325%5%35%7%8%10%44%
1745
September1st to 15thNight
6%326%6%45%6%6%8%42%
1650
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%14%
2424
June1st to 15thDay
18%45%13%26%31%
2310
16th to endDay
14%46%12%25%37%
2310
July1st to 15thDay
28%9%15%14%13%17%
2045
16th to endDay
31%12%18%20%11%5%
2130
August1st to 15thDay
33%9%15%14%15%12%
2130
16th to endDay
29%8%14%19%17%10%
2103
September1st to 15thDay
31%7%12%15%19%13%
1980
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
27%5%9%16%25%15%
1533
June1st to 15thNight
19%36%11%21%37%
1320
16th to endNight
18%5%8%11%20%36%
1320
July1st to 15thNight
37%9%12%11%9%19%
1352
16th to endNight
39%11%15%16%9%7%
1467
August1st to 15thNight
33%10%13%12%14%15%
1476
16th to endNight
30%8%16%18%15%10%
1745
September1st to 15thNight
36%7%11%14%12%17%
1650
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%33%28%14%4
387
June1st to 15thDay
46%23%39%23%2
420
16th to endDay
1117%39%34%5%
420
July1st to 15thDay
4317%46%23%3
284
16th to endDay
6%15%47%24%5%
271
August1st to 15thDay
8%117%43%24%4
255
16th to endDay
8%218%44%22%3
268
September1st to 15thDay
6%430%41%13%2
255
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%5%19%39%23%1
542
June1st to 15thNight
4319%45%26%
495
16th to endNight
2113%43%37%1
495
July1st to 15thNight
410%37%44%3
465
16th to endNight
5%5%32%49%6%
522
August1st to 15thNight
4430%51%8%
494
16th to endNight
6%6%32%47%7%
525
September1st to 15thNight
8%19%42%36%2
495
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 2017-05-25 11:27:38. Version ac04

Copyright 2017 A. Danko


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